Solving the mystery of the 'Man in the Moon': Volcanic plume, not an asteroid, likely created the moon's largest basin

The moon as observed in visible light (left), topography (center, where red is high and blue is low), and the GRAIL gravity gradients (right). The Procellarum region is a broad region of low topography covered in dark mare basalt. The gravity gradients reveal a giant rectangular pattern of structures surrounding the region. Credit: NASA/Colorado School of Mines/MIT/JPL/Goddard Space Flight Center

New data obtained by NASA's GRAIL mission reveals that the Procellarum region on the near side of the moon -- a giant basin often referred to as the "man in the moon" -- likely arose not from a massive asteroid strike, but from a large plume of magma deep within the moon's interior.

The Procellarum region is a roughly circular, volcanic terrain some 1,800 miles in diameter -- nearly as wide as the United States. One hypothesis suggested that it was formed by a massive impact, in which case it would have been the largest impact basin on the moon. Subsequent asteroid collisions overprinted the region with smaller -- although still large -- basins.

Now researchers from MIT, the Colorado School of Mines, and other institutions have created a high-resolution map of the Procellarum, and found that its border is not circular, but polygonal, composed of sharp angles that could not have been created by a massive asteroid. Instead, researchers believe that the angular outline was produced by giant tension cracks in the moon's crust as it cooled around an upwelling plume of hot material from the deep interior.

Maria Zuber, the E.A. Griswold Professor of Geophysics and also MIT's vice president for research, says that as cracks occurred, they formed a "plumbing system" in the moon's crust through which magma could meander to the surface. Magma eventually filled the region's smaller basins, creating what we see today as dark spots on the near side of the moon -- features that have inspired the popular notion of a "man in the moon."

"A lot of things in science are really complicated, but I've always loved to answer simple questions," says Zuber, who is principal investigator for the GRAIL (Gravity Recovery and Interior Laboratory) mission. "How many people have looked up at the moon and wondered what produced the pattern we see -- let me tell you, I've wanted to solve that one!"

Zuber and her colleagues publish their results this week in the journal Nature.

Making Less of an Impact

The team mapped the Procellarum region using data obtained by GRAIL -- twin probes that orbited the moon from January to December 2012. Researchers measured the distance between the probes as they chased each other around the moon. As the leading probe passed over a region of lower density, it briefly slowed, caught by that region's gravitational pull. As the probes circled the moon, they moved in accordion fashion, the distance between them stretching and contracting in response to varying gravitational attraction due to the mass variations in the lunar interior.

From the variable distance between the probes, Zuber and her team determined the strength of gravity across the moon's surface, creating a highly detailed map, which they then used to determine where the lunar crust thickens and thins.

From this mapping, the researchers observed that the rim of the Procellarum region is composed of edges that abut at 120-degree angles. As asteroid impacts tend to produce circular or elliptical craters, Zuber says the Procellarum's angular shape could not have been caused by an impact.

Instead, the team explored an alternative scenario: Some time after the moon formed and cooled, a large plume of molten material rose from the lunar interior, around where the Procellarum region is today. The steep difference in temperature between the magma plume and the surrounding crust caused the surface to contract over time, creating a pattern of fractures that provided a conduit for molten material to rise to the surface.

To test the hypothesis, the researchers modeled the region's gravitational signal if it were to contain volcanic intrusions -- magma that seeped up to just beneath the moon's surface and, over time, cooled and crystallized. The resulting simulation matched the gravity signal recorded by GRAIL, supporting the idea that the Procellarum was caused by a magma plume, and not an asteroid.

"How such a plume arose remains a mystery," Zuber says. "It could be due to radioactive decay of heat-producing elements in the deep interior. Or, conceivably, a very early large impact triggered the plume. But in the latter case, all evidence for such an impact has been completely erased. People who thought that all this volcanism was related to a gigantic impact need to go back and think some more about that."

Source: Nasa

New isotopic evidence supporting moon formation via Earth collision with planet-sized body

The moon. A new series of measurements of oxygen isotopes provides increasing evidence that the moon formed from the collision of the Earth with another large, planet-sized astronomical body, around 4.5 billion years ago. Credit: NASA/JPL

A new series of measurements of oxygen isotopes provides increasing evidence that the Moon formed from the collision of Earth with another large, planet-sized astronomical body, around 4.5 billion years ago.

This work will be published in Science on 6th June, and will be presented to the Goldschmidt geochemistry conference in California on 11th June.

Most planetary scientists believe that the Moon formed from an impact between  Earth and a planet-sized body, which has been given the name Theia. Efforts to confirm that the impact had taken place had centred on measuring the ratios between the isotopes of oxygen, titanium, silicon and others. 

These ratios are known to vary throughout the solar system, but their close similarity between Earth and Moon conflicted with theoretical models of the collision that indicated that the Moon would form mostly from Theia, and thus would be expected to be compositionally different from Earth.

Now a group of German researchers, led by Dr. Daniel Herwartz, have used more refined techniques to compare the ratios of 17O/16O in lunar samples, with those from Earth. The team initially used lunar samples which had arrived on Earth via meteorites, but as these samples had exchanged their isotopes with water from Earth, fresher samples were sought. These were provided by NASA from the Apollo 11, 12 and 16 missions; they were found to contain significantly higher levels of 17O/16O than their Earthly counterparts.

