April 24, 2017April 8, 2018 by Matt Williams

What is the Average Surface Temperature of Mercury?

MESSENGER image of Mercury from its third flyby (NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)

Of all the planets in the Solar System, Mercury is the closest to our Sun. As such, you would think it is the hottest of all the Solar planets. But strangely enough, it is not. That honor goes to Venus, which experiences an average surface temperature of 750 K (477 °C; 890 °F). Not only that, but Mercury is also cold enough in some regions to maintain water in ice form.

Overall, Mercury experiences considerable variations in temperatures, ranging from the extremely hot to the extremely cold. All of this arises from the fact that Mercury has an extremely thin atmosphere, as well as the nature of its orbit. Whereas the side facing the Sun experiences temperatures hot enough to melt lead, the darkened areas are cold enough to freeze water.

Orbital Characteristics:

Mercury has the most eccentric orbit of any planet in the Solar System (0.205). Because of this, its distance from the Sun varies between 46 million km (29 million mi) at its closest (perihelion) to 70 million km (43 million mi) at its farthest (aphelion). And with an average orbital velocity of 47.362 km/s (29.429 mi/s), it takes Mercury a total 87.969 Earth days to complete a single orbit around the Sun.

With an average rotational speed of 10.892 km/h (6.768 mph), Mercury also takes 58.646 days to complete a single rotation. This means that Mercury has a spin-orbit resonance of 3:2, which means that it completes three rotations on its axis for every two orbits around the Sun. This does not, however, mean that three days last the same as two years on Mercury.

In fact, its high eccentricity and slow rotation mean that it takes 176 Earth days for the Sun to return to the same place in the sky (aka. a solar day), which means that one day is twice as long as a single year on Mercury. The planet also has the lowest axial tilt of any planet in the Solar System – approximately 0.027° compared to Jupiter’s 3.1°, (the second smallest). This means that there is virtually no seasonal variation in surface temperature.

Exosphere:

Another factor that affects Mercury’s surface temperatures is its extremely thin atmosphere. Mercury is essentially too hot and too small to retain anything more than a variable “exosphere”, one which is made up of hydrogen, helium, oxygen, sodium, calcium, potassium and water vapor.

The Fast Imaging Plasma Spectrometer on board MESSENGER has found that the solar wind is able to bear down on Mercury enough to blast particles from its surface into its wispy atmosphere. Credit: Carolyn Nowak/Media Academica, LLC

These trace gases have a combined atmospheric pressure of about 10^-14 bar (one-quadrillionth of Earth’s atmospheric pressure). It is believed this exosphere was formed from particles captured from the Sun, volcanic outgassing and debris kicked into orbit by micrometeorite impacts.

Surface Temperatures:

Because it lacks a viable atmosphere, Mercury has no way to retain the heat from the Sun. As a result of this and its high eccentricity, the planet experiences considerable variations in temperature between its light side and dark side. Whereas the side that faces the Sun can reach temperatures of up to 700 K (427° C; 800 °F), the side in shadow dips down to 100 K (-173° C: -279 °F).

Despite its extreme highs in temperature, the existence of water ice and even organic molecules has been confirmed on Mercury’s surface, specifically in the cratered northern polar region. Since the floors of these deep craters are never exposed to direct sunlight, temperatures there remain below the planetary average.

*View of Mercury’s north pole. based on MESSENGER probe data, showing polar deposits of water ice. Credit: NASA/JHUAPL/Carnegie/National Astronomy and Ionosphere Center, Arecibo Observatory.*

These icy regions are believed to contain about 10¹⁴–10¹⁵ kg of frozen water, and may be covered by a layer of regolith that inhibits sublimation. The origin of the ice on Mercury is not yet known, but the two most likely sources are from outgassing of water from the planet’s interior or deposition by the impacts of comets. There are thought to be craters at the south pole as well, where temperatures are similarly cold enough to sustain water in ice form.

Mercury is a planet of extremes. It has an extremely eccentric orbit, an extremely thin-atmosphere, and experiences extremely hot and cold surface temperatures. Little wonder then why there is no life on the planet (at least, that we know about!) But perhaps someday, human beings may live there, sheltered in the cratered regions and using the water ice to create a habitat.

If you’d like more information on Mercury, check out NASA’s Solar System Exploration Guide, and here’s a link to NASA’s MESSENGER Misson Page.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Mercury. Listen to it here, Episode 49: Mercury.

Sources:

April 18, 2017April 19, 2017 by Nancy Atkinson

Ride Shotgun Through the Solar System with Chris Hadfield

A scene from 'Miniverse' where Chris Hadfield travels the solar system with a Tesla. Credit: CuriosityStream.

It sounds like a space nerd’s dream come true: riding in a Tesla with former astronaut Chris Hadfield, doing a science version of Carpool Karaoke. And to top it off, you’re driving through the Solar System.

A new film out called “Miniverse” via CuriosityStream takes you on a ride through a scaled-down version of our Solar System. It’s similar to other scaled solar system models — which make the huge distances in our cosmic neighborhood a little less abstract — like the Voyage Scale Model Solar System in Washington, DC, the Sagan Planet Walk in Ithaca, New York or the Delmar Loop Planet Walk in St. Louis, Missouri.

But this is bigger. In the Miniverse, various points across the continental United States indicate scaled distances between the planets.

