Tag Archives: planet

Discovery of carbon on Mercury reveals the planet’s dark past

The Conversation

Ivy Shih, The Conversation

Mercury has been found to have a dark side with graphite, a crystalline form of carbon commonly found in pencils, being the source of the mysterious dark colouration of the planet’s surface.

The study, published this week in Nature Geoscience, was led by a team from the Johns Hopkins University Applied Physics Laboratory in the US, which analysed measurements collected by NASA’s Messenger spacecraft as it went through its final orbits of Mercury.

The findings not only test theories of early planetary formation but may offer an explanation of the amount of carbon here on Earth.

Remains of a primordial crust

The surface colour of planetary bodies is often an indicator of the elements that make them up. For example, the distinctive rusty red appearance of Mars can be attributed to iron oxide.

It had previously been believed that the iron and titanium were typically responsible for the dark coloration on planetary surfaces. However, Mercury is quite dark, but lacked high enough concentrations of those elements to account for its colour.

“Mercury’s surface was significantly darker than we could account for on the basis of our understanding of Mercury’s surface chemistry,” said Dr Patrick Peplowski, from the Johns Hopkins University Applied Physics Laboratory, and lead author on the study.

“So what was causing Mercury to be so dark?”

By carefully examining data sent back to Earth by the Messenger probe, the team found that the dark colouration was due to the presence of carbon, with Mercury having high levels than any other planets or their moons.

The discovery of carbon on Mercury was an unexpected one, so much so that none of the instruments on Messenger were designed to detect the element. Instead, Peplowski and his colleagues had to use multiple instruments to identify the carbon.

Need for continued planetary exploration

The discovery gives weight to a theory on how Mercury was formed. The carbon-rich material was detected underneath younger volcanic materials that make up Mercury’s present day surface. This suggests that early Mercury’s original carbon-rich crust may have been formed from graphite that floated to the top of a global magma ocean.

These primordial “floating crusts” provide a rare perspective on early planetary formation.

“This is interesting because the original crusts of the other planets were destroyed long ago by processes like volcanic resurfacing, plate tectonics and erosion,” Peplowski told The Conversation.

“The carbon we see today may be the remains of that ancient, 4.5 billion-year-old crust.”

However, there are still questions as to how the planetary crust was originally formed and why carbon was found around some craters and not others.

“There is a lot of follow-on work to be done,” said Peplowski. “Future missions to Mercury might benefit from instrumentation specifically designed to map carbon in order to follow up on this result.”

The next planetary exploration of Mercury could provide further answers, with the European Space Agency launching the BepiColumbo probe to Mercury next year.

“It has an entirely new suite of instruments that can add to our understanding of carbon on Mercury.”

Planetary puzzles

Dr Helen Maynard-Casely, an Instrument Scientist from the Australian Nuclear Science and Technology Organisation, who was not involved in the study, said the study sheds light on some longstanding mysteries in planetary science.

She added that the theory they study suggests that how Mercury evolved shares many similarities to the early formation of the Moon.

“The early crust of the Moon was made of lighter minerals. It is thought these were stripped off the Earth. In terms of planetary formation, these minerals are like froth on a coffee. Then, as the surface of the Moon has evolved, impacts and lava flows have brought the darker material onto the faces of the Moon,” she said.

“What they’re seeing is that this darker material on Mercury is the remnants of the early frothy material. Graphite is light compared to the other materials on Mercury. They suggest this rose to the top at the very beginning of the planet’s formation creating the first crust of Mercury as it was cooling down.”

But throughout the life of Mercury in the solar system, repeated impacts had churned up the crust, leaving very little of the early surface intact.

Maynard-Casely says that the discovery came as a surprise and may change our view on the how the solar system was formed, and the current model of predicting the presence of carbon, including here on Earth.

“Carbon’s been a very tricky element to pin down, even on Earth, and it is a puzzle to discover what has happened to our carbon. There’s a thought now that a lot of the carbon on Earth is trapped further down within the interior and that we are missing a lot of minerals. There is currently a bit of a worldwide hunt for these,” she said.

“The knowledge of carbon’s significance on Mercury would bring those questions back to the forefront and reinvigorate discussions.”

The ConversationIvy Shih, Editor, The Conversation

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

 

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NASA mission brings Pluto into sharp focus – but it’s still not a planet

The Conversation

David Rothery, The Open University

The new pictures that NASA’s New Horizons probe has begun to beam back have revealed Pluto and its largest moon, Charon, in ever greater detail from what is the first ever spacecraft fly-by.

Pluto has an atmosphere and five known moons which have been glimpsed by New Horizons as it closes in, and while we can’t predict what we will find, whatever is revealed is sure to lead to renewed cries that Pluto be re-classified as a planet – a status it lost in 2006.

