Mars Archives

August 17, 2016August 21, 2016 by Matt Williams

What are the Planets of the Solar System?

An illustration showing the 8 planets of the Solar System to scale Credit: NASA

At one time, humans believed that the Earth was the center of the Universe; that the Sun, Moon, planets and stars all revolved around us. It was only after centuries of ongoing observations and improved instrumentation that astronomers came to understand that we are in fact part a larger system of planets that revolve around the Sun. And it has only been within the last century that we’ve come to understand just how big our Solar System is.

And even now, we are still learning. In the past few decades, the total number of celestial bodies and moons that are known to orbit the Sun has expanded. We have also come to debate the definition of “planet” (a controversial topic indeed!) and introduced additional classifications – like dwarf planet, minor planet, plutoid, etc. – to account for new finds. So just how many planets are there and what is special about them? Let’s run through them one by one, shall we?

Mercury:

As you travel outward from the Sun, Mercury is the closest planet. It orbits the Sun at an average distance of 58 million km (36 million mi). Mercury is airless, and so without any significant atmosphere to hold in the heat, it has dramatic temperature differences. The side that faces the Sun experiences temperatures as high as 420 °C (788 °F), and then the side in shadow goes down to -173 °C (-279.4 °F).

Like Venus, Earth and Mars, Mercury is a terrestrial planet, which means it is composed largely of refractory minerals such as the silicates and metals such as iron and nickel. These elements are also differentiated between a metallic core and a silicate mantle and crust, with Mercury possessing a larger-than-average core. Multiple theories have been proposed to explain this, the most widely accepted being that the impact from a planetesimal in the past blew off much of its mantle material.

Mercury is the smallest planet in the Solar System, measuring just 4879 km across at its equator. However, it is second densest planet in the Solar System, with a density of 5.427 g/cm³ – which is the second only to Earth. Because of this, Mercury experiences a gravitational pull that is roughly 38% that of Earth’s (0.38 g).

Mercury also has the most eccentric orbit of any planet in the Solar System (0.205), which means its distance from the Sun ranges from 46 to 70 million km (29-43 million mi). The planet also takes 87.969 Earth days to complete an orbit. But with an average orbital speed of 47.362 km/s, Mercury also takes 58.646 days to complete a single rotation.

Combined with its eccentric orbit, this means that it takes 176 Earth days for the Sun to return to the same place in the sky (i.e. a solar day) on Mercury, which is twice as long as a single Hermian year. Mercury also has the lowest axial tilt of any planet in the Solar System – approximately 0.027 degrees – compared to Jupiter’s 3.1 degrees, which is the second smallest.

The MESSENGER spacecraft has been in orbit around Mercury since March 2011 – but its days are numbered. Image credit: NASA/JHUAPL/Carnegie Institution of Washington — *The MESSENGER spacecraft has been in orbit around Mercury since March 2011 – but its days are numbered. Credit: NASA/JHUAPL/Carnegie Institution of Washington*

Mercury has only been visited two times by spacecraft, the first being the Mariner 10 probe, which conducted a flyby of the planet back in the mid-1970s. It wasn’t until 2008 that another spacecraft from Earth made a close flyby of Mercury (the MESSENGER probe) which took new images of its surface, shed light on its geological history, and confirmed the presence of water ice and organic molecules in its northern polar region.

In summary, Mercury is made special by the fact it is small, eccentric, and varies between extremes of hot and cold. It’s also very mineral rich, and quite dense!

Venus:

Venus is the second planet in the Solar System, and is Earth’s virtual twin in terms of size and mass. With a mass of 4.8676×10²⁴ kg and a mean radius of about 6,052 km, it is approximately 81.5% as massive as Earth and 95% as large. Like Earth (and Mercury and Mars), it is a terrestrial planet, composed of rocks and minerals that are differentiated.

But apart from these similarities, Venus is very different from Earth. Its atmosphere is composed primarily of carbon dioxide (96%), along with nitrogen and a few other gases. This dense cloud cloaks the planet, making surface observation very difficult, and helps heat it up to 460 °C (860 °F). The atmospheric pressure is also 92 times that of Earth’s atmosphere, and poisonous clouds of carbon dioxide and sulfuric acid rain are commonplace.

At a closest average distance of 41 million km (25,476,219 mi), Venus is the closest planet to Earth. Credit: NASA/JPL/Magellan — *Venus’ similarity in size and mass has led to it being called “Earth’s sister planet’. Credit: NASA/JPL/Magellan*

Venus orbits the Sun at an average distance of about 0.72 AU (108 million km; 67 million mi) with almost no eccentricity. In fact, with its farthest orbit (aphelion) of 0.728 AU (108,939,000 km) and closest orbit (perihelion) of 0.718 AU (107,477,000 km), it has the most circular orbit of any planet in the Solar System. The planet completes an orbit around the Sun every 224.65 days, meaning that a year on Venus is 61.5% as long as a year on Earth.

When Venus lies between Earth and the Sun, a position known as inferior conjunction, it makes the closest approach to Earth of any planet, at an average distance of 41 million km. This takes place, on average, once every 584 days, and is the reason why Venus is the closest planet to Earth. The planet completes an orbit around the Sun every 224.65 days, meaning that a year on Venus is 61.5% as long as a year on Earth.

Unlike most other planets in the Solar System, which rotate on their axes in an counter-clockwise direction, Venus rotates clockwise (called “retrograde” rotation). It also rotates very slowly, taking 243 Earth days to complete a single rotation. This is not only the slowest rotation period of any planet, it also means that a single day on Venus lasts longer than a Venusian year.

Venus’ atmosphere is also known to experience lightning storms. Since Venus does not experience rainfall (except in the form of sulfuric acid), it has been theorized that the lightning is being caused by volcanic eruptions. Several spacecraft have visited Venus, and a few landers have even made it to the surface to send back images of its hellish landscape. Even though there were made of metal, these landers only survived a few hours at best.

Venus is made special by the fact that it is very much like Earth, but also radically different. It’s thick atmosphere could crush a living being, its heat could melt lead, and its acid rain could dissolve flesh, bone and metal alike! It also rotates very slowly, and backwards relative to the other plants.

Earth:

Earth is our home, and the third planet from the Sun. With a mean radius of 6371 km and a mass of 5.97×10²⁴ kg, it is the fifth largest and fifth most-massive planet in the Solar System. And with a mean density of 5.514 g/cm³, it is the densest planet in the Solar System. Like Mercury, Venus and Mars, Earth is a terrestrial planet.

But unlike these other planets, Earth’s core is differentiated between a solid inner core and liquid outer core. The outer core also spins in the opposite direction as the planet, which is believed to create a dynamo effect that gives Earth its protective magnetosphere. Combined with a atmosphere that is neither too thin nor too thick, Earth is the only planet in the Solar System known to support life.

The Earth's layers, showing the Inner and Outer Core, the Mantle, and Crust. Credit: discovermagazine.com — *The Earth’s layers, showing the Inner and Outer Core, the Mantle, and Crust. Credit: discovermagazine.com*

In terms of its orbit, Earth has a very minor eccentricity (approx. 0.0167) and ranges in its distance from the Sun between 147,095,000 km (0.983 AU) at perihelion to 151,930,000 km (1.015 AU) at aphelion. This works out to an average distance (aka. semi-major axis) of 149,598,261 km, which is the basis of a single Astronomical Unit (AU)

The Earth has an orbital period of 365.25 days, which is the equivalent of 1.000017 Julian years. This means that every four years (in what is known as a Leap Year), the Earth calendar must include an extra day. Though a single solar day on Earth is considered to be 24 hours long, our planet takes precisely 23h 56m and 4 s to complete a single sidereal rotation (0.997 Earth days).

Earth’s axis is also tilted 23.439281° away from the perpendicular of its orbital plane, which is responsible for producing seasonal variations on the planet’s surface with a period of one tropical year (365.24 solar days). In addition to producing variations in terms of temperature, this also results in variations in the amount of sunlight a hemisphere receives during the course of a year.

Earth has only a single moon: the Moon. Thanks to examinations of Moon rocks that were brought back to Earth by the Apollo missions, the predominant theory states that the Moon was created roughly 4.5 billion years ago from a collision between Earth and a Mars-sized object (known as Theia). This collision created a massive cloud of debris that began circling our planet, which eventually coalesced to form the Moon we see today.

*A picture of Earth taken by Apollo 11 astronauts. Credit: NASA*

What makes Earth special, you know, aside from the fact that it is our home and where we originated? It is the only planet in the Solar System where liquid, flowing water exists in abundance on its surface, has a viable atmosphere, and a protective magnetosphere. In other words, it is the only planet (or Solar body) that we know of where life can exist on the surface.

In addition, no planet in the Solar System has been studied as well as Earth, whether it be from the surface or from space. Thousands of spacecraft have been launched to study the planet, measuring its atmosphere, land masses, vegetation, water, and human impact. Our understanding of what makes our planet unique in our Solar System has helped in the search for Earth-like planets in other systems.

Mars:

The fourth planet from the Sun is Mars, which is also the second smallest planet in the Solar System. It has a radius of approximately 3,396 km at its equator, and 3,376 km at its polar regions – which is the equivalent of roughly 0.53 Earths. While it is roughly half the size of Earth, it’s mass – 6.4185 x 10²³ kg – is only 0.151 that of Earth’s. It’s density is also lower than Earths, which leads to it experiencing about 1/3rd Earth’s gravity (0.376 g).

