Uranus Archives

February 5, 2015June 24, 2016 by Matt Williams

Which Planets Have Rings?

Planetary rings are an interesting phenomena. The mere mention of these two words tends to conjure up images of Saturn, with its large and colorful system of rings that form an orbiting disk. But in fact, several other planets in our Solar System have rings. It’s just that, unlike Saturn, their systems are less visible, and perhaps less beautiful to behold.

Thanks to exploration efforts mounted in the past few decades, which have seen space probes dispatched to the outer Solar System, we have come to understand that all the gas giants – Jupiter, Saturn, Uranus and Neptune – all have their own ring systems. And that’s not all! In fact, ring systems may be more common than previously thought…

Jupiter’s Rings:

In was not until 1979 that the rings of Jupiter were discovered when the Voyager 1 space probe conducted a flyby of the planet. They were also thoroughly investigated in the 1990s by the Galileo orbiter. Because it is composed mainly of dust, the ring system is faint and can only be observed by the most powerful telescopes, or up-close by orbital spacecraft. However, during the past twenty-three years, it has been observed from Earth numerous times, as well as by the Hubble Space Telescope.

The ring system has four main components: a thick inner torus of particles known as the “halo ring”; a relatively bright, but extremely thin “main ring”; and two wide, thick, and faint outer “gossamer rings”. These outer rings are composed of material from the moons Amalthea and Thebe and are named after these moons (i.e. the “Amalthea Ring” and “Thebe Ring”).

The main and halo rings consist of dust ejected from the moons Metis, Adrastea, and other unobserved parent bodies as the result of high-velocity impacts. Scientists believe that a ring could even exist around the moon of Himalia’s orbit, which could have been created when another small moon crashed into it and caused material to be ejected from the surface.

Saturn’s Rings:

The rings of Saturn, meanwhile, have been known for centuries. Although Galileo Galilei became the first person to observe the rings of Saturn in 1610, he did not have a powerful enough telescope to discern their true nature. It was not until 1655 that Christiaan Huygens, the Dutch mathematician and scientist, became the first person to describe them as a disk surrounding the planet.

Subsequent observations, which included spectroscopic studies by the late 19th century, confirmed that they are composed of smaller rings, each one made up of tiny particles orbiting Saturn. These particles range in size from micrometers to meters that form clumps orbiting the planet, and which are composed almost entirely of water ice contaminated with dust and chemicals.

Saturn and its rings, as seen from above the planet by the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute. Assembled by Gordan Ugarkovic. — *Saturn and its rings, as seen from above the planet by the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute/Gordan Ugarkovic*

In total, Saturn has a system of 12 rings with 2 divisions. It has the most extensive ring system of any planet in our solar system. The rings have numerous gaps where particle density drops sharply. In some cases, this due to Saturn’s Moons being embedded within them, which causes destabilizing orbital resonances to occur.

However, within the Titan Ringlet and the G Ring, orbital resonance with Saturn’s moons has a stabilizing influence. Well beyond the main rings is the Phoebe ring, which is tilted at an angle of 27 degrees to the other rings and, like Phoebe, orbits in retrograde fashion.

Uranus’ Rings:

The rings of Uranus are thought to be relatively young, at not more than 600 million years old. They are believed to have originated from the collisional fragmentation of a number of moons that once existed around the planet. After colliding, the moons probably broke up into numerous particles, which survived as narrow and optically dense rings only in strictly confined zones of maximum stability.

Uranus has 13 rings that have been observed so far. They are all very faint, the majority being opaque and only a few kilometers wide. The ring system consists mostly of large bodies 0.2 to 20 m in diameter. A few rings are optically thin and are made of small dust particles which makes them difficult to observe using Earth-based telescopes.

The labeled ring arcs of Neptune as seen in newly processed data. The image spans 26 exposures combined into a equivalent 95 minute exposure, and the ring trace and an image of the occulted planet Neptune is added for reference. (Credit: M. Showalter/SETI Institute). — *The labeled ring arcs of Neptune as seen in newly processed data. Credit: M. Showalter/SETI Institute*

Neptune’s Rings:

The rings of Neptune were not discovered until 1989 until the Voyager 2 space probe conducted a flyby of the planet. Six rings have been observed in the system, which are best described as faint and tenuous. The rings are very dark, and are likely composed by organic compounds processed by radiation, similar to that found in the rings of Uranus. Much like Uranus, and Saturn, four of Neptune’s moons orbit within the ring system.

Other Bodies:

Back in 2008, it was suggested that the magnetic effects around the Saturnian moon of Rhea may indicate that it has its own ring system. However, a subsequent study indicated that observations obtained the Cassini mission suggested that some other mechanism was responsible for the magnetic effects.