Two sides of Pluto (larger and browner) and Charon (smaller and greyer) seen as New Horizons approaches. NASA/John Hopkins University APL/SWRI

Pluto was embraced as the solar system’s ninth planet upon discovery by Clyde Tombaugh in 1930. He’d been looking for a planet where faulty data suggested a planet-sized body was perturbing the orbit of Neptune. This, he felt, was it – and the world agreed. Pluto’s mass was at first thought to be roughly the same as the Earth’s, but by 1948 estimates had shrunk it to the size of Mars.

When Pluto’s largest moon Charon was discovered in 1978, Charon’s orbit showed that Pluto’s mass is actually about only 0.2% of the Earth’s (one-sixth that of the Moon), and we now know that its diameter is about 2368km, or two-thirds that of the Moon.

Being so insubstantial, then, should Pluto be classed as a planet? There may seem no obvious reason why not. After all, the Earth is only 0.3% the mass of Jupiter. Planets clearly span a wide range of masses. But the main reasons why delegates to the International Astronomical Union (IAU) voted to demote Pluto from planet status are not based primarily on mass or size.

Pluto is one of many

Since the 1990s, many other roughly Pluto-sized bodies have been discovered beyond Neptune, such as Eris, Huamea and Makemake. There are more than a thousand objects now documented in what is called the Kuiper belt, a region beyond Neptune where it seems no large objects were able to form.

If Pluto had been discovered along with the others rather than 60 years earlier, there can be little doubt that no one would have called it a planet in the first place. There is nothing special about Pluto, other than the accident of having been the first to be discovered.

Eight of the so-called trans-Neptunian objects, including Pluto, and their moons. Lexicon

The crucial part of the definition of planet adopted by the IAU in 2006 is that a planet should have “cleared the neighbourhood of its own orbit”. Neptune, 8,600 times more massive than Pluto, has achieved this because neither Pluto nor anything else that crosses Neptune’s orbit comes close to rivalling Neptune’s mass. On the other hand Pluto clearly does not comply to this definition – it has rivals of comparable mass in addition to being overshadowed by the vastly more massive Neptune.

While it may be that this definition is hard to apply in other solar systems, it works for ours and is a far neater approach than including every Kuiper belt object as a planet – thousands of them, which would be ridiculous. The alternative of defining a size or mass minimum at which an object ceases to be a planet would suffer from our variable and imperfect ability to measure their size or mass remotely.

The Kuiper belt is a busy place. NASA/Johns Hopkins University APL/SRI/Alex Parker

A linguistic fudge

Nevertheless, the IAU shied away from completely stripping the Pluto of its appellation of planet by inventing a new term, dwarf planet. This denotes an object orbiting the sun that has not cleared its orbit, but which has sufficient mass for its own gravity to have pulled it into a near-spherical shape (described as hydrostatic equilibrium). This applies to Pluto, Eris and a few other Kuiper belt objects, and also to the largest asteroid, Ceres.

‘Pluto a planet, Jim? You’ve got to be kidding me.’ NBC Television

I think that was an unnecessary concession to the Pluto-is-a-planet lobby, though it proves that the IAU is not controlled by “a clique of Pluto-haters” as one astronomer has claimed. In fact it’s messy for two reasons. First, shapes cannot be precisely determined for objects that have not been visited by a spacecraft; they have to be assumed on the basis of mechanical models that could easily be wrong. Second, whereas the giant planets (Jupiter, Saturn, Uranus and Neptune) are planets, by the IAU’s own definition the dwarf planets are not planets. As Mr Spock might have said, “That’s illogical, Captain.”

Planetary scientists have a duty to describe the nature of the solar system as clearly as possible, and to lead the public to a clearer understanding of nature – irrespective of how its elements are classified. Appealing to sentiment, seeking celebrity endorsement and posting photos of presidential candidates with “Pluto is a planet” T-shirts is not a good way to advance anyone’s understanding. It’s time to let go of the past, and embrace Pluto as a fascinating world and the most interesting member of the Kuiper belt.

The ConversationDavid Rothery is Professor of Planetary Geosciences at The Open University.

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

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From Mercury to Pluto: the year ahead in planetary exploration

The Conversation

By Donna Burton, University of Southern Queensland

2015 is already shaping up to be a big year in astronomy and planetary exploration, with the best yet to come. Here are some highlights to keep your eye on throughout the year.

Opportunity

January 25 marked 11 years since the Opportunity Rover landed on Mars in 2004 just three weeks after its now inactive twin Spirit. This view is taken from the rim of the Endeavour Crater at a point known as Cape Tribulation.

Opportunity ’s view from Cape Tribulation on the rim of Endeavour Crater, January 22, 2015
NASA/JPL-Caltech/Cornell Univ./Arizona State Univ

This is the highest point that the rover Opportunity has reached since it left the Victoria Crater area back in 2008. It has taken three years for the 180kg solar powered robot to complete the journey down to the Endeavour Crater, which measures 22 kilometres in diameter.