It’s axial tilt is very similar to Earth’s, being inclined 25.19° to its orbital plane (Earth’s axial tilt is just over 23°), which means Mars also experiences seasons. Mars has almost no atmosphere to help trap heat from the Sun, and so temperatures can plunge to a low of -140 °C (-220 °F) in the Martian winter. However, at the height of summer, temperatures can get up to 20 °C (68 °F) during midday at the equator.

However, recent data obtained by the Curiosity rover and numerous orbiters have concluded that Mars once had a denser atmosphere. Its loss, according to data obtained by NASA’s Mars Atmosphere and Volatile Evolution (MAVEN), the atmosphere was stripped away by solar wind over the course of a 500 million year period, beginning 4.2 billion years ago.

At its greatest distance from the Sun (aphelion), Mars orbits at a distance of 1.666 AUs, or 249.2 million km. At perihelion, when it is closest to the Sun, it orbits at a distance of 1.3814 AUs, or 206.7 million km. At this distance, Mars takes 686.971 Earth days, the equivalent of 1.88 Earth years, to complete a rotation of the Sun. In Martian days (aka. Sols, which are equal to one day and 40 Earth minutes), a Martian year is 668.5991 Sols.

Like Mercury, Venus, and Earth, Mars is a terrestrial planet, composed mainly of silicate rock and metals that are differentiated between a core, mantle and crust. The red-orange appearance of the Martian surface is caused by iron oxide, more commonly known as hematite (or rust). The presence of other minerals in the surface dust allow for other common surface colors, including golden, brown, tan, green, and others.

Although liquid water cannot exist on Mars’ surface, owing to its thin atmosphere, large concentrations of ice water exist within the polar ice caps – Planum Boreum and Planum Australe. In addition, a permafrost mantle stretches from the pole to latitudes of about 60°, meaning that water exists beneath much of the Martian surface in the form of ice water. Radar data and soil samples have confirmed the presence of shallow subsurface water at the middle latitudes as well.

*MSL Curiosity selfie on the surface of Mars. Image: NASA/JPL/Cal-Tech*

Mars has two tiny asteroid-sized moons: Phobos and Deimos. Because of their size and shape, the predominant theory is that Mars acquired these two moons after they were kicked out of the Asteroid Belt by Jupiter’s gravity.

Mars has been heavily studied by spacecraft. There are multiple rovers and landers currently on the surface and a small fleet of orbiters flying overhead. Recent missions include the Curiosity Rover, which gathered ample evidence on Mars’ water past, and the groundbreaking discovery of finding organic molecules on the surface. Upcoming missions include NASA’s InSight lander and the Exomars rover.

Hence, Mars’ special nature lies in the fact that it also is terrestrial and lies within the outer edge of the Sun’s habitable zone. And whereas it is a cold, dry place today, it once had an thicker atmosphere and plentiful water on its surface.

Jupiter:

Mighty Jupiter is the fouth planet for our Sun and the biggest planet in our Solar System. Jupiter’s mass, volume, surface area and mean circumference are 1.8981 x 10²⁷ kg, 1.43128 x 10¹⁵ km³, 6.1419 x 10¹⁰ km², and 4.39264 x 10⁵ km respectively. To put that in perspective, Jupiter diameter is roughly 11 times that of Earth, and 2.5 times the mass of all the other planets in the Solar System combined.

But, being a gas giant, it has a relatively low density – 1.326 g/cm³– which is less than one quarter of Earth’s. This means that while Jupiter’s volume is equivalent to about 1,321 Earths, it is only 318 times as massive. The low density is one way scientists are able to determine that it is made mostly of gases, though the debate still rages on what exists at its core (see below).

Jupiter orbits the Sun at an average distance (semi-major axis) of 778,299,000 km (5.2 AU), ranging from 740,550,000 km (4.95 AU) at perihelion and 816,040,000 km (5.455 AU) at aphelion. At this distance, Jupiter takes 11.8618 Earth years to complete a single orbit of the Sun. In other words, a single Jovian year lasts the equivalent of 4,332.59 Earth days.

However, Jupiter’s rotation is the fastest of all the Solar System’s planets, completing a rotation on its axis in slightly less than ten hours (9 hours, 55 minutes and 30 seconds to be exact). Therefore, a single Jovian year lasts 10,475.8 Jovian solar days. This orbital period is two-fifths that of Saturn, which means that the two largest planets in our Solar System form a 5:2 orbital resonance.

Much like Earth, Jupiter experiences auroras near its northern and southern poles. But on Jupiter, the auroral activity is much more intense and rarely ever stops. The intense radiation, Jupiter’s magnetic field, and the abundance of material from Io’s volcanoes that react with Jupiter’s ionosphere create a light show that is truly spectacular.

The Juno spacecraft isn't the first one to visit Jupiter. Galileo went there in the mid 90's, and Voyager 1 snapped a nice picture of the clouds on its mission. Image: NASA — *The Juno spacecraft isn’t the first one to visit Jupiter. Galileo went there in the mid 90’s, and Voyager 1 snapped a nice picture of the clouds on its mission. Credit: NASA*

Jupiter also experiences violent weather patterns. Wind speeds of 100 m/s (360 km/h) are common in zonal jets, and can reach as high as 620 kph (385 mph). Storms form within hours and can become thousands of km in diameter overnight. One storm, the Great Red Spot, has been raging since at least the late 1600s. The storm has been shrinking and expanding throughout its history; but in 2012, it was suggested that the Giant Red Spot might eventually disappear.

Jupiter is composed primarily of gaseous and liquid matter. It is the largest of the gas giants, and like them, is divided between a gaseous outer atmosphere and an interior that is made up of denser materials. It’s upper atmosphere is composed of about 88–92% hydrogen and 8–12% helium by percent volume of gas molecules, and approx. 75% hydrogen and 24% helium by mass, with the remaining one percent consisting of other elements.

The interior contains denser materials, such that the distribution is roughly 71% hydrogen, 24% helium and 5% other elements by mass. It is believed that Jupiter’s core is a dense mix of elements – a surrounding layer of liquid metallic hydrogen with some helium, and an outer layer predominantly of molecular hydrogen. The core has also been described as rocky, but this remains unknown as well.

Jupiter has been visited by several spacecraft, including NASA’s Pioneer 10 and Voyager spacecraft in 1973 and 1980, respectively; and by the Cassini and New Horizons spacecraft more recently. Until the recent arrival of Juno, only the Galileo spacecraft has ever gone into orbit around Jupiter, and it was crashed into the planet in 2003 to prevent it from contaminating one of Jupiter’s icy moons.

*Illustration of Jupiter and the Galilean satellites. Credit: NASA*

In short, Jupiter is massive and has massive storms. But compared to the planets of the inner Solar System, is it significantly less dense. Jupiter also has the most moons in the Solar System, with 67 confirmed and named moons orbiting it. But it is estimated that as many as 200 natural satellites may exist around the planet. Little wonder why this planet is named after the king of the gods.

Saturn:

Saturn is the second largest planet in the Solar System. With a mean radius of 58232±6 km, it is approximately 9.13 times the size of Earth. And at 5.6846×10²⁶ kg, it is roughly 95.15 as massive. However, since it is a gas giant, it has significantly greater volume – 8.2713×10¹⁴ km³, which is equivalent to 763.59 Earths.

The sixth most distant planet, Saturn orbits the Sun at an average distance of 9 AU (1.4 billion km; 869.9 million miles). Due to its slight eccentricity, the perihelion and aphelion distances are 9.022 (1,353.6 million km; 841.3 million mi) and 10.053 AU (1,513,325,783 km; 940.13 million mi), on average respectively.

With an average orbital speed of 9.69 km/s, it takes Saturn 10,759 Earth days to complete a single revolution of the Sun. In other words, a single Cronian year is the equivalent of about 29.5 Earth years. However, as with Jupiter, Saturn’s visible features rotate at different rates depending on latitude, and multiple rotation periods have been assigned to various regions.

This portrait looking down on Saturn and its rings was created from images obtained by NASA's Cassini spacecraft on Oct. 10, 2013. Credit: NASA/JPL-Caltech/Space Science Institute/G. Ugarkovic — *This portrait looking down on Saturn and its rings was created from images obtained by NASA’s Cassini spacecraft on Oct. 10th, 2013. Credit: NASA/JPL-Caltech/Space Science Institute/G. Ugarkovic*

As a gas giant, Saturn is predominantly composed of hydrogen and helium gas. With a mean density of 0.687 g/cm³, Saturn is the only planet in the Solar System that is less dense than water; which means that it lacks a definite surface, but is believed to have a solid core. This is due to the fact that Saturn’s temperature, pressure, and density all rise steadily toward the core.

Standard planetary models suggest that the interior of Saturn is similar to that of Jupiter, having a small rocky core surrounded by hydrogen and helium with trace amounts of various volatiles. This core is similar in composition to the Earth, but more dense due to the presence of metallic hydrogen, which as a result of the extreme pressure.

As a gas giant, the outer atmosphere of Saturn contains 96.3% molecular hydrogen and 3.25% helium by volume. Trace amounts of ammonia, acetylene, ethane, propane, phosphine and methane have been also detected in Saturn’s atmosphere. Like Jupiter, it also has a banded appearance, but Saturn’s bands are much fainter and wider near the equator.

On occasion, Saturn’s atmosphere exhibits long-lived ovals that are thousands of km wide, similar to what is commonly observed on Jupiter. Whereas Jupiter has the Great Red Spot, Saturn periodically has what’s known as the Great White Spot (aka. Great White Oval). This unique but short-lived phenomenon occurs once every Saturnian year, roughly every 30 Earth years, around the time of the northern hemisphere’s summer solstice.