Years before the the New Horizons probe visited the system, astronomers speculated that Pluto might also have a ring system. However, after conducting its historic flyby of the system in July of 2015, the New Horizons probe did not find any evidence of a ring system. While the dwarf planet had many satellites aside from its largest (Charon), debris from around the planet has not coalesced into rings, as was theorized.

Artist's impression of the New Horizons spacecraft in orbit around Pluto (Charon is seen in the background). Credit: NASA/JPL — *Artist’s impression of the New Horizons spacecraft in orbit around Pluto (Charon is seen in the background). Credit: NASA/JPL*

The minor planet of Chariklo – an asteroid that orbits the Sun between Saturn and Uranus – also has two rings that orbit it. These are perhaps due to a collision that caused a chain of debris to form in orbit around it. The announcement of these rings was made on March 26th of 2014, and was based on observations made during a stellar occultation on June 3rd, 2013.

This was followed by findings made in 2015 that indicated that 2006 Chiron – another major Centaur – could have a ring of its own. This led to further speculation that there might be many minor planets in our Solar System that have a system of rings.

In short, four planets in our Solar System have intricate ring systems, as well as the minor planet Chariklo, and perhaps even many other smaller objects. In this sense, ring systems appear to be a lot more common in our Solar System than previously thought.

We have written many articles about planets with rings for Universe Today. Here’s an article about the composition of Saturn’s rings, and here’s an article about the planets with rings.

If you’d like more info on the planets, check out NASA’s Solar System exploration page, and here’s a link to NASA’s Solar System Simulator.

We’ve also recorded a series of episodes of Astronomy Cast about every planet in the Solar System. Start here, Episode 49: Mercury.

January 16, 2015December 23, 2015 by Matt Williams

Some of the Best Pictures of the Planets in our Solar System

The Eight Planets of our Solar System. Credit: IAU

Our Solar System is a pretty picturesque place. Between the Sun, the Moon, and the Inner and Outer Solar System, there is no shortage of wondrous things to behold. But arguably, it is the eight planets that make up our Solar System that are the most interesting and photogenic. With their spherical discs, surface patterns and curious geological formations, Earth’s neighbors have been a subject of immense fascination for astronomers and scientists for millennia.

And in the age of modern astronomy, which goes beyond terrestrial telescopes to space telescopes, orbiters and satellites, there is no shortage of pictures of the planets. But here are a few of the better ones, taken with high-resolutions cameras on board spacecraft that managed to capture their intricate, picturesque, and rugged beauty.

Mercury, as imaged by the MESSENGER spacecraft, revealing parts of the never seen by human eyes. Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington — *Mercury, as imaged by the MESSENGER spacecraft, revealing parts never before seen by human eyes. Image Credit: NASA/Johns Hopkins University/Carnegie Institution of Washington*

Named after the winged messenger of the gods, Mercury is the closest planet to our Sun. It’s also the smallest (now that Pluto is no longer considered a planet. At 4,879 km, it is actually smaller than the Jovian moon of Ganymede and Saturn’s largest moon, Titan.

Because of its slow rotation and tenuous atmosphere, the planet experiences extreme variations in temperature – ranging from -184 °C on the dark side and 465 °C on the side facing the Sun. Because of this, its surface is barren and sun-scorched, as seen in the image above provided by the MESSENGER spacecraft.

*A radar view of Venus taken by the Magellan spacecraft, with some gaps filled in by the Pioneer Venus orbiter. Credit: NASA/JPL*

Venus is the second planet from our Sun, and Earth’s closest neighboring planet. It also has the dubious honor of being the hottest planet in the Solar System. While farther away from the Sun than Mercury, it has a thick atmosphere made up primarily of carbon dioxide, sulfur dioxide and nitrogen gas. This causes the Sun’s heat to become trapped, pushing average temperatures up to as high as 460°C. Due to the presence of sulfuric and carbonic compounds in the atmosphere, the planet’s atmosphere also produces rainstorms of sulfuric acid.

Because of its thick atmosphere, scientists were unable to examine of the surface of the planet until 1970s and the development of radar imaging. Since that time, numerous ground-based and orbital imaging surveys have produced information on the surface, particularly by the Magellan spacecraft (1990-94). The pictures sent back by Magellan revealed a harsh landscape dominated by lava flows and volcanoes, further adding to Venus’ inhospitable reputation.

*Earth viewed from the Moon by the Apollo 11 spacecraft. Credit: NASA*

Earth is the third planet from the Sun, the densest planet in our Solar System, and the fifth largest planet. Not only is 70% of the Earth’s surface covered with water, but the planet is also in the perfect spot – in the center of the hypothetical habitable zone – to support life. It’s atmosphere is primarily composed of nitrogen and oxygen and its average surface temperatures is 7.2°C. Hence why we call it home.