One of its key mission accomplishments has been the characterisation of soft rocks and soil to provide evidence of past water on the Mars. Asteroid 39392 Opportunity was named after this hardworking rover.

Dawn probe

This animation of the dwarf planet Ceres was made by combining images taken by NASA’s Dawn spacecraft on January 25, 2015.
NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Later this year in March, the NASA probe Dawn will arrive at the dwarf planet Ceres. Ceres is one of the largest known bodies in the asteroid belt. It is thought that favourable conditions for life may have once existed there, and the presence of water has recently been announced.

NASA also recently released amazing results from the Dawn mission about the asteroid Vesta. This asteroid was believed to be dry, since it was believed that asteroids are incapable of retaining water.

Yet the recent results provide evidence that Vesta may have had short-lived flows of water-mobilised material on its surface. These results make the asteroid very interesting as these characteristics were thought only to be present on planets. Who knows what interesting discoveries will be made with the upcoming rendezvous with Ceres?

MESSENGER to Mercury

Alver crater graces this image of Mercury’s limb. Secondary crater chains that scour the surface and lead toward the top right of the scene appear to be from the Rembrandt basin to the north.
NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

The MESSENGER ((Mercury Surface, Space Environment, Geochemistry, and Ranging Mission) to Mercury was due to end in March 2015. Launched on August 3, 2004, it entered orbit around Mercury on March 17, 2011, for a one-year discovery mission, and has provided unprecedented views of the innermost planet.

A manoeuvre on January 21 increased the altitude of its orbit, prolonging the mission for possibly another month. Sometime in late April, the probe will descend and crash into the surface of Mercury.

Happy 25th Hubble

The Hubble Space Telescope in a picture snapped by a Servicing Mission 4 crewmember just after the Space Shuttle Atlantis captured Hubble with its robotic arm on May 13, 2009.
NASA

The Hubble Space Telescope turns 25 on April 25, 2015.

Launched into space on the Shuttle Discovery in 1990, and in spite of early problems and repairs over the years, it is still going strong. It is expected to continue through to 2018 when the James Webb Telescope is launched.

New Horizons

Artist’s concept of the New Horizons spacecraft as it approaches Pluto and its three moons in summer 2015.
Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI)

My favourite event will occur on July 14 when NASA’s New Horizons spacecraft flies by Pluto and Charon.

The probe left Earth in 2006, just after Pluto was demoted to being a dwarf planet. It will provide us with the first up close and personal images of this outer solar system object. Initial observations started in January, but the best views will occur as it flies by the dwarf planet on July 14 before heading off to visit other objects far out in the Kuiper Belt.

Rosetta

Mosaic of four images taken by Rosetta’s navigation camera on 22 January 2015 at 28.0 km from the centre of comet 67P/Churyumov-Gerasimenko.
ESA/Rosetta/NAVCAM, CC BY-SA

Rosetta successfully launched the Philae lander onto the surface of Comet 67P/Churyumov-Gerasimenko on November 2014 and continues to orbit the comet as it makes closest approach to the sun on 13 August 2015.

Rosetta’s mission is to monitor how the comet changes as it approaches the sun. It is hoped that the Philae lander, currently in hibernation, will wake up in the early months of the year as it gets more sunlight on its solar panels and again gather data.

Cassini meets Enceladus

This view looks across the region of Enceladus’ geyser basin and down on the ends of the Baghdad and Damascus fractures that face Saturn.
NASA/JPL-Caltech/Space Science Institute

In October NASA’s Cassini mission is scheduled to undertake a close flyby of Saturn’s moon Enceladus.

The flyby will allow the spacecraft to get close enough to fly through the geysers of water that have been discovered emanating from this very interesting icy moon and hopefully reveal secrets of a possible subsurface ocean.

Goodbye Voyager 2

Artist’s impression of Voyager departing our solar system and entering deep space.
NASA/JPL

2015 will also see Voyager 2 follow its younger sibling out past the edge of our solar system sometime during this year.

Both Voyager spacecraft were launched in 1977 and, with Pioneer 10, are now the most distant man-made objects in the solar system. While Pioneer 10, launched in 1972, has not been contactable since 2003, both Voyager probes continue to send information.

This is just a snapshot of some of the highlights of 2015, which is sure to be a momentous year in space exploration.

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

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The Rosetta lander detects organic matter: the seeds of life?

The Conversation

By Jonti Horner, University of Southern Queensland

Scientists working with data sent back by the now-slumbering Philae lander have announced the discovery of organic molecules on the comet 67P/Churyumov-Gerasimenko.