The huge storm churning through the atmosphere in Saturn's northern hemisphere overtakes itself as it encircles the planet in this true-color view from NASA’s Cassini spacecraft. Image credit: NASA/JPL-Caltech/SSI — The huge storm churning through the atmosphere in Saturn’s northern hemisphere overtakes itself as it encircles the planet in this true-color view from NASA’s Cassini spacecraft. Image credit: NASA/JPL-Caltech/SSI

The persisting hexagonal wave pattern around the north pole was first noted in the Voyager images. The sides of the hexagon are each about 13,800 km (8,600 mi) long (which is longer than the diameter of the Earth) and the structure rotates with a period of 10h 39m 24s, which is assumed to be equal to the period of rotation of Saturn’s interior.

The south pole vortex, meanwhile, was first observed using the Hubble Space Telescope. These images indicated the presence of a jet stream, but not a hexagonal standing wave. These storms are estimated to be generating winds of 550 km/h, are comparable in size to Earth, and believed to have been going on for billions of years. In 2006, the Cassini space probe observed a hurricane-like storm that had a clearly defined eye. Such storms had not been observed on any planet other than Earth – even on Jupiter.

Of course, the most amazing feature of Saturn is its rings. These are made of particles of ice ranging in size from a grains of sand to the size of a car. Some scientists think the rings are only a few hundred million years old, while others think they could be as old as the Solar System itself.

Saturn has been visited by spacecraft 4 times: Pioneer 11, Voyager 1 and 2 were just flybys, but Cassini has actually gone into orbit around Saturn and has captured thousands of images of the planet and its moons. And speaking of moons, Saturn has a total of 62 moons discovered (so far), though estimates indicate that it might have as many as 150.

*A collage of Saturn (bottom left) and some of its moons: Titan, Enceladus, Dione, Rhea and Helene. Credit: NASA/JPL/Space Science Institute*

So like Jupiter, Saturn is a massive gas giant that experiences some very interesting weather patterns. It also has lots of moons and has a very low density. But what really makes Saturn stand out is its impressive ring system. Whereas every gas and ice giant has one, Saturn’s is visible to the naked eye and very beautiful to behold!

Uranus:

Next comes Uranus, the seventh planet from the Sun. With a mean radius of approximately 25,360 km and a mass of 8.68 × 10²⁵ kg, Uranus is approximately 4 times the sizes of Earth and 63 times its volume. However, as a gas giant, its density (1.27 g/cm³) is significantly lower; hence, it is only 14.5 as massive as Earth.

The variation of Uranus’ distance from the Sun is also greater than that any other planet (not including dwarf planets or plutoids). Essentially, the gas giant’s distance from the Sun varies from 18.28 AU (2,735,118,100 km) at perihelion to 20.09 AU (3,006,224,700 km) at aphelion. At an average distance of 3 billion km from the Sun, it takes Uranus roughly 84 years (or 30,687 days) to complete a single orbit of the Sun.

The standard model of Uranus’s structure is that it consists of three layers: a rocky (silicate/iron–nickel) core in the center, an icy mantle in the middle and an outer envelope of gaseous hydrogen and helium. Much like Jupiter and Saturn, hydrogen and helium account for the majority of the atmosphere – approximately 83% and 15% – but only a small portion of the planet’s overall mass (0.5 to 1.5 Earth masses).

Uranus as seen through the automated eyes of Voyager 2 in 1986. (Credit: NASA/JPL). — *Uranus as seen through the automated eyes of Voyager 2 in 1986. (Credit: NASA/JPL)*

The third most abundant element is methane ice (CH⁴), which accounts for 2.3% of its composition and which accounts for the planet’s aquamarine or cyan coloring. Trace amounts of various hydrocarbons are also found in the stratosphere of Uranus, which are thought to be produced from methane and ultraviolent radiation-induced photolysis. They include ethane (C₂H₆), acetylene (C₂H₂), methylacetylene (CH₃C₂H), and diacetylene (C₂HC₂H).

In addition, spectroscopy has uncovered carbon monoxide and carbon dioxide in Uranus’ upper atmosphere, as well as the presence icy clouds of water vapor and other volatiles, such as ammonia and hydrogen sulfide. Because of this, Uranus and Neptune are considered a distinct class of giant planet – known as “Ice Giants” – since they are composed mainly of heavier volatile substances.

The rotational period of the interior of Uranus is 17 hours, 14 minutes. As with all giant planets, its upper atmosphere experiences strong winds in the direction of rotation. Hence its weather systems are also broken up into bands that rotate around the planet, which are driven by internal heat rising to the upper atmosphere.

As a result, winds on Uranus can reach up to 900 km/h (560 mph), creating massive storms like the one spotted by the Hubble Space Telescope in 2012. Similar to Jupiter’s Great Red Spot, this “Dark Spot” was a giant cloud vortex that measured 1,700 kilometers by 3,000 kilometers (1,100 miles by 1,900 miles).

*Huge storms on Uranus were spotted by the Keck Observatory on Aug. 5 and Aug. 6, 2014. Credit: Imke de Pater (UC Berkeley), Pat Fry (University of Wisconsin), Keck Observatory*

One unique feature of Uranus is that it rotates on its side. Whereas all of the Solar System’s planets are tilted on their axes to some degree, Uranus has the most extreme axial tilt of 98°. This leads to the radical seasons that the planet experiences, not to mention an unusual day-night cycle at the poles. At the equator, Uranus experiences normal days and nights; but at the poles, each experience 42 Earth years of day followed by 42 years of night.

Uranus was the first planet to be discovered with a telescope; it was first recognized as a planet in 1781 by William Herschel. Beyond Earth-based observations, only one spacecraft (Voyager 2) has ever studied Uranus up close. It passed by the planet in 1986, and captured the first close images. Uranus has 27 known moons.

Uranus’ special nature comes through in its natural beauty, its intense weather, its ring system and its impressive array of moons. And it’s compositions, being an “ice” giant, is what gives its aquamarine color. But perhaps mist interesting is its sideways rotation, which is unique among the Solar planets.

Neptune:

Neptune is the 8th and final planet in the Solar System, orbiting the Sun at a distance of 29.81 AU (4.459 x 10⁹ km) at perihelion and 30.33 AU (4.537 x 10⁹ km) at aphelion. With a mean radius of 24,622 ± 19 km, Neptune is the fourth largest planet in the Solar System and four times as large as Earth. But with a mass of 1.0243×10²⁶ kg – which is roughly 17 times that of Earth – it is the third most massive, outranking Uranus.

Neptune takes 16 h 6 min 36 s (0.6713 days) to complete a single sidereal rotation, and 164.8 Earth years to complete a single orbit around the Sun. This means that a single day lasts 67% as long on Neptune, whereas a year is the equivalent of approximately 60,190 Earth days (or 89,666 Neptunian days).

Due to its smaller size and higher concentrations of volatiles relative to Jupiter and Saturn, Neptune (much like Uranus) is often referred to as an “ice giant” – a subclass of a giant planet. Also like Uranus, Neptune’s internal structure is differentiated between a rocky core consisting of silicates and metals; a mantle consisting of water, ammonia and methane ices; and an atmosphere consisting of hydrogen, helium and methane gas.

The core of Neptune is composed of iron, nickel and silicates, with an interior model giving it a mass about 1.2 times that of Earth. The pressure at the center is estimated to be 7 Mbar (700 GPa), about twice as high as that at the center of Earth, and with temperatures as high as 5,400 K. At a depth of 7000 km, the conditions may be such that methane decomposes into diamond crystals that rain downwards like hailstones.

Because Neptune’s axial tilt (28.32°) is similar to that of Earth (~23°) and Mars (~25°), the planet experiences similar seasonal changes. Combined with its long orbital period, this means that the seasons last for forty Earth years. Also owing to its axial tilt being comparable to Earth’s is the fact that the variation in the length of its day over the course of the year is not any more extreme than it on Earth.

*Reconstruction of Voyager 2 images showing the Great Black spot (top left), Scooter (middle), and the Small Black Spot (lower right). Credit: NASA/JPL*

Just like Jupiter and Saturn, Neptune has bands of storms that circle the planet. Astronomers have clocked winds on Neptune traveling at 2,100 km/hour, which is believed to be due to Neptune’s cold temperatures – which may decrease the friction in the system, During its 1989 flyby, NASA’s Voyager 2 spacecraft discovered the Great Dark Spot on Neptune.

Similar to Jupiter’s Great Red Spot, this is an anti-cyclonic storm measuring 13,000 km x 6,600 km across. A few years later, however, the Hubble Space Telescope failed to see the Great Dark Spot, but it did see different storms. This might mean that storms on Neptune don’t last as long as they do on Jupiter or even Saturn.

The more active weather on Neptune might be due, in part, to its higher internal heat. Although Neptune is much more distant than Uranus from the Sun, receiving 40% less sunlight, temperatures on the surface of the two planets are roughly similar. In fact, Neptune radiates 2.61 times as much energy as it receives from the Sun. This is enough heat to help drive the fastest winds in the Solar System.

Neptune is the second planet discovered in modern times. It was discovered at the same time by both Urbain Le Verrier and John Couch Adams. Neptune has only ever been visited by one spacecraft, Voyager 2, which made a fly by in August, 1989. Neptune has 13 known moons. Th largest and most famous of these is Triton, which is believed to be a former KBO that was captured by Neptune’s gravity.