Being that it is our home, observing the planet as a whole was impossible prior to the space age. However, images taken by numerous satellites and spacecraft – such as the Apollo 11 mission, shown above – have been some of the most breathtaking and iconic in history.

The first true-colour image of Mars from ESA’s Rosetta generated using the OSIRIS orange (red), green and blue colour filters. The image was acquired on 24 February 2007 at 19:28 CET from a distance of about 240 000 km. Credit: MPS for OSIRIS Team MPS/UPD/LAM/ IAA/ RSSD/ INTA/ UPM/ DASP/ IDA — *The first true-colour image of Mars taken by the ESA’s Rosetta spacecraft on 24 February 2007. Credit: MPS for OSIRIS Team MPS/UPD/LAM/ IAA/ RSSD/ INTA/ UPM/ DASP/ IDA*

Mars is the fourth planet from our Sun and Earth’s second closest neighbor. Roughly half the size of Earth, Mars is much colder than Earth, but experiences quite a bit of variability, with temperatures ranging from 20 °C at the equator during midday, to as low as -153 °C at the poles. This is due in part to Mars’ distance from the Sun, but also to its thin atmosphere which is not able to retain heat.

Mars is famous for its red color and the speculation it has sparked about life on other planets. This red color is caused by iron oxide – rust – which is plentiful on the planet’s surface. It’s surface features, which include long “canals”, have fueled speculation that the planet was home to a civilization.

Observations made by satellites flybys in the 1960’s (by the Mariner 3 and 4 spacecraft) dispelled this notion, but scientists still believe that warm, flowing water once existed on the surface, as well as organic molecules. Since that time, a small army of spacecraft and rovers have taken the Martian surface, and have produced some of the most detailed and beautiful photos of the planet to date.

Jupiter's Great Red Spot and Ganymede's Shadow. Image Credit: NASA/ESA/A. Simon (Goddard Space Flight Center) — *Jupiter’s Great Red Spot and Ganymede’s Shadow. Image Credit: NASA/ESA/A. Simon (Goddard Space Flight Center)*

Jupiter, the closest gas giant to our Sun, is also the largest planet in the Solar System. Measuring over 70,000 km in radius, it is 317 times more massive than Earth and 2.5 times more massive than all the other planets in our Solar System combined. It also has the most moons of any planet in the Solar System, with 67 confirmed satellites as of 2012.

Despite its size, Jupiter is not very dense. The planet is comprised almost entirely of gas, with what astronomers believe is a core of metallic hydrogen. Yet, the sheer amount of pressure, radiation, gravitational pull and storm activity of this planet make it the undisputed titan of our Solar System.

Jupiter has been imaged by ground-based telescopes, space telescopes, and orbiter spacecraft. The best ground-based picture was taken in 2008 by the ESO’s Very Large Telescope (VTL) using its Multi-Conjugate Adaptive Optics Demonstrator (MAD) instrument. However, the greatest images captured of the Jovian giant were taken during flybys, in this case by the Galileo and Cassini missions.

Saturn, the second gas giant closest to our Sun, is best known for its ring system – which is composed of rocks, dust, and other materials. All gas giants have their own system of rings, but Saturn’s system is the most visible and photogenic. The planet is also the second largest in our Solar System, and is second only to Jupiter in terms of moons (62 confirmed).

Much like Jupiter, numerous pictures have been taken of the planet by a combination of ground-based telescopes, space telescopes and orbital spacecraft. These include the Pioneer, Voyager, and most recently, Cassini spacecraft.

Uranus, seen by Voyager 2. Image credit: NASA/JPL — *Uranus, seen by Voyager 2 spacecraft. Image credit: NASA/JPL*

Another gas giant, Uranus is the seventh planet from our Sun and the third largest planet in our Solar System. The planet contains roughly 14.5 times the mass of the Earth, but it has a low density. Scientists believe it is composed of a rocky core that is surrounded by an icy mantle made up of water, ammonia and methane ice, which is itself surrounded by an outer gaseous atmosphere of hydrogen and helium.

It is for this reason that Uranus is often referred to as an “ice planet”. The concentrations of methane are also what gives Uranus its blue color. Though telescopes have captured images of the planet, only one spacecraft has even taken pictures of Uranus over the years. This was the Voyager 2 craft which performed a flyby of the planet in 1986.

Neptune from Voyager 2. Image credit: NASA/JPL

Neptune is the eight planet of our Solar System, and the farthest from the Sun. Like Uranus, it is both a gas giant and ice giant, composed of a solid core surrounded by methane and ammonia ices, surrounded by large amounts of methane gas. Once again, this methane is what gives the planet its blue color. It is also the smallest gas giant in the outer Solar System, and the fourth largest planet.