Here’s the trailer:

The first leg of the trip takes viewers on a journey from the Sun all the way to Mars. In the scaled down solar system, that’s only the distance from Long Island to the other side of New York City. In the sky, Mars appears over the Freedom Tower in New York, and Jupiter towers above the Lincoln Memorial.

Then later, as distances between planets stretch out, the gas giants and ice giants spread across the mid-section of the US. Even our friend Pluto appears over the Pacific Ocean off the West Coast of California.

Astronaut Chris Hadfield and astronomer Laura Danly view Pluto from Santa Monica, California, in a scene from ‘Miniverse’. Credit: CuriosityStream.

Your traveling companions are pretty awesome.

Behind the wheel for the entire adventure is the funny and engaging Chris Hadfield. He’s joined by a distinguished band of interstellar hitchhikers: famed theoretical physicist Dr. Michio Kaku, as well as Derrick Pitts, Chief Astronomer at the Franklin Institute in Philadelphia, and Dr. Laura Danly, Curator of the Griffith Observatory in Los Angeles. Along the way, Hadfield poses questions to his guests about the various bodies in our solar system.

“The big takeaway is just how vast the distances are in the solar system,” Danly told Universe Today via email. “Every time we look at a drawing of our solar system it reinforces the wrong image in our minds. In reality, the planets are small and the distances are vast. Anyone who has driven cross-country knows that those miles get very long, day after day. So Miniverse provides a visceral feeling to just how great those distances are.”

A GPS-like view of the first leg of the trip through the Miniverse. Credit: CuriosityStream.

If you already have a CuriosityStream account, you can watch the film here. If you don’t, you can take advantage of a 30-day free trial in order to watch Miniverse, and all the other great science offerings available, such as Stephen Hawking’s Universe, Brian Cox’s Wonders of Life, and other topics from astronomy observing tips to info about various missions to theoretical physics. Check it out. If you’re interested in continuing after your free trial, the ad-free streaming service costs $2.99, $5.99 and $11.99 per month for standard definition, high definition, and ultra high definition 4K respectively.

We suggested to the CuriosityStream folks of putting physical markers along this path across the US, which would really make a great cross country road trip. Come along for the ride!

April 18, 2017April 28, 2017 by Evan Gough

Ceres Prank Lands Bart Simpson In Detention For Eternity

Do you see Bart Simpson's face on these surface features on Ceres? Researchers studying the surface of the dwarf planet for evidence of the presence of ice do. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA, taken by Dawn Framing Camera

Human-kind has a long history of looking up at the stars and seeing figures and faces. In fact, there’s a word for recognizing faces in natural objects: pareidolia. But this must be the first time someone has recognized Bart Simpson’s face on an object in space.

Researchers studying landslides on the dwarf planet Ceres noticed a pattern that resembles the cartoon character. The researchers, from the Georgia Institute of Technology, are studying massive landslides that occur on the surface of the icy dwarf. Their findings are reinforcing the idea that Ceres has significant quantities of frozen water.

Dwarf planet Ceres is the largest object in the asteroid belt between Mars and Jupiter. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA, taken by Dawn Framing Camera

In a new paper in the journal Nature Geoscience, the team of scientists, led by Georgia Tech Assistant Professor and Dawn Science Team Associate Britney Schmidt, examined the surface of Ceres looking for morphologies that resemble landslides here on Earth.

Research shows us that Ceres probably has a subsurface shell that is rich with water-ice. That shell is covered by a layer of silicates. Close examination of the type, and distribution, of landslides at different latitudes adds more evidence to the sub-surface ice theory.

Ceres is pretty big. At 945 km in diameter, it’s the largest object in the asteroid belt between Mars and Jupiter. It’s big enough to be rounded by its own gravity, and it actually comprises about one third of the mass of the entire asteroid belt.

Type 1 landslides on Ceres are large and occur at higher latitudes. Image: Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA, taken by Dawn Framing Camera

The team used observations from the Dawn Framing Camera to identify three types of landslides on Ceres’ surface:

Type 1 are large, rounded features similar to glacier features in the Earth’s Arctic region. These are found mostly at high latitudes on Ceres, which is where most of the ice probably is.
Type 2 are the most common. They are thinner and longer than Type 1, and look like terrestrial avalanche deposits. They’re found mostly at mid-latitudes on Ceres. The researchers behind the study thought one of them looked like Bart Simpson’s face.
Type 3 occur mostly at low latitudes near Ceres’ equator. These are always found coming from large impact craters, and probably formed when impacts melted the sub-surface ice.

Type 3 landslides on Ceres occur at low latitudes at large craters, and form when ice is melted by impacts. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA, taken by Dawn Framing Camera

The authors of the study say that finding larger landslides further away from the equator is significant, because that’s where most of the ice is.

“Landslides cover more area in the poles than at the equator, but most surface processes generally don’t care about latitude,” said Schmidt, a faculty member in the School of Earth and Atmospheric Sciences. “That’s one reason why we think it’s ice affecting the flow processes. There’s no other good way to explain why the poles have huge, thick landslides; mid-latitudes have a mixture of sheeted and thick landslides; and low latitudes have just a few.”