*Global Color Mosaic of Triton, taken by Voyager 2 in 1989. Credit: NASA/JPL/USGS*

So much like Uranus, Neptune has a ring system, some intense weather patterns, and an impressive array of moons. Also like Uranus, Neptune’s composition allows for its aquamarine color; except that in Neptune’s case, this color is more intense and vivid. In addition, Neptune experiences some temperature anomalies that are yet to be explained. And let’s not forgt the raining diamonds!

And those are the planets in the Solar System thank you for joining the tour! Unfortunately, Pluto isn’t a planet any more, hence why it was not listed. We know, we know, take it up with the IAU!

We have written many interesting articles about the Solar System here at Universe Today. Here’s the Solar System Guide, What is the Solar System?, Interesting Facts About the Solar System, What Was Here Before the Solar System?, How Big is the Solar System?, and Is the Solar System Really a Vortex?

If you’d like more information on the Solar System, visit the Nine Planets, and Solar Views.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast.

Sources:

August 15, 2016September 26, 2016 by Evan Gough

Did Cirrus Clouds Help Keep Early Mars Warm & Wet?

Cirrus clouds in the Martian atmosphere may have helped keep Mars warm enough for liquid water to sculpt the Martian surface. Image: Mars Exploration Rover Mission, Cornell, JPL, NASA

Many features on the surface of Mars hint at the presence of liquid water in the past. These range from the Valles Marineris, a 4,000 km long and 7 km deep system of canyons, to the tiny hematite spherules called “blueberries“. These features suggest that liquid water played a vital role in shaping Mars.

Some studies show that these features have volcanic origins, but a new study from two researchers at the Carl Sagan Institute and the NASA Virtual Planet Laboratory put the focus back on liquid water. The model that the two came up with says that, if other conditions were met, cirrus clouds could have provided the necessary insulation for liquid water to flow. The two researchers, Ramses M. Ramirez and James F. Kasting, constructed a climate model to test their idea.

Cirrus clouds are thin, wispy clouds that appear regularly on Earth. They’ve also been seen on Jupiter, Saturn, Uranus, possibly Neptune, and on Mars. Cirrus clouds themselves don’t produce rain. Whatever precipitation they produce, in the form of ice crystals, evaporates before reaching the surface. The researchers behind this study focussed on cirrus clouds’ because they tend to warm the air underneath them by 10 degrees Celsius.

Cirrus clouds over Poznan, Poland. Image: Radomil, http://creativecommons.org/licenses/by-sa/3.0/

If enough of Mars was covered by cirrus clouds, then the surface would be warm enough for liquid water to flow. On Earth, cirrus clouds cover up to 25% of the Earth and have a measurable heating effect. They allow sunlight in, but absorb outgoing infrared radiation. Kasting and Ramirez sought to show how the same thing might happen on Mars, and how much cirrus cloud cover would be necessary.

The cirrus clouds themselves wouldn’t have created all the warmth. Impacts from comets and asteroids would have created the heat, and extensive cirrus cloud cover would have trapped that heat in the Martian atmosphere.

The two researchers conducted a model, called a single-column radiative-convective climate model. They then tested different ice crystal sizes, the portion of the sky covered by cirrus clouds, and the thicknesses of those clouds, to simulate different conditions on Mars.

A color mosaic of Candor Chasma (part of Mars' Valles Marineris) based on data from Voyager 1 and Voyager 2. Credit: NASA — A color mosaic of Candor Chasma (part of Mars’ Valles Marineris) based on data from Voyager 1 and Voyager 2. Credit: NASA

They found that under the right circumstances, the clouds in the early Martian atmosphere could last 4 to 5 times longer than on Earth. This favors the idea that cirrus clouds could have kept Mars warm enough for liquid water. However, they also found that 75% to 100% of the planet would have to be covered by cirrus. That amount of cloud cover seems unlikely according to the researchers, and they suggest that 50% would be more realistic. This figure is similar to Earth’s cloud cover, including all cloud types, not just cirrus.

As they adjusted the parameters of their model, they found that thicker clouds and smaller particle sizes reduced the heating effect of the cirrus cloud cover. This left a very thin set of parameters in which cirrus clouds could have kept Mars warm enough for liquid water. But their modelling also showed that there is one way that cirrus clouds could have done the job.

If the ancient Martian surface temperature was lower than 273 Kelvin, the value used in the model, then it would be possible for cirrus clouds to do their thing. And it would only have to be lower by 8 degrees Kelvin for that to happen. At times in Earth’s past, the surface temperature has been lower by 7 degrees Kelvin. The question is, might Mars have had a similarly lower temperature?

So, where does that leave us? We don’t have a definitive answer yet. It’s possible that cirrus clouds on Mars could have helped to keep the planet warm enough for liquid water. The modelling done by Ramirez and Kasting shows us what parameters were required for that to happen.

August 13, 2016February 22, 2017 by Fraser Cain

How Close Can Moons Orbit?

The Moon is great and all, but I wish it was closer. Close enough that I could see all kinds of detail on its surface without a telescope or a pair of binoculars. Close enough that I could just reach up and grab enough cheese for a lifetime of grilled cheese sandwiches.

Sure, there would be all kinds of horrible problems with having the Moon that much closer. Intense tides, a total lack of good dark nights for stargazing, and something else… Oh right, the total destruction of life on Earth. On second thought the Moon can stay right where it is, thank you very much.

The Earth’s Moon is located an average distance of 384,400 kilometers away. I say average because the Moon actually follows an elliptical orbit. At its closest point, it’s only 362,600 km, and at its furthest point, it’s 405,400 kilometers.

Still, that’s so far that it takes light a little over a second to reach the Moon, traveling almost 300,000 km/s. The Moon is far.

But what if the Moon was much closer? How close could it get and still be the Moon?

Many of the features on the moon are named as oceans. Credit: NASA — The Moon isn’t actually getting closer. It just looks that way because it’s on your computer screen. Credit: NASA

Once again, I need to remind you that this is purely theoretical. The Moon isn’t getting closer to us, in fact, it’s getting further. The Moon is slowly drifting away from us at a distance of almost 4 centimeters per year.

Let’s go back to the beginning, when the young Earth collided with a Mars-sized planet billions of years ago. This catastrophic encounter completely resurfaced planet Earth, and kicked up a massive amount of debris into orbit. Well, a Moon’s worth of debris, which collected together by mutual gravity into the roughly spherical Moon we recognize today.

Shortly after its formation, the Moon was much closer, and the Earth was spinning more rapidly. A day on Earth was only 6 hours long, and the Moon took just 17 days to orbit the Earth.

The Earth’s gravity stopped the Moon’s relative rotation, and the Moon’s gravity has been slowing the Earth’s rotation. To maintain the overall angular momentum of the system, the Moon has been drifting away to compensate.

This conservation of momentum is very important because it works both ways. As long as a moon takes longer than a day to orbit its planet, you’re going to see this same effect. The planet’s rotation slows, and the moon drifts further to compensate.

But if you have a scenario where the moon orbits faster than the planet rotates, you have the exact opposite situation. The moon makes the planet rotate more quickly, and it drifts closer to compensate. This can’t end well.

Once you get close enough, gravity becomes a harsh mistress.

Reaching the Roche limit can ruin your day. Credit: Hazmat2. Original Image Credit: Theresa Knott. CC-SA 3.0

There’s a point in all gravitational interactions called the Roche Limit. This is the point at which an object held together by gravity (like the Moon), gets close enough to another celestial body that it gets torn apart.

The exact point depends on the mass, size and density of the two objects. For example, the Roche Limit between the Earth and the Moon is about 9,500 kilometers, assuming the Moon is a solid ball. In other words, if the Moon gets within 9,500 kilometers or so, of the Earth, the gravity of the Earth overwhelms the gravity holding the Moon together.

The Moon would be torn apart, and turned into a ring. And then the pieces of the ring would continue to orbit the Earth until they all came crashing down. When that happened, it would be a series of very bad days for anyone living on Earth.

Get too close to the sun and a comet could be torn apart. Credit: NASA/JPL-Caltech

If an average comet got within about 18,000 km of Earth, it would get torn to pieces. While the Sun can, and does, tear apart comets from about 1.3 million km away.

This sounds purely theoretical, but this is actually going to happen over at Mars. Its largest moon Phobos orbits more quickly than a Martian day, which means that it’s drifting closer and closer to the planet. In a few million years, it’ll cross the Roche Limit, tear into a ring, and then all the pieces of the former Phobos will crash down onto Mars. We did a whole article on this.

Phobos, the larger of Mars' two moons, with the Stickney crater seen on the right side. Credit: HiRISE, MRO, LPL (U. Arizona), NASA — Phobos will eventually break apart from reaching the Roche limit, which will leave Deimos as Mars’ only moon. Credit: HiRISE, MRO, LPL (U. Arizona), NASA

Now you might be wondering, wait a second. I’m a separate object from the Earth, why don’t I get torn apart since I’m definitely within the Earth’s Roche Limit.

You do have gravity holding you together, but it’s insignificant compared to the chemical bonds holding you together. This is why physicists consider gravity to actually be a pretty weak force compared to all the other forces of the Universe.

You’d need to go somewhere with really intense gravity, like a black hole, for the Roche Limit to overcome the forces holding you together.

So that’s it. Bring the Moon within 9,500 kilometers or so and it would no longer be a Moon. It would be torn apart into a ring, a Halo ring, if you will, capable of wiping out all life on a planet infected by the flood. All the moons we see in the Solar System are are least at the Roche Limit or beyond, otherwise they would have broken up long ago… and probably did.

August 4, 2016September 26, 2016 by Nancy Atkinson

HiRISE Drops 1,000 Stunning New Mars Images For Your Viewing Pleasure

A possible 'Recurring Slope Lineae (RSL), dark streaks on slopes that appeared to ebb and flow over time that may or may not be caused by water on Mars. This RSL is in Ceraunius Fossae. Credit: NASA/JPL/University of Arizona.