All of the gas giants have intense storms, but Neptune has the fastest winds of any planet in our Solar System. The winds on Neptune can reach up to 2,100 kilometers per hour, and the strongest of which are believed to be the Great Dark Spot, which was seen in 1989, or the Small Dark Spot (also seen in 1989). In both cases, these storms and the planet itself were observed by the Voyager 2 spacecraft, the only one to capture images of the planet.

Universe Today has many interesting articles on the subject of the planets, such as interesting facts about the planets and interesting facts about the Solar System.

If you are looking for more information, try NASA’s Solar System exploration page and an overview of the Solar System.

Astronomy Cast has episodes on all of the planets including Mercury.

December 28, 2014December 23, 2015 by Bob King

Half-Moon Makes Dramatic Pass at Uranus Tonight

The half-moon creeps up on the planet Uranus this evening. The two will be near each other all night in the constellation Pisces, but closest - less than one-third of a moon diameter apart - just before midnight (CST). The views are what you'll see in a pair of binoculars. The 4th magnitude star Delta Piscium is at top in the field. Source: Stellarium

Sunlight. Moonlight. Starlight. I saw all three for the first time in weeks yesterday. Filled with photons, I feel lighter today, less burdened. Have you been under the clouds too? Let’s hope it’s clear tonight because there’s a nice event you’ll want to see if only because it’s so effortless.

The half-moon will pass very close to the planet Uranus for skywatchers across North America this evening Sunday, Dec. 28th. Pop the rubber lens caps off those binoculars and point them at the Moon. If you look a short distance to the left you’ll notice a star-like object. That’s the planet!

Seattle, two time zones west of the Midwest, will see the two closest around 9:30 p.m. local time. Source: Stellarium

You can do this anytime it’s dark, but the later you look the better because the Moon moves eastward and closer to the planet as the hours tick by. Early in the evening, the two will be separated by a couple degrees, but around 11:30 p.m. CST (9:30 p.m. PST) when the Moon reclines in the western sky, the planet will dangle like an solitary diamond less than a third of a lunar diameter away. When closest to the Moon, Uranus may prove tricky to see in its glare. If you hide the Moon behind a chimney, roofline or power pole, you’ll find it easier to see the planet.

The farther north you live, the closer the twain will be. Skywatchers in Japan, the northeastern portion of Russia, northern Canada and Alaska will see the Moon completely hide Uranus for a time. The farther west you are, the higher the Moon will be when they conjoin. West Coast states see the pair highest when they’re closest, but everyone will get a good view.

Binocular view from the desert city of Tucson around 10:45 p.m. local time tonight. Source: Stellarium — Binocular view from the desert city of Tucson around 10:45 p.m. local time tonight. You can see that the Moon is a little farther north of the planet compared to the view from Seattle. The 1,500 miles between the two cities is enough to cause our satellite, which is relatively close to the Earth, to shift position against the background stars. Source: Stellarium

When closest, the radically different character of each world can best be appreciated in a telescope. Pump the magnification up to 150x and slide both planet and Moon into the same field of view. Uranus, a pale blue dot, wears a permanent cover of methane-laced clouds where temperatures hover around -350°F (-212°C).

Though the moon will be lower in the sky, observers in the eastern U.S. and Canada will still see planet and moon only about 1/2 degree apart before moonset. Source: Stellarium — Though the Moon will be lower in the sky in the eastern U.S. and Canada when it’s closest to Uranus, observers there will still see planet and Moon only 1/2 degree apart shortly before moonset. Source: Stellarium

The fantastically large-appearing Moon in contrast has precious little atmosphere and its sunny terrain bakes at 250°F (121°C). And just look at those craters! First-quarter phase is one of the best times for Moon viewing. The terminator or shadow-line that divides lunar day from night slices right across the middle of the lunar landscape.

Shadows cast by mountain peaks and crater rims are longest and most dramatic around this time because we look squarely down upon them. At crescent and gibbous phases, the terminator is off to one side and craters and their shadows appear scrunched and foreshortened.

The day-night line or terminator cuts across a magnificent landscape rich with craters and mountain ranges emerging from the lunar night. Several prominent lunar "seas" or maria and prominent craters are shown. Credit: Christian Legrand and Patrick Chevalley / Virtual Moon Atlas — The day-night line or terminator cuts across a magnificent landscape rich with craters and mountain ranges emerging from the lunar night. Several prominent lunar “seas” or maria and prominent craters are shown. Credit: Christian Legrand and Patrick Chevalley / Virtual Moon Atlas

Enjoy the tonight’s conjunction and consider the depth of space your view encompasses. Uranus is 1.85 billion miles (2.9 billion km) from Earth today, some 7,700 times farther away than the half-moon.

December 15, 2014April 19, 2016 by Matt Williams

What is the Average Surface Temperature of the Planets in our Solar System?