Key to understanding these results is the fact that these types of processes have only been observed before on Earth and Mars. Earth, obviously, has water and ice in great abundance, and Mars has large quantities of sub-surface ice as well. “It’s just kind of fun that we see features on this small planet that remind us of those on the big planets, like Earth and Mars,” Schmidt said. “It seems more and more that Ceres is our innermost icy world.”

“These landslides offer us the opportunity to understand what’s happening in the upper few kilometers of Ceres,” said Georgia Tech Ph.D. student Heather Chilton, a co-author on the paper. “That’s a sweet spot between information about the upper meter or so provided by the GRaND (Gamma Ray and Neutron Detector) and VIR (Visible and Infrared Spectrometer) instrument data, and the tens of kilometers-deep structure elucidated by crater studies.”

It’s not just the presence of these landslides, but the frequency of them, that upholds the icy-mantle idea on Ceres. The study showed that 20% to 30% of craters on Ceres larger than 10 km have some type of landslide. The researchers say that upper layers of Ceres’ could be up to 50% ice by volume.

April 17, 2017May 6, 2020 by Matt Williams

The Orbit of Saturn. How Long is a Year on Saturn?

Every planet in the Solar System takes a certain amount of time to complete a single orbit around the Sun. Here on Earth, this period lasts 365.25 days – a period that we refer to as a year. When it comes to the other planets, we use this measurement to characterize their orbital periods. And what we have found is that on many of these planets, depending on their distance from the Sun, a year can last a very long time!

Consider Saturn, which orbits the Sun at a distance of about 9.5 AU – i.e. nine and a half times the distance between the Earth and the Sun. Because of this, the speed with which it orbits the Sun is also considerably slower. As a result, a single year on Saturn lasts an average of about twenty-nine and a half years. And during that time, some interesting changes happen for the planet’s weather systems.

Orbital Period:

Saturn orbits the Sun at an average distance (semi-major axis) of 1.429 billion km (887.9 million mi; 9.5549 AU). Because its orbit is elliptical – with an eccentricity of 0.05555 – its distance from the Sun ranges from 1.35 billion km (838.8 million mi; 9.024 AU) at its closest (perihelion) to 1.509 billion km (937.6 million mi; 10.086 AU) at its farthest (aphelion).

*A diagram showing the orbits of the outer Solar planets. Saturn’s orbit is represented in yellow Credit: NASA*

With an average orbital speed of 9.69 km/s, it takes Saturn 29.457 Earth years (or 10,759 Earth days) to complete a single revolution around the Sun. In other words, a year on Saturn lasts about as long as 29.5 years here on Earth. However, Saturn also takes just over 10 and a half hours (10 hours 33 minutes) to rotate once on its axis. This means that a single year on Saturn lasts about 24,491 Saturnian solar days.

It is because of this that what we can see of Saturn’s rings from Earth changes over time. For part of its orbit, Saturn’s rings are seen at their widest point. But as it continues on its orbit around the Sun, the angle of Saturn’s rings decreases until they disappear entirely from our point of view. This is because we are seeing them edge-on. After a few more years, our angle improves and we can see the beautiful ring system again.

Orbital Inclination and Axial Tilt:

Another interesting thing about Saturn is the fact that its axis is tilted off the plane of the ecliptic. Essentially, its orbit is inclined 2.48° relative to the orbital plane of the Earth. Its axis is also tilted by 26.73° relative to the ecliptic of the Sun, which is similar to Earth’s 23.5° tilt. The result of this is that, like Earth, Saturn goes through seasonal changes during the course of its orbital period.

*R. G. French (Wellesley College) et al., NASA, ESA, and The Hubble Heritage Team (STScI/AURA)*

Seasonal Changes:

For half of its orbit, Saturn’s northern hemisphere receives more of the Sun’s radiation than the southern hemisphere. For other half of its orbit, the situation is reversed, with the southern hemisphere receiving more sunlight than the northern hemisphere. This creates storm systems that dramatically change depending on which part of its orbit Saturn is in.

For staters, winds in the upper atmosphere can reach speeds of up to 5oo meters per second (1,600 feet per second) around the equatorial region. On occasion, Saturn’s atmosphere exhibits long-lived ovals, 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, around the time of the northern hemisphere’s summer solstice. These spots can be several thousands of kilometers wide, and have been observed on many occasions throughout the past – in 1876, 1903, 1933, 1960, and 1990.

Since 2010, a large band of white clouds called the Northern Electrostatic Disturbance have been observed, which was spotted by the Cassini space probe. Given the periodic nature of these storms, another one is expected to happen in 2020, coinciding with Saturn’s next summer in the northern hemisphere.

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

Similarly, seasonal changes affect the very large weather patterns that exist around Saturn’s northern and southern polar regions. At the north pole, Saturn experiences a hexagonal wave pattern which measures some 30,000 km (20,000 mi) in diameter, while each of it six sides measure about 13,800 km (8,600 mi). This persistent storm can reach speeds of about 322 km per hour (200 mph).

Thanks to images taken by the Cassini probe between 2012 and 2016, the storm appears to undergo changes in color (from a bluish haze to a golden-brown hue) that coincide with the approach of the summer solstice. This was attributed to an increase in the production of photochemical hazes in the atmosphere, which is due to increased exposure to sunlight.

Similarly, in the southern hemisphere, images acquired by the Hubble Space Telescope have indicated the existence of large jet stream. This storm resembles a hurricane from orbit, has a clearly defined eyewall, and can reach speeds of up to 550 km/h (~342 mph). And much like the northern hexagonal storm, the southern jet stream undergoes changes as a result of increased exposure to sunlight.