We frequently call the HiRISE camera on board the Mars Reconnaissance Orbiter “our favorite camera” and for good reason. HiRISE, the High Resolution Imaging Science Experiment, is the largest and most powerful camera ever flown on a planetary mission, sending back incredibly beautiful, high-resolution images of Mars. While previous cameras on other Mars orbiters can identify objects about the size of a school bus, HiRISE brings it to human scale, imaging objects as small as 3 feet (1 meter) across.

The HiRISE team has just released more than 1,000 new observations of Mars for the Planetary Data System archive, showing a wide range of gullies, dunes, craters, geological layering and other features on the Red Planet. Take a look at some of the highlights (click on each image for higher resolution versions and more info):

Chloride and Paleo Dunes in Terra Sirenum. Credit: NASA/JPL/University of Arizona.

MRO orbits at about 300 km above the Martian surface. The width of a HiRISE image covers about about 6 km, with a 1.2 km strip of color in the center. The length of the images can be up to 37 km. If you click on each of these images here, or go to the HiRISE website, you can see the full images in all their glory. To fully appreciate the images, you can download the special HiView application, which allows you to see the images in various formats.

Dunes Within Arkhangelsky Crater. Credit: NASA/JPL/University of Arizona

HiRISE has been nicknamed “The People’s Camera“ because the team allows the public to choose specific targets for the camera to image. Check out the HiWISH page here if you’d like a certain spot on Mars imaged.

Crater Near Hydaspis Chaos. Credit: NASA/JPL/University of Arizona.

The lead image (the link to the image on the HiRISE site is here) shows a possible recurring slope lineae (RSL), mysterious dark streaks on slopes that appeared to ebb and flow over time. They darken and appear to flow down steep slopes during warm seasons, and then fade in cooler seasons. One possibility is this is evidence of liquid water present on Mars today. Some scientists said it could be a salty, briny liquid water flowing down the slopes. But a recent analysis says the RSLs show no mineralogical evidence for abundant liquid water or its by-products, and so it might be mechanisms other than the flow of water — such as the freeze and thaw of carbon dioxide frost — as being the major drivers of recent RSLs.

Check out the full release of images from August 2016 here.

July 29, 2016September 20, 2016 by Matt Williams

NASA Estimates SpaceX 2018 Mars Mission Will Cost Only $300 Million

Artists concept for sending SpaceX Red Dragon spacecraft to land propulsively on Mars as early as 2020. Credit: SpaceX

Ever since Musk founded SpaceX is 2002, with the intention of eventually colonizing Mars, every move he has made has been the subject of attention. And for the past two years, a great deal of this attention has been focused specifically on the development of the Falcon Heavy rocket and the Dragon 2 capsule – the components with which Musk hopes to mount a lander mission to Mars in 2018.

Among other things, there is much speculation about how much this is going to cost. Given that one of SpaceX’s guiding principles is making space exploration cost-effective, just how much money is Musk hoping to spend on this important step towards a crewed mission? As it turns out, NASA produced some estimates at a recent meeting, which indicated that SpaceX is spending over $300 million on its proposed Mars mission.

These estimates were given during a NASA Advisory Council meeting, which took place in Cleveland on July 26th between members of the technology committee. During the course of the meeting, James L. Reuter – the Deputy Associate Administrator for Programs at NASA’s Space Technology Mission Directorate – provided an overview of NASA’s agreement with SpaceX, which was signed in December of 2014 and updated this past April.

*Artists concept for sending SpaceX Red Dragon spacecraft to land propulsively on Mars as early as 2018. Credit: SpaceX*

In accordance with this agreement, NASA will be providing support for the company’s plan to send an uncrewed Dragon 2 capsule (named “Red Dragon”) to Mars by May of 2018. Intrinsic to this mission is the plan to conduct a propulsive landing on Mars, which would test the Dragon 2‘s SuperDraco Descent Landing capability. Another key feature of this mission will involve using the Falcon Heavy to deploy the capsule.

The terms of this agreement do not involve the transfer of funds, but entails active collaboration that would be to the benefit parties. As Reuters indicated in his presentation, which NASA’s Office of Communications shared with Universe Today via email (and will be available on the STMD’s NASA page soon):

“Building on an existing no-funds-exchanged collaboration with SpaceX, NASA is providing technical support for the firm’s plan to attempt to land an uncrewed Dragon 2 spacecraft on Mars. This collaboration could provide valuable entry, descent and landing (EDL) data to NASA for our journey to Mars, while providing support to American industry. We have similar agreements with dozens of U.S. commercial, government, and non-profit partners.”

Further to this agreement is NASA’s commitment to a budget of $32 million over the next four years, the timetable of which were partially-illustrated in the presentation: “NASA will contribute existing agency resources already dedicated to [Entry, Descent, Landing] work, with an estimated value of approximately $32M over four years with approximately $6M in [Fiscal Year] 2016.”

Diagram showing SpaceX's planned "Red Dragon" mission to Mars. Credit: NASA/SpaceX — *Diagram showing SpaceX’s planned “Red Dragon” mission to Mars. Credit: NASA/SpaceX*

According to Article 21 of the Space Act Agreement between NASA and SpaceX, this will include providing SpaceX with: “Deep space communications and telemetry; Deep space navigation and trajectory design; Entry, descent and landing system analysis and engineering support; Mars entry aerodynamic and aerothermal database development; General interplanetary mission advice and hardware consultation; and planetary protection consultation and advice.”

For their part, SpaceX has not yet disclosed how much their Martian mission plan will cost. But according to Jeff Foust of SpaceNews, Reuter provided a basic estimate of about $300 million based on a 10 to 1 assessment of NASA’s own financial commitment: “They did talk to us about a 10-to-1 arrangement in terms of cost: theirs 10, ours 1,” said Reuter. “I think that’s in the ballpark.”

As for why NASA has chosen to help SpaceX make this mission happen, this was also spelled out in the course of the meeting. According to Reuter’s presentation: “NASA conducted a fairly high-level technical feasibility assessment and determined there is a reasonable likelihood of mission success that would be enhanced with the addition of NASA’s technical expertise.”

Such a mission would provide NASA with valuable landing data, which would prove very useful when mounting its crewed mission in the 2030s. Other items discussed included NASA-SpaceX collaborative activities for the remainder of 2016 – which involved a “[f]ocus on system design, based heavily on Dragon 2 version used for ISS crew and cargo transportation”.

*Artistic concepts of the Falcon Heavy rocket (left) and the Dragon capsule deployed on the surface of Mars (right). Credit: SpaceX*

It was also made clear that the Falcon Heavy, which SpaceX is close to completing, will serve as the launch vehicle. SpaceX intends to conduct its first flight test (Falcon Heavy Demo Flight 1) of the heavy-lifter in December of 2016. Three more test flights are scheduled to take place between 2017 and the launch of the Mars lander mission, which is still scheduled for May of 2018.

In addition to helping NASA prepare for its mission to the Red Planet, SpaceX’s progress with both the Falcon Heavy and Dragon 2 are also crucial to Musk’s long-term plan for a crewed mission to Mars – the architecture of which has yet to be announced. They are also extremely important in the development of the Mars Colonial Transporter, which Musk plans to use to create a permanent settlement on Mars.

And while $300 million is just a ballpark estimate at this juncture, it is clear that SpaceX will have to commit considerable resources to the enterprise. What’s more, people must keep in mind that this would be merely the first in a series of major commitments that the company will have to make in order to mount a crewed mission by 2024, to say nothing of building a Martian colony!

In the meantime, be sure to check out this animation of the Crew Dragon in flight:

Further Reading: NASA STMD
TOTH: SpaceNews

July 26, 2016February 14, 2017 by Matt Williams

How Far is Mars from the Sun?

The eccentricity in Mars' orbit means that it is . Credit: NASA

With the Scientific Revolution, astronomers became aware of the fact that the Earth and the other planets orbit the Sun. And thanks to Copernicus, Galileo, Kepler, and Newton, the study of their orbits was refined to the point of mathematical precision. And with the subsequent discoveries of Uranus, Neptune, Pluto and the Kuiper Belt Objects, we have come to understand just how varied the orbits of the Solar Planets are.

Consider Mars, Earth’s second-closest neighbor, and a planet that is often referred to as “Earth’s Twin”. While it has many things in common with Earth, one area in which they differ greatly is in terms of their orbits. In addition to being farther from the Sun, Mars also has a much more elliptical orbit, which results in some rather interesting variations in temperature and weather patterns.

Perihelion and Aphelion:

Mars orbits the Sun at an average distance (semi-major axis) of 228 million km (141.67 million mi), or 1.524 astronomical units (over one and a half times the distance between Earth and the Sun). However, Mars also has the second most eccentric orbit of all the planets in the Solar System (0.0934), which makes it a distant second to crazy Mercury (at 0.20563).

This means that Mars’ distance from the Sun varies between perihelion (its closest point) and aphelion (its farthest point). In short, the distance between Mars and the Sun ranges during the course of a Martian year from 206,700,000 km (128.437 million mi) at perihelion and 249,200,000 km (154.8457 million mi) at aphelion – or 1.38 AU and 1.666 AU.

Speaking of a Martian year, with an average orbital speed of 24 km/s, Mars takes the equivalent of 687 Earth days to complete a single orbit around the Sun. This means that a year on Mars is equivalent to 1.88 Earth years. Adjusted for Martian days (aka. sols) – which last 24 hours, 39 minutes, and 35 seconds – that works out to a year being 668.5991 sols long (still almost twice as long).