Artist's impression of the planets in our solar system, along with the Sun (at bottom). Credit: NASA

It’s is no secret that Earth is the only inhabited planet in our Solar System. All the planets besides Earth lack a breathable atmosphere for terrestrial beings, but also, many of them are too hot or too cold to sustain life. A “habitable zone” which exists within every system of planets orbiting a star. Those planets that are too close to their sun are molten and toxic, while those that are too far outside it are icy and frozen.

But at the same time, forces other than position relative to our Sun can affect surface temperatures. For example, some planets are tidally locked, which means that they have one of their sides constantly facing towards the Sun. Others are warmed by internal geological forces and achieve some warmth that does not depend on exposure to the Sun’s rays. So just how hot and cold are the worlds in our Solar System? What exactly are the surface temperatures on these rocky worlds and gas giants that make them inhospitable to life as we know it?

Mercury:

Of our eight planets, Mercury is closest to the Sun. As such, one would expect it to experience the hottest temperatures in our Solar System. However, since Mercury also has no atmosphere and it also spins very slowly compared to the other planets, the surface temperature varies quite widely.

What this means is that the side exposed to the Sun remains exposed for some time, allowing surface temperatures to reach up to a molten 465 °C. Meanwhile, on the dark side, temperatures can drop off to a frigid -184°C. Hence, Mercury varies between extreme heat and extreme cold and is not the hottest planet in our Solar System.

Venus:

That honor goes to Venus, the second closest planet to the Sun which also has the highest average surface temperatures – reaching up to 460 °C on a regular basis. This is due in part to Venus’ proximity to the Sun, being just on the inner edge of the habitability zone, but also to Venus’ thick atmosphere, which is composed of heavy clouds of carbon dioxide and sulfur dioxide.

These gases create a strong greenhouse effect which traps a significant portion of the Sun’s heat in the atmosphere and turns the planet surface into a barren, molten landscape. The surface is also marked by extensive volcanoes and lava flows, and rained on by clouds of sulfuric acid. Not a hospitable place by any measure!

Earth:

Earth is the third planet from the Sun, and so far is the only planet that we know of that is capable of supporting life. The average surface temperature here is about 14 °C, but it varies due to a number of factors. For one, our world’s axis is tilted, which means that one hemisphere is slanted towards the Sun during certain times of the year while the other is slanted away.

This not only causes seasonal changes, but ensures that places located closer to the equator are hotter, while those located at the poles are colder. It’s little wonder then why the hottest temperature ever recorded on Earth was in the deserts of Iran (70.7 °C) while the lowest was recorded in Antarctica (-89.2 °C).

Mars:

Mars’ average surface temperature is -55 °C, but the Red Planet also experiences some variability, with temperatures ranging as high as 20 °C at the equator during midday, to as low as -153 °C at the poles. On average though, it is much colder than Earth, being just on the outer edge of the habitable zone, and because of its thin atmosphere – which is not sufficient to retain heat.

In addition, its surface temperature can vary by as much as 20 °C due to Mars’ eccentric orbit around the Sun (meaning that it is closer to the Sun at certain points in its orbit than at others).

Jupiter:

Since Jupiter is a gas giant, it has no solid surface, so it has no surface temperature. But measurements taken from the top of Jupiter’s clouds indicate a temperature of approximately -145°C. Closer to the center, the planet’s temperature increases due to atmospheric pressure.

At the point where atmospheric pressure is ten times what it is on Earth, the temperature reaches 21°C, what we Earthlings consider a comfortable “room temperature”. At the core of the planet, the temperature is much higher, reaching as much as 35,700°C – hotter than even the surface of the Sun.

Saturn:

Due to its distance from the Sun, Saturn is a rather cold gas giant planet, with an average temperature of -178 °Celsius. But because of Saturn’s tilt, the southern and northern hemispheres are heated differently, causing seasonal temperature variation.

And much like Jupiter, the temperature in the upper atmosphere of Saturn is cold, but increases closer to the center of the planet. At the core of the planet, temperatures are believed to reach as high as 11,700 °C.

Uranus:

Uranus is the coldest planet in our Solar System, with a lowest recorded temperature of -224°C. Despite its distance from the Sun, the largest contributing factor to its frigid nature has to do with its core.

Much like the other gas giants in our Solar System, the core of Uranus gives off far more heat than is absorbed from the Sun. However, with a core temperature of approximately 4,737 °C, Uranus’ interior gives of only one-fifth the heat that Jupiter’s does and less than half that of Saturn.

Neptune:

With temperatures dropping to -218°C in Neptune’s upper atmosphere, the planet is one of the coldest in our Solar System. And like all of the gas giants, Neptune has a much hotter core, which is around 7,000°C.