*Saturn makes a beautifully striped ornament in this natural-color image, showing its north polar hexagon and central vortex (Credit: NASA/JPL-Caltech/Space Science Institute)*

Cassini was able to captured images of the south polar region in 2007, which coincided with late fall in the southern hemisphere. At the time, the polar region was becoming increasingly “smoggy”, while the northern polar region was becoming increasingly clear. The reason for this, it was argued, was that decreases in sunlight led to the formation of methane aerosols and the creation of cloud cover.

From this, it has been surmised that the polar regions become increasingly obscured by methane clouds as their respective hemisphere approaches their winter solstice, and clearer as they approach their summer solstice. And the mid-latitudes certainly show their share of changes thanks to increases/decreases in exposure to solar radiation.

Much like the length of a single year, what we know about Saturn has a lot to do with its considerable distance from the Sun. In short, few missions have been able to study it in depth, and the length of a single year means it is difficult for a probe to witness all the seasonal changes the planet goes through. Still, what we have learned has been considerable, and also quite impressive!

If you’d like more information on Saturn, check out Hubblesite’s News Releases about Saturn. And here’s a link to the homepage of NASA’s Cassini spacecraft, which is orbiting Saturn.

We have also recorded an entire episode of Astronomy Cast that’s just about Saturn. Listen here, Episode 59: Saturn.

Sources:

April 16, 2017April 16, 2017 by Matt Williams

Who Discovered Uranus?

Uranus as seen by NASA's Voyager 2. Credit: NASA/JPL

If you’ve got really good eyesight and can find a place where the light pollution is non-existent, you might be able to see Uranus without a telescope. It’s only possible with the right conditions, and if you know exactly where to look. And for thousands of years, scholars and astronomers were doing just that. But given that it was just a tiny pinprick of light, they believed Uranus was a star.

It was not until the late 18th century that the first recorded observation that recognized Uranus as being a planet took place. This occurred on March 13th, 1781, when British astronomer Sir William Herschel observed the planet using a telescope of his own creation. From this point onwards, Uranus would be recognized as the seventh planet and the third gas giant of the Solar System.

Observations pre-18th Century:

The first recorded instance of Uranus being spotted in the night sky is believed to date back to Classical Antiquity. During the 2nd century BCE, Hipparchos – the Greek astronomer, mathematician and founder of trigonometry – apparently recorded the planet as a star in his star catalogue (completed in 129 BCE).

*William Herschel’s telescope, through which the planet Uranus was first observed. Credit: Wikipedia Commons*

This catalog was later incorporated into Ptolemy’s Almagest, which became the definitive source for Islamic astronomers and for scholars in Medieval Europe for over one-thousand years. During the 17th and 18th centuries, multiple recorded sightings were made by astronomers who also catalogued it as being a star.

This included English astronomer John Flamsteed, who in 1690 observed the star on six occasions and catalogued it as a star in the Taurus constellation (34 Tauri). During the mid-18th century, French astronomer Pierre Lemonnier made twelve recorded sightings, and also recorded it as being a star. It was not until March 13th, 1781, when William Herschel observed it from his garden house in Bath, that Uranus’ true nature began to be revealed.

Hershel’s Discovery:

On the evening in question – March 13th, 1781 – William Herschel was surveying the sky with his telescope, looking for binary stars. His first report on the object was recorded on April 26th, 1781. Initially, he described it as being a “Nebulous star or perhaps a comet”, but later settled on it being a comet since it appeared to have changed its position in the sky.

*Portrait of Sir William Herschel, by Lewis Francis Abbot (1784). Credit: Wikipedia Commons/National Portrait Gallery*

When he presented his discovery to the Royal Society, he maintained this theory, but also likened it to a planet. As was recorded in the Journal of the Royal Society and Royal Astronomical Society on the occasion of his presentation:

“The power I had on when I first saw the comet was 227. From experience I know that the diameters of the fixed stars are not proportionally magnified with higher powers, as planets are; therefore I now put the powers at 460 and 932, and found that the diameter of the comet increased in proportion to the power, as it ought to be, on the supposition of its not being a fixed star, while the diameters of the stars to which I compared it were not increased in the same ratio. Moreover, the comet being magnified much beyond what its light would admit of, appeared hazy and ill-defined with these great powers, while the stars preserved that lustre and distinctness which from many thousand observations I knew they would retain. The sequel has shown that my surmises were well-founded, this proving to be the Comet we have lately observed.”

While Herschel would continue to maintain that what he observed was a comet, his “discovery” stimulated debate in the astronomical community about what Uranus was. In time, astronomers like Johann Elert Bode would conclude that it was a planet, based on its nearly-circular orbit. By 1783, Herschel himself acknowledged that it was a planet to the Royal Society.

Naming:

As he lived in England, Herschel originally wanted to name Uranus after his patron, King George III. Specifically, he wanted to call it Georgium Sidus (Latin for “George’s Star”), or the Georgian Planet. Although this was a popular name in Britain, the international astronomy community didn’t think much of it, and wanted to follow the historical precedent of naming the planets after ancient Greek and Roman gods.