Mars in also the midst of a long-term increase in eccentricity. Roughly 19,000 years ago, it reached a minimum of 0.079, and will peak again at an eccentricity of 0.105 (with a perihelion distance of 1.3621 AU) in about 24,000 years. In addition, the orbit was nearly circular about 1.35 million years ago, and will be again one million years from now.

Axial Tilt:

Much like Earth, Mars also has a significantly tilted axis. In fact, with an inclination of 25.19° to its orbital plane, it is very close to Earth’s own tilt of 23.439°. This means that like Earth, Mars also experiences seasonal variations in terms of temperature. On average, the surface temperature of Mars is much colder than what we experience here on Earth, but the variation is largely the same.

. Credit and copyright: Encyclopedia Britannica — *Mars eccentric orbit and axial tilt result in considerable seasonal variations. Credit and Copyright: Encyclopedia Britannica*

All told, the average surface temperature on Mars is -46 °C (-51 °F). This ranges from a low of -143 °C (-225.4 °F), which takes place during winter at the poles; and a high of 35 °C (95 °F), which occurs during summer and midday at the equator. This means that at certain times of the year, Mars is actually warmer than certain parts of Earth.

Orbit and Seasonal Changes:

Mars’ variations in temperature and its seasonal changes are also related to changes in the planet’s orbit. Essentially, Mars’ eccentric orbit means that it travels more slowly around the Sun when it is further from it, and more quickly when it is closer (as stated in Kepler’s Three Laws of Planetary Motion).

Mars’ aphelion coincides with Spring in its northern hemisphere, which makes it the longest season on the planet – lasting roughly 7 Earth months. Summer is second longest, lasting six months, while Fall and Winter last 5.3 and just over 4 months, respectively. In the south, the length of the seasons is only slightly different.

Mars is near perihelion when it is summer in the southern hemisphere and winter in the north, and near aphelion when it is winter in the southern hemisphere and summer in the north. As a result, the seasons in the southern hemisphere are more extreme and the seasons in the northern are milder. The summer temperatures in the south can be up to 30 K (30 °C; 54 °F) warmer than the equivalent summer temperatures in the north.

Mars' south polar ice cap, seen in April 2000 by Mars Odyssey. NASA/JPL/MSSS — *Mars’ south polar ice cap, seen in April 2000 by the Mars Odyssey probe. Credit: NASA/JPL/MSSS*

It also snows on Mars. In 2008, NASA’s Phoenix Lander found water ice in the polar regions of the planet. This was an expected finding, but scientists were not prepared to observe snow falling from clouds. The snow, combined with soil chemistry experiments, led scientists to believe that the landing site had a wetter and warmer climate in the past.

And then in 2012, data obtained by the Mars Reconnaissance Orbiter revealed that carbon-dioxide snowfalls occur in the southern polar region of Mars. For decades, scientists have known that carbon-dioxide ice is a permanent part of Mars’ seasonal cycle and exists in the southern polar caps. But this was the first time that such a phenomena was detected, and it remains the only known example of carbon-dioxide snow falling anywhere in our solar system.

In addition, recent surveys conducted by the Mars Reconnaissance Orbiter, the Mars Science Laboratory, the Mars Orbiter Mission (MOM), the Mars Atmosphere and Volatile Evolution (MAVEN) and the Opportunity and Curiosity Rovers have revealed some startling things about Mars’ deep past.

For starters, soil samples and orbital observation have demonstrated conclusively that roughly 3.7 billion years ago, the planet had more water on its surface than is currently in the Atlantic Ocean. Similarly, atmospheric studies conducted on the surface and from space have proven that Mars also had a viable atmosphere at that time, one which was slowly stripped away by solar wind.

*Scientists were able to gauge the rate of water loss on Mars by measuring the ratio of water and HDO from today and 4.3 billion years ago. Credit: Kevin Gill*

Weather Patterns:

These seasonal variations allow Mars to experience some extremes in weather. Most notably, Mars has the largest dust storms in the Solar System. These can vary from a storm over a small area to gigantic storms (thousands of km in diameter) that cover the entire planet and obscure the surface from view. They tend to occur when Mars is closest to the Sun, and have been shown to increase the global temperature.

The first mission to notice this was the Mariner 9 orbiter, which was the first spacecraft to orbit Mars in 1971, it sent pictures back to Earth of a world consumed in haze. The entire planet was covered by a dust storm so massive that only Olympus Mons, the giant Martian volcano that measures 24 km high, could be seen above the clouds. This storm lasted for a full month, and delayed Mariner 9‘s attempts to photograph the planet in detail.

And then on June 9th, 2001, the Hubble Space Telescope spotted a dust storm in the Hellas Basin on Mars. By July, the storm had died down, but then grew again to become the largest storm in 25 years. So big was the storm that amateur astronomers using small telescopes were able to see it from Earth. And the cloud raised the temperature of the frigid Martian atmosphere by a stunning 30° Celsius.

These storms tend to occur when Mars is closest to the Sun, and are the result of temperatures rising and triggering changes in the air and soil. As the soil dries, it becomes more easily picked up by air currents, which are caused by pressure changes due to increased heat. The dust storms cause temperatures to rise even further, leading to Mars’ experiencing its own greenhouse effect.

We have written many interesting articles about the distance of the planets from the Sun here at Universe Today. Here’s How Far Are the Planets from the Sun?, How Far is Mercury from the Sun?, How Far is Venus from the Sun?, How Far is the Earth from the Sun?, How Far is the Moon from the Sun?, How Far is Jupiter from the Sun?, How Far is Saturn from the Sun?, What is Uranus’ Distance from the Sun?, What is the Distance of Neptune from the Sun? and How Far is Pluto from the Sun?

For more information, Astronomy for beginners teaches you how to calculate the distance to Mars.

Finally, if you’d like to learn more about Mars in general, we have done several podcast episodes about the Red Planet at Astronomy Cast. Episode 52: Mars, and Episode 91: The Search for Water on Mars.

July 21, 2016July 23, 2016 by Matt Williams

Uh, We’re Going To Need A Bigger Landing Pad

The Falcon Heavy, once operational, will be the most powerful rocket in the world. Credit: SpaceX

Since 2000, Elon Musk been moving forward with his vision of a fleet of reusable rockets, ones that will restore domestic launch capability to the US and drastically reduce the cost of space launches. The largest rocket in this fleet is the Falcon Heavy, a variant of the Falcon 9 that uses the same rocket core, with two additional boosters that derived from the Falcon 9 first stage. When it lifts off later this year, it will be the most operational powerful rocket in the world.

More than that, SpaceX intends to make all three components of the rocket fully recoverable. This in turn will mean mean that the company is going to need some additional landing pads to recover them all. As such, the company recently announced that it is seeking federal permission to create second and third landing zones for their incoming rockets on Florida’s Space Coast.

The announcement came on Monday, July 18th, during a press conference at their facility at the Cape Canaveral Air Force Station. As they were quoted as saying by the Orlando Sentinel:

“SpaceX expects to fly Falcon Heavy for the first time later this year. We are also seeking regulatory approval to build two additional landing pads at Cape Canaveral Air Force Station. We hope to recover all three Falcon Heavy rockets, though initially we may attempt drone ship landings [at sea].”

Artist's concept of the SpaceX Red Dragon spacecraft launching to Mars on SpaceX Falcon Heavy as soon as 2018. Credit: SpaceX — Artist’s concept of the SpaceX Falcon Heavy launching in 2018. Credit: SpaceX

At present, SpaceX relies on both drone ships and their landing site at Cape Canaveral to recover rocket boosters after they return to Earth. Which option they have used depended on how high and how far downrange the rockets traveled. But with this latest announcement, they are seeking to recover all three boosters used in a single Falcon Heavy launch, which could prove to be essential down the road.

Since December, SpaceX has managed to successfully recover five Falcon 9 rockets, both at sea and on land. In fact, the announcement of their intentions to expand their landing facilities on Monday came shortly after a spent Falcon 9 returned to the company’s landing site, shortly after deploying over 2268 kg (5000 lbs) of cargo into space during a nighttime launch.

But the planned launch of the Falcon Heavy – Falcon Heavy Demo Flight 1, which is scheduled to take place this coming December – is expected to break new ground. For one, it will give the private aerospace company the ability to lift over 54 metric tons (119,000 lbs) into orbit, more the twice the payload of a Delta IV Heavy – the highest capacity rocket in service at the moment.

Chart comparing SpaceX's Falcon 9 and Falcon Heavy. Credit: SpaceX — *Chart comparing SpaceX’s Falcon 9 and Falcon Heavy. Credit: SpaceX*

Foremost among these are Elon Musk’s plans to colonize Mars. These efforts will begin in April or May of 2018 with the launch of the Dragon 2 capsule (known as the “Red Dragon”) using a Falcon Heavy. As part of an agreement with NASA to gain more information on Mars landings, the Red Dragon will send a payload to Mars that has yet to be specified.

Beyond that, the details are a bit sketchy; but Musk has indicated that he is committed to mounting a crewed mission to Mars by 2024. And if all goes well with Demo Flight 1, SpaceX expects to follow it up with Falcon Heavy Demo Flight 2 in March of 2017. This launch will see the Falcon Heavy being tested as part of the U.S. Air Force’s Evolved Expendable Launch Vehicle (EELV) certification process.