In short, the Solar System runs the gambit from extreme cold to extreme hot, with plenty of variance and only a few places that are temperate enough to sustain life. And of all of those, it is only planet Earth that seems to strike the careful balance required to sustain it perpetually.

Universe Today has many articles on the temperature of each planet, including the temperature of Mars and the temperature of Earth.

You may also want to check out these articles on facts about the planets and an overview of the planets.

NASA has a great graphic here that compares the temperatures of all the planets in our Solar System.

Astronomy Cast has episodes on all planets including Mercury.

November 21, 2014February 9, 2021 by Fraser Cain

Weekly Space Hangout – Nov. 21, 2014: New Images of Europa

Host: Fraser Cain (@fcain)

Guests:
Morgan Rehnberg (cosmicchatter.org / @cosmic_chatter)
Brian Koberlein (@briankoberlein)
Ramin Skibba (@raminskibba)
Dave Dickinson (@astroguyz / www.astroguyz.com)

Continue reading “Weekly Space Hangout – Nov. 21, 2014: New Images of Europa”

October 25, 2014December 23, 2015 by Fraser Cain

You Could Fit All the Planets Between the Earth and the Moon

You could fit all the planets within the average distance to the Moon.

I ran into this intriguing infographic over on Reddit that claimed that you could fit all the planets of the Solar System within the average distance between the Earth and the Moon.

I’d honestly never heard this stat before, and it’s pretty amazing how well they tightly fit together.

But I thought it would be a good idea to doublecheck the math, just to be absolutely certain. I pulled my numbers from NASA’s Solar System Fact Sheets, and they’re a little different from the original infographic, but close enough that the comparison is still valid.

Planet	Average Diameter (km)
Mercury	4,879
Venus	12,104
Mars	6,771
Jupiter	139,822
Saturn	116,464
Uranus	50,724
Neptune	49,244
Total	380,008

The average distance from the Earth to the Moon is 384,400 km. And check it out, that leaves us with 4,392 km to spare.

So what could we do with the rest of that distance? Well, we could obviously fit Pluto into that slot. It’s around 2,300 km across. Which leaves us about 2,092 km to play with. We could fit one more dwarf planet in there (not Eris though, too big).

The amazing Wolfram-Alpha can make this calculation for you automatically: total diameter of the planets. Although, this includes the diameter of Earth too.

A nod to CapnTrip on Reddit for posting this.

October 10, 2014December 23, 2015 by Nancy Graziano

‘Frankenstein’ Moon: Tidal Forces From Uranus May Have Contributed to Miranda’s Bizarre Appearance

Uranus' Five Largest Moons — Uranus' five largest moons shown in increasing distance from the planet. Note there is incomplete coverage of Miranda and Ariel. Image credit: NASA/JPL

Miranda, the innermost of Uranus’ five moons, has a “Frankenstein”-like appearance: it looks as though it was pieced together from parts that didn’t quite fit together properly. Plus, it has incredibly diverse surface features including canyons up to 12 times deeper than Earth’s Grand Canyon, impact craters, cliffs, and parallel grooves called sulci.

Over the years, various hypotheses have been presented in an attempt to account for Miranda’s enigmatic appearance. First thought to be the result of a catastrophic impact, disintegration, and subsequent reassembly, scientists now believe that some of Miranda’s features might have been influenced by Uranus itself, and are the result of convection: thermally-induced resurfacing from tidal forces from the planet.

Miranda's Three Coronae — Three large, geometric-shaped features called coronae are visible on Miranda. To date, Venus and Miranda are the only bodies in our solar system on which coronae have been observed. Image Credit: NASA/JPL-Caltech

Miranda was discovered in 1948 by Gerard Kuiper. Although it is only 293 miles (471 kilometers) in diameter (approximately one-seventh that of Earth’s moon,) it has one of the strangest and most varied landscapes in our Solar System.

Central to the new research was analysis of three very large, geometric shaped features known as coronae, which are only found on one other planetary body. Coronae were first identified on Venus in 1983 by Venera 15/16 radar imaging equipment.

A leading theory about their formation has been that they form when warm, sub-surface fluids rise to the surface and form a dome. As the edges of the dome cool, the center collapses and warm fluid leak out its sides, forming a crown-like structure, or corona. Based on this premise, the question is then raised as to what mechanism/processes in Miranda’s past warmed its interior sufficiently to produce warm, sub-surface fluids that resulted in coronae formation. Scientists believe that tidal warming played an important role in the formation of the coronae, but the process by which this internal heating led to these features has remained unclear.