Large floor mosaic from a Roman villa in Sassoferrato, Italy (ca. 200–250 CE). Aion (Uranus), the god of eternity, stands above Tellus (Gaia) and her four children (the seasons). Credit: Wikipedia Commons/Bibi Saint-Poi

Consistent with this, Bode proposed the name Uranus in a 1782 treatise. The Latin form of Ouranos, Uranus was the grandfather of Zeus (Jupiter in the Roman pantheon), the father of Cronos (Saturn), and the king of the Titans in Greek mythology. As it was discovered beyond the orbits of Jupiter and Saturn, the name seemed highly appropriate.

In the following century, Neptune would be discovered, the last of the eight official planets that are currently recognized by the IAU. And by the 20th century, astronomers would discovery Pluto and other minor planets within the Kuiper Belt. The process of discovery has been ongoing, and will likely continue for some time to come.

We have written many articles about planetary discovery here at Universe Today. Here’s Who Discovered Mercury?, Who Discovered Venus?, Who Discovered Earth?, Who Discovered Mars?, Who Discovered Jupiter?, Who Discovered Saturn?, Who Discovered Neptune?, and Who Discovered Pluto?

Here’s an article from the Hubble educational site about the discovery of Uranus, and here’s the NASA Solar System Exploration page on Uranus.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

Sources:

April 3, 2017April 28, 2017 by Matt Williams

Mars’ Trojans Show Remains Of Ancient Planetoid

A new study led by researchers from OU indicates that the outer planets could be why Mars is significantly smaller than Earth. Credit: NASA

Trojan asteroids are a fascinating thing. Whereas the most widely known are those that orbit Jupiter (around its L4 and L5 Lagrange Points), Venus, Earth, Mars, Uranus and Neptune have populations of these asteroids as well. Naturally, these rocky objects are a focal point for a lot of scientific research, since they can tell us much about the formation and early history of the Solar System.

And now, thanks to an international team of astronomers, it has been determined that the Trojan asteroids that orbit Mars are likely the remains of a mini-planet that was destroyed by a collision billions of years ago. Their findings are detailed in a paper that will be published in The Monthly Notices of the Royal Astronomical Society later this month.

For the sake of their study, the team – which was led by Galin Borisov and Apostolos Christou of the Armagh Observatory and Planetarium in Northern Ireland, examined the composition of Marian Trojans. This consisted of using spectral data obtained by the XSHOOTER spectrograph on the Very Large Telescope (VLT) and photometric data from the National Astronomical Observatory‘s two-meter telescope, and the William Herschel Telescope.

*Diagram of Jupiter and the inner Solar System, showing the Jupiter and Martian Trojans (light green) and the Main Belt (teal). Credit: Wikipedia Commons/AndrewBuck*

Specifically, they examined two members of the Eureka family – a group of Martian Trojans located at the planet’s L5 point. It is here that eight of Mars’ nine known Trojans exist in stable orbits (the other being at L4), and which are named after the first Martian Trojan ever discovered – 5261 Eureka. Like all Trojans, the Eurekas are thought to have orbited Mars ever since the formation of the Solar System.

In fact, astronomers have suspected for some time that the Martian Trojans could be the survivors of an early generation of planetesimals from which the inner Solar System formed. As Dr. Christou told Universe Today via email:

“[The Trojan family] is unique in the Solar System, in more ways than one. Unlike every other family that exists in the Main Asteroid Belt between Mars and Jupiter, it is made up of olivine-rich asteroids. Also, the asteroids are < 2km across, much smaller than we can see at other families, basically because they are much closer to the Earth than other asteroids. Finally, it is the closest family we know to the Sun, and this has implications on how it formed in that the tiny but continuous action of sunlight may have played a role.”

After combining spectrographic and photometric data on these asteroids, the team found that they were rich in the mineral olivine – a magnesium iron silicate that is a primary component of the Earth’s mantle and (it is believed) other terrestrial planets. This was unusual find as far as asteroids go, but it was even more interesting when compared to 5261 Eureka itself – which also has an olivine-rich composition.

*The first X-ray view of Martian soil by Curiosity rover at the “Rocknest” (October 17, 2012), showing traces of feldspar, pyroxenes, and olivine. Credit: NASA/JPL-Caltech/Ames*

Given that the Eureka asteroids also have similar orbits, the team concluded that every member of this family is likely to have a common composition – and hence, a common origin. These findings could have drastic implications for both the origin of Martian Trojans, and the origin of the inner Solar System. As Dr. Christou explained:

“The presence of asteroids with exposed olivine on their surfaces constrains the sequence of events that led to Mars’ formation. Olivine forms within objects that grew large enough to differentiate into a crust, mantle and core. Therefore, these objects must have formed before Mars did and were available to participate in Mars’ formation. To expose the olivine, it is necessary to break these objects up through collisions. Our ongoing work indicates that this is unlikely to have happened after the Solar System settled down in its current configuration, therefore there must have been period of intense collisional evolution during the planet formation process.”

In other words, if Mars formed from several types of material that was mixed together, these asteroids would be samples of the original source – i.e. planetesimals. By examining these asteroids further, scientists will be able to learn more about the process through which Mars came to be and (as Christou says) help us “unscramble the Martian omelette.”