The rocket will also be carrying some important payloads, such as The Planetary Society’s LightSail 2. This 32 square-meter (344 square-foot) craft, which consists of four ultra-thin Mylar sails, will pick up where its predecessor (the LightSail 1, which was deployed in June 2015) left off – demonstrating the viability of solar sail spacecraft.

Other payloads will include NASA’s Deep Space Atomic Clock and Green Propellant Infusion Mission (GPIM), the US Air Force’s Innovative Space-based radar Antenna Technology (ISAT) satellite, the six Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC-2) satellites, and Georgia Tech’s Prox-1 nanosatellite, which will act as the LightSail 2’s parent sattelite.

Apollo 11's Saturn V rocket prior to the launch July 16, 1969. Screenshot from the 1970 documentary "Moonwalk One." Credit: NASA/Theo Kamecke/YouTube — *Apollo 11’s Saturn V rocket prior to the launch July 16, 1969. Screenshot from the 1970 documentary “Moonwalk One.” Credit: NASA/Theo Kamecke/YouTube*

The Falcon Heavy boasts three Falcon 9 engine cores, each of which is made up of 9 Merlin rocket engines. Together, these engines generate more than 2.27 million kg (5 million pounds) of thrust at liftoff, which is the equivalent of approximately eighteen 747 aircraft. Its lift capacity is also equivalent to the weight of a fully loaded 737 jetliner, complete with passengers, crew, luggage and fuel.

The Saturn V rocket – the workhorse of the Apollo Program, and which made its last flight in 1973 – is only American rocket able to deliver more payload into orbit. This is not surprising, seeing as how the Falcon Heavy was specifically designed for a new era of space exploration, one that will see humans return to the Moon, go to Mars, and eventually explore the outer Solar System.

Fingers crossed that everything works out and the Falcon Heavy proves equal to the enterprise. The year of 2024 is coming fast and many of us are eager to see boots being put to red soil! And be sure to enjoy this animation of the Falcon Heavy in flight:

Further Reading: Orlando Sentinel

July 21, 2016July 21, 2016 by Bob King

Viking: Remembering Humanity’s First Successful Mission On Mars Surface

Taken by the Viking 1 lander shortly after it touched down on Mars, this image is the first photograph ever taken from the surface of Mars. It was taken on July 20, 1976. The primary objectives of the Viking mission, which was composed of two spacecraft, were to obtain high-resolution images of the Martian surface, characterize the structure and composition of the atmosphere and surface and search for evidence of life on Mars. Credit: NASA

July 20. Sound like a familiar date? If you guessed that’s when we first set foot on the Moon 47 years ago, way to go! But it’s also the 40th anniversary of Viking 1 lander, the first American probe to successfully land on Mars.

The Russians got there first on December 2, 1971 when their Mars 3 probe touched down in the Mare Sirenum region. But transmissions stopped just 14.5 seconds later, only enough time for the crippled lander to send a partial and garbled photo that unfortunately showed no identifiable features.

The late, great Carl Sagan stands next to a model of the Viking lander. Credit: NASA

Viking 1 touched down on July 20, 1976 in Chryse Planitia, a smooth, circular plain in Mars’ northern equatorial region and operated for six years, far beyond the original 90 day mission. Its twin, Viking 2, landed about 4,000 miles (6,400 km) away in the vast northern plain called Utopia Planitia several weeks later on September 3. Both were packaged inside orbiters that took pictures of the landing sites before dispatching the probes.

The first color photo taken of the Martian surface by the Viking 1 lander on July 21, 1976. The rock strewn landscape is a familiar one seen in photos taken by many landers since. Credit: NASA

Viking 1 was originally slated to land on July 4th to commemorate the 200th year of the founding of the United States. Some of you may remember the bicentennial celebrations underway at the time. Earlier photos taken by Mariner 9 helped mission controllers pick what they thought was a safe landing site, but when the Viking 1 orbiter arrived and took a closer look, NASA deemed it too bouldery for a safe landing, so they delayed the the probe’s arrival until a safer site could be chosen. Hence the July 20th touchdown date.

My recollection at the time was that that particular date was picked to coincide with the first lunar landing.

I’ll never forget the first photo transmitted from the surface. I had started working at the News Gazette in Champaign, Ill. earlier that year in the photo department. On July 20 I joined the wire editor, a kindly. older gent named Raleigh, at the AP Photofax machine and watched the black and white image creep line-by-line from the machine. Still damp with ink, I lifted the sodden sheet into my hands, totally absorbed. Two things stood out: how incredibly sharp the picture was and ALL THOSE ROCKS! Mars looked so different from the Moon.

The Viking 1 Lander sampling arm created a number of deep trenches as part of the surface composition and biology experiments on Mars. The digging tool on the sampling arm (at lower center) could scoop up samples of material and deposit them into the appropriate experiment. Some holes were dug deeper to study soil which was not affected by solar radiation and weathering. The trenches in this ESE looking image are in the "Sandy Flats" area of the landing site at Chryse Planitia. Credit: NASA — The Viking 1 Lander sampling arm created a number of deep trenches as part of the surface composition and biology experiments on Mars. The digging tool on the sampling arm (at lower center) could scoop up samples of material and deposit them into the appropriate experiment. Some holes were dug deeper to study soil which was not affected by solar radiation and weathering. Credit: NASA

One day later, Viking 1 returned the first color photo from the surface and continued to operate, taking photos and doing science for 2,307 days until November 11, 1982, a record not broken until May 2010 by NASA’s Opportunity rover. It would have continued humming along for who knows how much longer were it not for a faulty command sent by mission control that resulted in a permanent loss of contact.

The first Mars panorama taken in Chryse Plantia by Viking 1. Credit: NASA — The first Mars panorama taken in Chryse Plantia by Viking 1. Click to supersize. Credit: NASA

Viking 2 soldiered on until its batteries failed on April 11, 1980. Both landers characterized the Martian weather and radiation environment, scooped up soil samples and measured their elemental composition and send back lots of photos including the first Martian panoramas.

Each lander carried three instruments designed to look for chemical or biological signs of living or once-living organisms. Soil samples scooped up by the landers’ sample arms were delivered to three experiments in hopes of detecting organic compounds and gases either consumed or released by potential microbes when they were treated with nutrient solutions. The results from both landers were similar: neither suite of experiments found any organic (carbon-containing) compounds nor any definitive signs of Mars bugs.

The first color picture taken by Viking 2 on the Martian surface shows a rocky reddish surface much like that seen by Viking 1 more than 4000 miles away. Credit: NASA — The first color picture taken by Viking 2 on the Martian surface shows a rocky reddish surface much like that seen by Viking 1 more than 4,000 miles away. Credit: NASA

Not that there wasn’t some excitement. The Labeled Release experiment (LC) actually did give positive results. A nutrient solution was added to a sample of Martian soil. If it contained microbes, they would take in the nutrients and release gases. Great gobs of gas were quickly released! As if the putative Martian microbes only needed a jigger of NASA’s chicken soup to find their strength. But the complete absence of organics in the soil made scientists doubtful that life was the cause. Instead it was thought that some inorganic chemical reaction must be behind the release. Negative results from the other two experiments reinforced their pessimism.

Frost on Utopia Planitia photographed by Viking 2. Credit NASA — Frost on Utopia Planitia photographed by Viking 2. Click to visit NASA’s Viking image archive (not to miss!) Credit NASA

Fast forward to 2008 when the Phoenix lander detected strongly oxidizing perchlorates originating from the interaction of strong ultraviolet light from the Sun with soils on the planet’s surface. Since Mars lacks an ozone layer, perchlorates may not only be common but also responsible for destroying much of Mars’ erstwhile organic bounty. Other scientists have reexamined the Viking LC data in recent years and concluded just the opposite, that the gas release points to life.

A fun, “period” movie about the Viking Mission to Mars

Seems to me it’s high time we should send a new suite of experiments designed to find life. Then again, maybe we won’t have to. The Mars 202o Mission will cache Martian rocks for later pickup, so we can bring pieces of Mars back to Earth and perform experiments to our heart’s content.

July 17, 2016July 17, 2016 by Bob King

We’re Finally Sending Ears to Mars

Be patient. We'll soon be hearing from Mars. Left: Wikipedia CC BY-SA 3.0; right: NASA/JPL-Caltech

The Curiosity rover took this photo of the Martian landscape on July 12, 2016. Imagine if we could listen to it at the same time. NASA now plans to include a microphone on the upcoming Mars 2020 Mission. Credit: NASA/JPL-Caltech — The Curiosity rover took this photo of the Martian landscape on July 12, 2016. Imagine if we could hear the wind passing by. We will soon. NASA plans to include a microphone on the upcoming Mars 2020 Mission. Credit: NASA/JPL-Caltech

We all love that feeling of “being there” when it comes to missions to other planets. Juno’s arrival at Jupiter, New Horizons’ flyby of Pluto and the daily upload of raw images from the Mars Curiosity rover makes each of us an armchair explorer of alien landscapes. But there’s always been something missing. Something essential in shaping our environment — sound.

The microphone selected for the Mars 2020 Mission would be mounted It would be mounted on a tiny tube that protrudes from the warm electronics box, on the bracket that holds the window for the SuperCam instrument. Credit: S. Mauric et. all, 47th Lunar and Planetary Science Conference

NASA recently gave the go-ahead for the Mars 2020 rover that will bristle with a new suite of science instruments including a microphone. Hallelujah! Finally, we’ll get to listen to the sound of the Martian wind, the occasional whirl of dust devils, the crunch of rocks beneath the rover’s wheels and even sharp pops from laser-zapped rocks!