Extensive 3D computer simulations conducted by Brown University’s Noah P. Hammond and Amy C. Barr have produced results that are consistent with the three coronae seen on Miranda. In their paper titled, “Global Resurfacing of Uranus’s Moon Miranda by Convection,” Hammond and Barr summarize their results as follows:

“We find that convection in Miranda’s ice shell powered by tidal heating can generate the global distribution of coronae, the concentric orientation of sub-parallel ridges and troughs, and the thermal gradient implied by flexure. Models that account for the possible distribution of tidal heat ing can even match the precise locations of the coronae, after a reorientation of 60°.”

Using Saturn’s moon Enceladus as a baseline due to its similarity in size, composition, and orbital frequency to Miranda, original calculations estimate that as much as 5 GW of tidal dissipation power could be generated. Hammond and Barr’s simulation results indicate almost twice that amount of power would have been created:

“Simulations that match the thermal gradient from flexure have total power outputs of close to 10 GW , somewhat larger than the total power we predict could be generated during orbital resonance.”

Results from Hammond and Barr’s simulations provide a preliminary set of answers that strive to unlock the mysteries of Miranda’s bizarre appearance. Future simulations and studies into the complex nature of tidal heating will build upon these results to provide further insight into the enigmatic moon we call Miranda.

“Global Resurfacing of Uranus’s Moon Miranda by Convection,” was published online on 15 September 2014 in GEOLOGY, a journal of The Geological Society of America. You can read the abstract here.

May 2, 2014December 29, 2015 by Fraser Cain

Weekly Space Hangout – May 2, 2014: Gas Clouds & Photobombs

Host: Fraser Cain (@fcain)
Guests: Morgan Rehnberg (cosmicchatter.org / @cosmic_chatter), Nancy Atkinson (@Nancy_A)
Continue reading “Weekly Space Hangout – May 2, 2014: Gas Clouds & Photobombs”

May 1, 2014December 23, 2015 by Jason Major

Cassini’s View of Another Pale Blue Dot

Uranus as seen by Cassini on July 19, 2013 (NASA/JPL-Caltech/SSI)

When you hear the words “pale blue dot” you’re probably reminded of the famous quote by Carl Sagan inspired by an image of Earth as a soberingly tiny speck, as imaged by Voyager 1 on Feb. 14, 1990 from beyond the orbit of Pluto. But there’s another pale blue world in our Solar System: the ice giant Uranus, and its picture was captured much more recently by the Cassini spacecraft from orbit around Saturn on April 11, 2014.

Released today by the Cassini Imaging Team, the image above shows Uranus as a tiny blue orb shining far beyond the bright hazy bands of Saturn’s F ring.

“Do you relish the notion of being a Saturnian, and gazing out from the lofty heights of Saturn at the same planets we see here from the Earth?”
– Carolyn Porco, Cassini Imaging Team Leader

Uranus’ coloration is a result of methane high in its frigid atmosphere. According to the description on the CICLOPS site, “methane on Uranus — and its sapphire-colored sibling, Neptune — absorbs red wavelengths of incoming sunlight, but allows blue wavelengths to escape back into space, resulting in the predominantly bluish color seen here.”

This was also the first time Uranus had been imaged by the Cassini spacecraft, which has been in orbit around Saturn since 2004. In fact its ten-year orbital anniversary will come on July 1.

This image adds one more planet to the list of worlds captured on Camera by Cassini, which made headlines last fall when a glorious mosaic was released that featured a backlit Saturn in eclipse surrounded by its luminous rings, the specks of several of its moons, and the distant dots of Venus, Mars, and the Earth and Moon. Made from 141 separate exposures, the mosaic was captured on July 19, 2013 — known by many space aficionados as “the day the Earth smiled” as it was the first time the world’s population was alerted beforehand that its picture would be taken from over 900 million miles away.

Saturn — with its terrestrial spacecraft in tow — was about 28.6 AU away from Uranus when the image was acquired. That’s about 4.28 billion kilometers (2.66 billion miles). From that distance the glow of the 51,118-kilometer (31,763-mile) -wide Uranus is reduced to a mere few pixels (which required digital brightening by about 4.5x, as well.)

Read more on the Cassini Imaging Central Laboratory for Operations (CICLOPS) page here and in a news release from NASA’s JPL here.

Image credit: NASA/JPL-Caltech/SSI. Source: Carolyn Porco, CICLOPS Director

April 23, 2014May 12, 2018 by Elizabeth Howell

The Inner and Outer Planets in Our Solar System

The Solar System. Credit: spaceplace.nasa.gov

In our Solar System, astronomers often divide the planets into two groups — the inner planets and the outer planets. The inner planets are closer to the Sun and are smaller and rockier. The outer planets are further away, larger and made up mostly of gas.

The inner planets (in order of distance from the sun, closest to furthest) are Mercury, Venus, Earth and Mars. After an asteroid belt comes the outer planets, Jupiter, Saturn, Uranus and Neptune. The interesting thing is, in some other planetary systems discovered, the gas giants are actually quite close to the sun.