This research is also likely to reveal much about the formation of Earth and the other terrestrial planets of the Solar System. Similar efforts will be made with NASA’s upcoming Lucy mission, which is scheduled to launch in October of 2021. Between 2027 and 2033, this probe will study Jupiter’s Trojan population, obtaining information on six of the asteroid’s geology, surface features, compositions, masses and densities to learn more about their origins.

Further Reading: MNRAS, Armagh Observatory

March 31, 2017April 4, 2017 by Nancy Atkinson

Four Candidates For Planet 9 Located

Artist concept of Planet 9. Credit: NASA/JPL-Caltech.

A concentrated three-day search for a mysterious, unseen planet in the far reaches of our own solar system has yielded four possible candidates. The search for the so-called Planet 9 was part of a real-time search with a Zooniverse citizen science project, in coordination with the BBC’s Stargazing Live broadcast from the Australian National University’s Siding Spring Observatory.

A view of data from SAMI, a new multi-object integral field spectrograph at Siding Spring Observatory, which was used to look for the hypothetical Planet 9. Credit: Dilyar Barat via Twitter.

Researcher Brad Tucker from ANU, who led the effort, said about 60,000 people from around the world classified over four million objects during the three days, using data from the SkyMapper telescope at Siding Spring. He and his team said that even if none of the four candidates turn out to be the hypothetical Planet 9, the effort was scientifically valuable, helping to verify their search methods as exceptionally viable.

“We’ve detected minor planets Chiron and Comacina, which demonstrates the approach we’re taking could find Planet 9 if it’s there,” Tucker said. “We’ve managed to rule out a planet about the size of Neptune being in about 90 per cent of the southern sky out to a depth of about 350 times the distance the Earth is from the Sun.

Researchers from Australian National University pose with BBC astronomers Chris Lintott, Brian Cox and Dara O’Brien. Credit: ANU.

Last year, Caltech astronomers Mike Brown and Konstantin Batygin found indirect evidence for the existence of a large planet when they found that the orbits of several different Kuiper Belt Objects were likely being influenced by a massive body, located out beyond the orbit of Pluto, about 200 times further than the distance from the Sun to the Earth. This planet would be Neptune-sized, roughly 10 times more massive than Earth. But the search is difficult because the object is likely 1000 times fainter than Pluto.

The search has been on, with many researchers working on both new observations and sifting through old data. This recent project used archival data from the Skymapper Telescope.

“With the help of tens of thousands of dedicated volunteers sifting through hundreds of thousands of images taken by SkyMapper,” Tucker said, “we have achieved four years of scientific analysis in under three days. One of those volunteers, Toby Roberts, has made 12,000 classifications.”

Mike Brown chimed in on Twitter that he thought this concentrated search was a great idea:

@btucker22 @kbatygin @cosmos4u @BBCStargazing I would just like to say: you guys rock. We'd be thrilled if you find it!

— Mike Brown (@plutokiller) March 31, 2017

Tucker said he and his team at ANU will work to confirm whether or not the unknown space objects are Planet 9 by using telescopes at Siding Spring and around the world, and he encouraged people to continue to hunt for Planet 9 through Zooniverse project, Backyard Worlds: Planet 9.

Source: ANU

March 25, 2017April 4, 2017 by Evan Gough

Juno’s Monday Jupiter Flyby Promises New Batch of Images & Science

This image of Jupiter from the Juno probe shows an intricate dance of storms and swirls. The enhanced color image was captured on February 2nd, from only 14,500 km above the gas giant's cloud tops. Image: NASA/JPL-Caltech/SwRI/MSSS/Roman Tkachenko

Juno is only part way through its mission to Jupiter, and already we’ve seen some absolutely breathtaking images of the gas giant. On Monday, the Juno spacecraft will flyby Jupiter again. This will be the craft’s 5th flyby of the gas giant, and it’ll provide us with our latest dose of Jupiter science and images. The first 4 flybys have already exceeded our expectations.

Juno will approach to within 4,400 km of Jupiter’s cloud tops, and will travel at a speed of 207,600 km/h. During this time of closest approach, called a perijove, all of Juno’s eight science instruments will be active, along with the JunoCam.

The JunoCam is not exactly part of the science payload. It was included in the missions to help engage the public with the mission, and it appears to be doing that job well. The Junocam’s targets have been partly chosen by the public, and NASA has invited anyone who cares to to download and process raw Junocam images. You can see those results throughout this article.

This image of Jupiter’s dancing cloud tops was captured during perijove 3. Image: NASA / JPL-Caltech / SwRI / MSSS / Kootenay Nature Photos © cc nc sa

This is Juno’s 5th flyby, but only its 4th science pass. During Juno’s first encounter with Jupiter, the science instruments weren’t active. Even so, after only 3 science passes, we have learned some things about Jupiter.

“We are excited to see what new discoveries Juno will reveal.” – Scott Bolton, NASA’s Principal Investigator for the Juno Mission

“This will be our fourth science pass — the fifth close flyby of Jupiter of the mission — and we are excited to see what new discoveries Juno will reveal,” said Scott Bolton, principal investigator of Juno from the Southwest Research Institute in San Antonio. “Every time we get near Jupiter’s cloud tops, we learn new insights that help us understand this amazing giant planet.”

We’ve already learned that Jupiter’s intense magnetic fields are much more complicated than we thought. We’ve learned that the belts and zones in Jupiter’s atmosphere, which are responsible for the dazzling patterns on the cloud tops, extend much deeper into the atmosphere than we thought. And we’ve discovered that charged material expelled from Io’s volcanoes helps cause Jupiter’s auroras.