Finding organic compounds on 67P’s surface is not actually particularly surprising. Organic compounds have been detected in material shed by comets before, and have been observed throughout interstellar space.

But we have never before been able to measure them in-situ, and this is where Philae offers something new and exciting.

While the results are preliminary, with researchers still working on a more detailed analysis, they are a tantalising reminder of the role comets played in the origin of life on Earth.

A rough but rewarding ride

Last week, the world watched in awe as the Philae lander departed from the Rosetta spacecraft then hopped, skipped and jumped across the surface of the comet.

European Space Agency’s mission of landing on the surface of a comet – a dirty snowball left over from the solar system’s birth – is surely one of the greatest technological achievements in the history of mankind.

Unfortunately, Philae’s landing wasn’t quite as smooth as was hoped, and the lander bounced to a stop leaning against a rock, in a shadowy region of the comet’s surface.

The result – Philae currently receives too little sunlight to stay awake, and after a couple of days of frantic activity on the surface, has now gone into hibernation.

Hopefully, as the comet swings towards perihelion (its closest approach to the sun) next August, the amount of light Philae receives will increase and the lander will awake from its slumber – but we can’t know for sure.

For now, Philae’s work is done, and the baton has been passed to the teams who are now furiously studying the hard-earned data sent back to Earth before Philae fell asleep.

That data was squirted back to the Earth shortly before the lander entered sleep mode – and it is likely that exciting results will continue to appear over the next weeks and months.

The first such results have already been made public, with the scientists confirming the detection of organic molecules on the comet’s surface. Not much is currently known – the scientists are still trying to fully disentangle the story of what has been observed – but the result is a tantalising glimpse of what is to come.

Comets and the origin of life

The reason that these results are particularly exciting goes back to two of the great unanswered scientific questions:

  1. what was the origin of life?
  2. how common is it throughout the universe?

Current theories of planet formation suggest that the Earth should have formed dry – this close to the sun in the proto-planetary nebula that birthed our planet, temperatures would have been too high for water to freeze out.

As a result, Earth required hydration, and it is thought that comets such as 67P would have been one of the main sources of the Earth’s water, delivering it in countless comet collisions during the final stages of planet formation.

Beyond the question of the origin of water, though, the origin of complex chemistry, the precursor to life, has long puzzled scientists. Where did the chemical building blocks that make up life as we know it come from?

Were those compounds “cooked” in the early oceans, or in the vast tidal zones that fringed the continents following the formation of the moon?

Or did they come from beyond the Earth, delivered in the collisions that dominated the process of planet formation?

Organics from space and home

As time goes by, it is seeming ever more likely that the origin of complex organic compounds on Earth is two-fold. Some was almost certainly cooked on our planet’s surface, with the rest delivered by comets and asteroids, smashing into our planet.

It is in this context that the Philae observations are so exciting – further evidence that organic compounds are common in the universe.

Could comets hold the seeds of life?

The result is an important confirmation that such compounds must be abundant. To have detected them after just a “sniff” of the comet suggests that they’re everywhere on its surface.

And given that we know comets have crashed into the Earth in vast numbers throughout our planet’s history, we must have been repeatedly doused in the kind of compounds that are the direct precursors to life itself.

Panspermia?

Interestingly, the idea that life could have been delivered to Earth by comets has another, more speculative side – a theory known as “panspermia”. What if life didn’t start on Earth at all, but rather began elsewhere, and was delivered to our planet by rocks (or snowballs) from space?

The idea isn’t actually as far-fetched as it sounds. Experiments have shown that bacteria can survive the kind of forces that would be experienced in the collision of a comet or asteroid on a planet such as Earth.

And we know that impacts can eject solid, complete rocks from the surfaces of planets intact – we have meteorites on Earth that were definitely ejected from Mars. Still other experiments show that bacteria can survive, dormant, in the vacuum of space.

Following all of these results, it is quite possible, and perhaps even likely, that life in our solar system has been scattered back and forth between the planets over the billions of years since the planets formed. So if we do find life on Mars, then perhaps it will share a common origin with life on Earth, thanks to the countless collisions that have wracked both planets since they formed.

Some scientists go further, though, noting that life could be carried in comets from one planetary system to another. We know that they carry a rich organic budget – as demonstrated by Philae’s latest exciting result – but what if they carry more than just the precursors to life? Perhaps comets are actually an inter-stellar delivery mechanism, by which youthful planets are seeded with life as they form.

The more extreme versions of panspermia remain both speculative and controversial. Despite this, it is becoming more apparent that comets are, at the very least, a prime source of the precursors to life. They delivered the water on which life thrives, as well as the compounds upon which it is built.

Without comets, it seems, we may well not be here.

The ConversationJonti Horner does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.

This article was originally published on The Conversation. (Republished with permission). Read the original article.

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