These photos show the microphones used in two earlier missions. Neither was ever used. On left, the Mars Descent Imager and microphone for the Phoenix lander; right, the device for the failed Mars Polar Lander. Credit: NASA/JPL-Caltech — Microphones were included on two earlier missions but never used. On left, the Mars Descent Imager and microphone for the Phoenix lander; right, the device for the failed Mars Polar Lander mission. Credit: NASA/JPL-Caltech

The staff and membership of The Planetary Society have been trying for 20 years to get a working microphone to the Red Planet. One flew aboard NASA’s Mars Polar Lander mission in 1998 but that probe crashed landed when its engine shut down prematurely during the descent phase. In 2008 the Society partnered with Malin Space Science Systems to include its next microphone in the descent imager package on the Mars Phoenix lander in 2008. While that mission was successful, the imager (along with its microphone) was turned off for fear it might cause an electrical problem with a critical landing system. Mission planners hoped it might be turned on later but whether it was a money issue or fear of shorting out other critical lander instruments, it never happened. Heartbreaking.

One sound souvenir we did get from Phoenix comes to us from the European Space Agency’s Mars which recorded the radio transmissions from the lander as it descended. The signals were then processed into audio within the range of human hearing. Give a listen, there’s a music to it.

The microphone for the upcoming Mars mission will be attached to the SuperCam, seen here in this illustration zapping a rock with its laser. Credit: NASA/JPL-Caltech — The microphone for the upcoming Mars mission will be attached to the rover’s SuperCam, seen here in this illustration zapping a rock with its laser. Credit: NASA/JPL-Caltech

The Mars 2020 mission, which is expected to launch in the summer of 2020 and land the following February, will search directly for signs of ancient Martian life as well as identify and cache samples and specimens at several locations on the surface for pick-up by later missions. The microphone would be housed with the rover’s SuperCam, a souped-up version of Curiosity’s ChemCam, which fires a laser at rocks and soils from a distance to analyze the resulting vapors for their elemental composition.

SuperCam will also shoot a laser to vaporize rocks and spectroscopy to tease out their molecular and mineral composition. The microphone would be mounted on a tube sticking out of the electronics box housing SuperCam and used for scientific purposes but I suspect for public outreach as well. One of its more intriguing uses will be to record the ‘snap’ or ‘pop’ when a rock is struck with the laser. Based on the volume of the sound, scientists can estimate the specimen’s mass.

NASA plans to land the 1-ton rover using the same sky crane method that settled Curiosity to the surface in dramatic fashion. While the rover will be busy photographing the entry, descent and landing sequence, the microphone will record the ambient sound. Synched together, this should make for one of the most compelling videos ever!

A beautiful dust devil recorded by NASA's Opportunity rover. Wouldn't it be wonderful to hear it at the same time as viewing the photo? Credit: NASA/JPL-Caltech/James Sorenson — A tall, beautiful dust devil recorded by NASA’s Opportunity rover. Wouldn’t it be wonderful to hear it at the same time as viewing the photo? Credit: NASA/JPL-Caltech/James Sorenson

The microphone will also be used to augment studies of Martian weather (the aforementioned winds and dust devils) and listen to the rover’s creaks, groans and whir of its motors as the car-sized machine rolls across the alternately sandy and rocky surface of Mars. The Planetary Society is collaborating with the SuperCam team to make the most of the microphone. Who knows what else we might hear? Exploding fireball overhead? Static electricity? Rhythmic winds? Blowing sand? Slime-slap of alien pseudopods? OK, probably not the last one, but new instruments often reveal completely unexpected phenomena.

It’s been hard as hell getting a microphone on a space mission. They’ve had to compete with other instruments considered more essential not to mention the precious space the device would take up and the burden of additional mass. Mission planners consider every fraction of a gram when building a space probe because getting it into Earth orbit and blasting it to a planet takes energy. Rockets only hold so much fuel!

Your Voice on Mars

You might wonder if Mars’ atmosphere is thick enough to carry sound. The good news is that it is, but unlike Earth’s much denser nitrogen-oxygen mix, Martian air is 100 times thinner and composed of 95% carbon dioxide. If you could snap off your helmet and talk out loud on the Red Planet, your voice would sound deeper and not travel as far. Scientists liken it to having a conversation at 100,000 feet (30,500 meters) above Earth’s surface. Check out the crazy video for a simulation.

Now that you’ve made it to the end of this story, sit back and pump up the volume. We’ll have ears on Mars soon!

Pump Up the Volume by M|A|R|R|S

June 30, 2016July 1, 2016 by Ken Kremer

Curiosity Finds Ancient Mars Likely Had More Oxygen and Was More Hospitable to Life

This scene shows NASA's Curiosity Mars rover at a location called "Windjana," where the rover found rocks containing manganese-oxide minerals, which require abundant water and strongly oxidizing conditions to form. Credits: NASA/JPL-Caltech/MSSS

New chemical science findings from NASA’s Mars rover Curiosity indicate that ancient Mars likely had a higher abundance of molecular oxygen in its atmosphere compared to the present day and was thus more hospitable to life forms, if they ever existed.

Thus the Red Planet was much more Earth-like and potentially habitable billions of years ago compared to the cold, barren place we see today.

Curiosity discovered high levels of manganese oxide minerals in rocks investigated at a location called “Windjana” during the spring of 2014.

Manganese-oxide minerals require abundant water and strongly oxidizing conditions to form.

“Researchers found high levels of manganese oxides by using a laser-firing instrument on the rover. This hint of more oxygen in Mars’ early atmosphere adds to other Curiosity findings — such as evidence about ancient lakes — revealing how Earth-like our neighboring planet once was,” NASA reported.

The newly announced results stem from results obtained from the rovers mast mounted ChemCam or Chemistry and Camera laser firing instrument. ChemCam operates by firing laser pulses and then observes the spectrum of resulting flashes of plasma to assess targets’ chemical makeup.

“The only ways on Earth that we know how to make these manganese materials involve atmospheric oxygen or microbes,” said Nina Lanza, a planetary scientist at Los Alamos National Laboratory in New Mexico, in a statement.

“Now we’re seeing manganese oxides on Mars, and we’re wondering how the heck these could have formed?”

The discovery is being published in a new paper in the American Geophysical Union’s Geophysical Research Letters. Lanza is the lead author.

The manganese oxides were found by ChemCam in mineral veins investigated at “Windjana” and are part of geologic timeline being assembled from Curiosity’s research expedition across of the floor of the Gale Crater landing site.

Scientists have been able to link the new finding of a higher oxygen level to a time when groundwater was present inside Gale Crater.

“These high manganese materials can’t form without lots of liquid water and strongly oxidizing conditions,” says Lanza.

“Here on Earth, we had lots of water but no widespread deposits of manganese oxides until after the oxygen levels in our atmosphere rose.”

The high-manganese materials were found in mineral-filled cracks in sandstones in the “Kimberley” region of the crater.

Curiosity’s Panoramic view of Mount Remarkable at ‘The Kimberley Waypoint’ where rover conducted 3rd drilling campaign inside Gale Crater on Mars. The navcam raw images were taken on Sol 603, April 17, 2014, stitched and colorized. Credit: NASA/JPL-Caltech/Ken Kremer – kenkremer.com/Marco Di Lorenzo. Featured on APOD - Astronomy Picture of the Day on May 7, 2014 — Curiosity’s Panoramic view of Mount Remarkable at ‘The Kimberley Waypoint’ where rover conducted 3rd drilling campaign inside Gale Crater on Mars. The navcam raw images were taken on Sol 603, April 17, 2014, stitched and colorized. Credit: NASA/JPL-Caltech/Ken Kremer – kenkremer.com/Marco Di Lorenzo. Featured on APOD – Astronomy Picture of the Day on May 7, 2014

High concentrations of manganese oxide minerals in Earth’s ancient past correspond to a major shift in our atmosphere’s composition from low to high oxygen atmospheric concentrations. Thus its reasonable to suggest the same thing happened on ancient Mars.

As part of the investigation, Curiosity also conducted a drill campaign at Windjana, her 3rd of the mission.

Composite photo mosaic shows deployment of NASA Curiosity rovers robotic arm and two holes after drilling into ‘Windjana’ sandstone rock on May 5, 2014, Sol 621, at Mount Remarkable as missions third drill target for sample analysis by rover’s chemistry labs. The navcam raw images were stitched together from several Martian days up to Sol 621, May 5, 2014 and colorized. Credit: NASA/JPL-Caltech/Ken Kremer - kenkremer.com/Marco Di Lorenzo — Composite photo mosaic shows deployment of NASA Curiosity rovers robotic arm and two holes after drilling into ‘Windjana’ sandstone rock on May 5, 2014, Sol 621, at Mount Remarkable as missions third drill target for sample analysis by rover’s chemistry labs. The navcam raw images were stitched together from several Martian days up to Sol 621, May 5, 2014 and colorized. Credit: NASA/JPL-Caltech/Ken Kremer – kenkremer.com/Marco Di Lorenzo

How much manganese oxide was detected and what is the meaning?

“The Curiosity rover observed high-Mn abundances (>25 wt% MnO) in fracture-filling materials that crosscut sandstones in the Kimberley region of Gale crater, Mars,” according to the AGU paper.

“On Earth, environments that concentrate Mn and deposit Mn minerals require water and highly oxidizing conditions, hence these findings suggest that similar processes occurred on Mars.”

“Based on the strong association between Mn-oxide deposition and evolving atmospheric dioxygen levels on Earth, the presence of these Mn-phases on Mars suggests that there was more abundant molecular oxygen within the atmosphere and some groundwaters of ancient Mars than in the present day.”

Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.

Ken Kremer