The South Pole of Jupiter, taken during perijove 3. Image: NASA / JPL-Caltech / SwRI / MSSS / Luca Fornaciari © cc nc sa

Juno has the unprecedented ability to get extremely close to Jupiter. This next flyby will bring it to within 4,400 km of the cloud tops. But to do so, Juno has to pay a price. Though the sensitive equipment on the spacecraft is protected inside a titanium vault, Jupiter’s powerful radiation belts will still take a toll on the electronics. But that’s the price Juno will pay to perform its mission.

Jupiter’s dazzle as revealed by JunoCam and Shane Drever. Image: NASA / JPL-Caltech / SwRI / MSSS / Shane Drever © cc nc sa

Other missions, like Cassini, have been measured in years, while Juno’s will be measured in orbits. And once it’s completed its final orbit, it will be sent to its destruction in Jupiter’s atmosphere.

But before that happens, there’s a lot of science to be done, and a lot of stunning images to be captured.

Here’s an interview with the man leading the Juno Mission: Understanding Juno’s Orbit: An Interview with NASA’s Scott Bolton.

Here is the page for the JunoCam: https://www.missionjuno.swri.edu/junocam

March 22, 2017April 4, 2017 by Evan Gough

SpaceX & NASA Studying 2020 Landing Sites For Dragon

An artist's illustration of SpaceX's Dragon capsule entering the Martian atmosphere. Image: SpaceX

As part of their effort to kick-start the eventual colonization of Mars, SpaceX is sending an unmanned Dragon spacecraft to Mars. Initially, that mission was set for 2018, but is now re-scheduled for 2020. Now, SpaceX says they’re working with NASA to select a suitable landing site for their first Dragon mission to Mars.

At a presentation in Texas on March 18th, Paul Wooster of SpaceX said that they have been working with scientists at NASA’s Jet Propulsion Laboratory (JPL) to identify candidate landing sites on the surface of Mars. In order to aid colonization, the sites need to be:

near the equator, for solar power
near large quantities of ice, for water
at low elevation, for better thermal conditions

But finding a site that meets those conditions is difficult.

According to SpaceNews, the study done with NASA initially recognized 4 regions in Mars’ northern hemisphere, all within 40 degrees of the equator. They are Deuteronilus Mensae, Phlegra Montes, Utopia Planitia, and Arcadia Planitia.

Deuteronilus Mensae

Deuteronilus Mensae (DM) is located between older, cratered highlands and low plains. DM shows evidence of glacial activity in its surface features. In fact, there are still glaciers there, which makes it a desirable source of ice.

Phlegra Montes

Phlegra Montes (PM) is a system of mountains on the Martian surface, over 1300 km across. It’s a complex system of basins, hills, and ridges. They are likely tectonic in origin, rather than volcanic, and the region probably contains large quantities of water ice, perhaps 20 meters below the surface.

Utopia Planitia

Utopia Planitia (UP) is the region where the Viking 2 lander set down in 1976. At 3300 km in diameter, UP is the largest impact basin in the Solar System. In 2016, NASA found a huge deposit of underground ice there. The water is estimated to be the same volume as Lake Superior.

Arcadia Planitia

Arcadia Planitia (AP) is a smooth plain containing fresh lava flows. It also has a large region that was shaped by periglacial processes. This supports the idea that ice is present just beneath the surface, making it a candidate for colonization efforts.

The image below shows the Arcadia Planitia region in relation to some of its surroundings. Colonists at AP might have a great view of Olympus Mons, the largest volcano in the Solar System.

Colonists in Arcadia Planitia (upper left in map) might have a great view of Olympus Mons.

The four areas looked suitable in images from a medium resolution camera (CTX) on the Mars Reconnaissance Orbiter (MRO). But when the High Resolution Imaging Science Experiment (HiRISE) camera on the same orbiter was used to look more closely, the first three locations appeared to be much rockier. According to SpaceNews, Wooster said ““The team at JPL has been finding that, while the areas look very flat and smooth at CTX resolution, with HiRISE images, they’re quite rocky. That’s been unfortunate in terms of the opportunities for those sites.”

The fourth area, Arcadia Planitia, is a more promising site. HiRISE images showed that it is much less rocky and could be a suitable site for the first Dragon mission to Mars.

The Dragon mission to Mars is just the first step for SpaceX. They see themselves as an interplanetary transportation company eventually. SpaceX intends to send a craft to Mars every two years, when the launch window is optimal. SpaceX says they’ll have the ability to deliver one ton of payload to the Martian surface with each Dragon mission.

Their Interplanetary Transport System (ITS) might have the capability to make it to Mars in as little as 80 days, while carrying a payload of up to 450 tons. While still in the very initial stages of design, it may eventually revolutionize our ability to colonize Mars in any meaningful or enduring way. SpaceX envisions a fleet of craft in the ITS which will constantly make the return to trip to Mars.

If that ever happens, we may look at the first Dragon mission to Arcadia Planitia, or another eventual landing site, as the first step.