This makes predicting how our Solar System formed an interesting exercise for astronomers. Conventional wisdom is that the young Sun blew the gases into the outer fringes of the Solar System and that is why there are such large gas giants there. However, some extrasolar systems have “hot Jupiters” that orbit close to their Sun.

The Inner Planets:

The four inner planets are called terrestrial planets because their surfaces are solid (and, as the name implies, somewhat similar to Earth — although the term can be misleading because each of the four has vastly different environments). They’re made up mostly of heavy metals such as iron and nickel, and have either no moons or few moons. Below are brief descriptions of each of these planets based on this information from NASA.

Mercury: Mercury is the smallest planet in our Solar System and also the closest. It rotates slowly (59 Earth days) relative to the time it takes to rotate around the sun (88 days). The planet has no moons, but has a tenuous atmosphere (exosphere) containing oxygen, sodium, hydrogen, helium and potassium. The NASA MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft is currently orbiting the planet.

The terrestrial planets of our Solar System at approximately relative sizes. From left, Mercury, Venus, Earth and Mars. Credit: Lunar and Planetary Institute

Venus: Venus was once considered a twin planet to Earth, until astronomers discovered its surface is at a lead-melting temperature of 900 degrees Fahrenheit (480 degrees Celsius). The planet is also a slow rotator, with a 243-day long Venusian day and an orbit around the sun at 225 days. Its atmosphere is thick and contains carbon dioxide and nitrogen. The planet has no rings or moons and is currently being visited by the European Space Agency’s Venus Express spacecraft.

Earth: Earth is the only planet with life as we know it, but astronomers have found some nearly Earth-sized planets outside of our solar system in what could be habitable regions of their respective stars. It contains an atmosphere of nitrogen and oxygen, and has one moon and no rings. Many spacecraft circle our planet to provide telecommunications, weather information and other services.

Mars: Mars is a planet under intense study because it shows signs of liquid water flowing on its surface in the ancient past. Today, however, its atmosphere is a wispy mix of carbon dioxide, nitrogen and argon. It has two tiny moons (Phobos and Deimos) and no rings. A Mars day is slightly longer than 24 Earth hours and it takes the planet about 687 Earth days to circle the Sun. There’s a small fleet of orbiters and rovers at Mars right now, including the large NASA Curiosity rover that landed in 2012.

The Outer Planets:

The outer planets (sometimes called Jovian planets or gas giants) are huge planets swaddled in gas. They all have rings and all of plenty of moons each. Despite their size, only two of them are visible without telescopes: Jupiter and Saturn. Uranus and Neptune were the first planets discovered since antiquity, and showed astronomers the solar system was bigger than previously thought. Below are brief descriptions of each of these planets based on this information from NASA.

Jupiter: Jupiter is the largest planet in our Solar System and spins very rapidly (10 Earth hours) relative to its orbit of the sun (12 Earth years). Its thick atmosphere is mostly made up of hydrogen and helium, perhaps surrounding a terrestrial core that is about Earth’s size. The planet has dozens of moons, some faint rings and a Great Red Spot — a raging storm happening for the past 400 years at least (since we were able to view it through telescopes). NASA’s Juno spacecraft is en route and will visit there in 2016.

Saturn: Saturn is best known for its prominent ring system — seven known rings with well-defined divisions and gaps between them. How the rings got there is one subject under investigation. It also has dozens of moons. Its atmosphere is mostly hydrogen and helium, and it also rotates quickly (10.7 Earth hours) relative to its time to circle the Sun (29 Earth years). Saturn is currently being visited by the Cassini spacecraft, which will fly closer to the planet’s rings in the coming years.

Near-infrared views of Uranus reveal its otherwise faint ring system, highlighting the extent to which it is tilted. Credit: Lawrence Sromovsky, (Univ. Wisconsin-Madison), Keck Observatory.

Uranus: Uranus was first discovered by William Herschel in 1781. The planet’s day takes about 17 Earth hours and one orbit around the Sun takes 84 Earth years. Its mass contains water, methane, ammonia, hydrogen and helium surrounding a rocky core. It has dozens of moons and a faint ring system. There are no spacecraft slated to visit Uranus right now; the last visitor was Voyager 2 in 1986.

Neptune: Neptune is a distant planet that contains water, ammmonia, methane, hydrogen and helium and a possible Earth-sized core. It has more than a dozen moons and six rings. The only spacecraft to ever visit it was NASA’s Voyager 2 in 1989.

To learn more about the planets and missions, check out these links:

Solar System Exploration: Planets (NASA)
NASA Photojournal (NASA)
Missions (NASA)
Space Science (European Space Agency)
USGS Astrogeology (U.S. Geological Survey)
The Solar System And Its Planets (European Space Agency)