March 18, 2017April 4, 2017 by Evan Gough

Get Ready For The >100 Planet Solar System

A new definition of what is a planet would mean there are at least 110 planets in our Solay System. Image Courtesy of Emily Lakdawalla of the Planetary Society, Data from NASA / JPL, JHUAPL/SwRI, SSI, and UCLA / MPS / DLR / IDA, processed by Gordan Ugarkovic, Ted Stryk, Bjorn Jonsson, Roman Tkachenko, and Emily Lakdawalla. https://creativecommons.org/licenses/by-nc-sa/3.0/

Pluto’s status as a non-planet may be coming to an end. Professor Mike Brown of Caltech ended Pluto’s planetary status in 2006. But now, Kirby Runyon, a doctoral student at Johns Hopkins University, thinks it’s time to cancel that demotion and restore it as our Solar System’s ninth planet.

Pluto’s rebirth as a planet is not just all about Pluto, though. A newer, more accurate definition of what is and what is not a planet is needed. And if Runyon and the other people on the team he leads are successful, our Solar System would have more than 100 planets, including many bodies we currently call moons. (Sorry elementary school students.)

This composite of enhanced color images of Pluto (lower right) and Charon (upper left), was taken by NASA’s New Horizons spacecraft as it passed through the Pluto system on July 14, 2015. Credits: NASA/JHUAPL/SwRI

In 2006, the International Astronomical Union (IAU) changed the definition of what a planet is. Pluto’s demotion stemmed from discoveries in the 1990’s showing that it is actually a Kuiper Belt Object (KBO). It was just the first KBO that we discovered. When Pluto was discovered by Clyde Tombaugh in 1930, and included as the ninth planet in our Solar System, we didn’t know much about the Kuiper Belt.

But in 2005, the dwarf planet Eris was discovered. It was like Pluto, but 27% more massive. This begged the question, Why Pluto and not Eris? The IAU struck a committee to look into how planets should be defined.

In 2006, the IAU had a decision to make. Either expand the definition of what is and what is not a planet to include Eris and other bodies like Ceres, or shrink the definition to omit Pluto. Pluto was demoted, and that’s the way it’s been for a decade. Just enough time to re-write text books.

But a lot has happened since then. The change to the definition of planet was hotly debated, and for some, the change should never have happened. Since the New Horizons mission arrived at Pluto, that debate has been re-opened.

A group of scientists led by Runyon has written a paper to be presented at the upcoming Lunar and Planetary Science Conference on March 20th to 24th.

“A planet is a sub-stellar mass body that has never undergone nuclear fusion…” – part of the new planetary definition proposed by Runyon and his team.

The group behind the drive to re-instate Pluto have a broader goal in mind. If the issue of whether Pluto is or is not a planet sounds a little pedantic, it’s not. As Runyon’s group says on their poster to be displayed at the upcoming conference, “Nomenclature is important as it affects how we compare, think, and communicate about objects in nature.”

Runyon’s team proposes a new definition of what is a planet, focused on the geophysics of the object: “A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has enough gravitation to be round due to hydrostatic equilibrium regardless of its orbital parameters.”

The poster highlights some key points around their new planetary definition:

Emphasizes intrinsic as opposed to extrinsic properties.
Can be paraphrased for younger students: “Round objects in space that are smaller than stars.”
The geophysical definition is already in use, taught, and included in planetological glossaries.
There’s no need to memorize all 110 planets. Teach the Solar Systems zones and why different planet types formed at different distances from the Sun.

Their proposal makes a lot of sense, but there will be people opposed to it. 110 planets is quite a change, and the new definition is a real mouthful.

“They want Pluto to be a planet because they want to be flying to a planet.” – Prof. Mike Brown, from a BBC interview, July 2015.

Mike Brown, the scientist behind Pluto’s demotion, saw this all coming when New Horizons reached the Pluto system in the Summer of 2015. In an interview with the BBC, he said “The people you hear most talking about reinstatement are those involved in the (New Horizons) mission. It is emotionally difficult for them.”

Saying that the team behind New Horizons find Pluto’s status emotionally difficult seems pretty in-scientific. In fact, their proposed new definition seems very scientific.

This image from New Horizons shows the true nature of Pluto. What for a long time was just a blurry, round, blob in space, was revealed as a geologically active planet with a seasonal atmosphere. Image: NASA/JPL/New Horizons

There may be an answer to all of this. The term “classical planets” might be of some use. That term could include our 9 familiar planets, the knowledge of which guided much of our understanding and exploration of the Solar System. But it’s a fact of science that as our understanding of something grows more detailed, our language around it has to evolve to accommodate. Look at the term planetary nebula—still in use long after we know they have nothing to do with planets—and how much confusion it causes.

“It is official without IAU approval, partly via usage.” – Runyon and team, on their new definition.

In the end, it may not matter whether the IAU is convinced by Runyon’s proposed new definition. As their poster states, “As a geophysical definition, this does not fall under the domain of the IAU, and is an alternate and parallel definition that can be used by different scientists. It is “official” without IAU approval, partly via usage.”

It may seem pointless to flip-flop back and forth about Pluto’s status as a planet. But there are sound reasons for updating definitions based on our growing knowledge. We’ll have to wait and see if the IAU agrees with that, and whether or not they adopt this new definition, and the >100 planet Solar System.

You can view Runyon and team’s poster here.
You can view Emily Lakdawalla’s image of round objects in our Solar System here.
You can read the IAU’s definition of a planet here.