Dr Herwartz said "The differences are small and difficult to detect, but they are there. This means two things; firstly we can now be reasonably sure that the Giant collision took place. Secondly, it gives us an idea of the geochemistry of Theia. Theia seems to have been similar to what we call E-type chondrites.If this is true, we can now predict the geochemical and isotopic composition of the Moon, because the present Moon is a mixture of Theia and the early Earth. The next goal is to find out how much material of Theia is in the Moon."

Most models estimate that the Moon it is composed of around 70% to 90% material from Theia, with the remaining 10% to 30% coming from the early Earth. However, some models argue for as little as 8% Theia in the Moon. Dr Herwartz said that the new data indicate that a 50:50 mixture seems possible, but this needs to be confirmed.

The team used an advanced sample preparation technique before measuring the samples via stable isotope ratio mass spectrometry, which showed a 12 parts per million (± 3 ppm) difference in 17O/16O ratio between Earth and Moon.

Source: European Association of Geochemistry

Martian meteorite yields more evidence of the possibility of life on Mars

Is there, or was there once, life on Mars? Credit: NASA/JPL/MSSS

A tiny fragment of Martian meteorite 1.3 billion years old is helping to make the case for the possibility of life on Mars, say scientists.

The finding of a 'cell-like' structure, which investigators now know once held water, came about as a result of collaboration between scientists in the UK and Greece. Their findings are published in the latest edition of the journal Astrobiology.

While investigating the Martian meteorite, known as Nakhla, Dr Elias Chatzitheodoridis of the National Technical University of Athens found an unusual feature embedded deep within the rock. In a bid to understand what it might be, he teamed up with long-time friend and collaborator Professor Ian Lyon at the University of Manchester.

Professor Lyon, based in Manchester's School of Earth, Atmospheric and Environmental Sciences explains: "In many ways it resembled a fossilized biological cell from Earth but it was intriguing because it was undoubtedly from Mars. Our research found that it probably wasn't a cell but that it did once hold water, water that had been heated, probably as a result of an asteroid impact."

These findings are significant because they add to increasing evidence that beneath the surface, Mars does provide all the conditions for life to have formed and evolved. It also adds to a body of evidence suggesting that large asteroids hit Mars in the past and produce long-lasting hydrothermal fields that could sustain life on Mars, even in later epochs, if life ever emerged there.

As part of the research, the feature was imaged in unprecedented detail by Dr Sarah Haigh of The University of Manchester whose work usually involves high resolution imaging for next generation electronic devices ,which are made by stacking together single atomic layers of graphene and other materials with the aim of making faster, lighter and bendable mobile phones and tablets. A similar imaging approach was able to reveal the atomic layers of materials inside the meteorite.

Together their combined experimental approach has revealed new insights into the geological origins of this fascinating structure.

Professor Lyon said: "We have been able to show the setting is there to provide life. It's not too cold, it's not too harsh. Life as we know it, in the form of bacteria, for example, could be there, although we haven't found it yet. It's about piecing together the case for life on Mars -- it may have existed and in some form could exist still."

Now, the team is using these and other state-of-the-art techniques to investigate new secondary materials in this meteorite and search for possible bio signatures which provide scientific evidence of life, past or present. Professor Lyon concluded: "Before we return samples from Mars, we must examine them further, but in more delicate ways. We must carefully search for further evidence."

Source: Manchester University

Water vapor on Rosetta's target comet significantly different from that found on Earth

First measurements of comet’s water ratio. Credit: Copyright Spacecraft: ESA/ATG medialab; Comet: ESA/Rosetta/NavCam; Data: Altwegg et al. 2014

ESA's Rosetta spacecraft has found the water vapour from its target comet to be significantly different to that found on Earth. The discovery fuels the debate on the origin of our planet's oceans.

The measurements were made in the month following the spacecraft's arrival at Comet 67P/Churyumov-Gerasimenko on 6 August. It is one of the most anticipated early results of the mission, because the origin of Earth's water is still an open question.

One of the leading hypotheses on Earth's formation is that it was so hot when it formed 4.6 billion years ago that any original water content should have boiled off. But, today, two thirds of the surface is covered in water, so where did it come from?
In this scenario, it should have been delivered after our planet had cooled down, most likely from collisions with comets and asteroids. The relative contribution of each class of object to our planet's water supply is, however, still debated.

The key to determining where the water originated is in its 'flavour', in this case the proportion of deuterium -- a form of hydrogen with an additional neutron -- to normal hydrogen.

This proportion is an important indicator of the formation and early evolution of the Solar System, with theoretical simulations showing that it should change with distance from the Sun and with time in the first few million years.

One key goal is to compare the value for different kinds of object with that measured for Earth's oceans, in order to determine how much each type of object may have contributed to Earth's water.

Comets in particular are unique tools for probing the early Solar System: they harbour material left over from the protoplanetary disc out of which the planets formed, and therefore should reflect the primordial composition of their places of origin.

But thanks to the dynamics of the early Solar System, this is not a straightforward process. Long-period comets that hail from the distant Oort cloud originally formed in Uranus-Neptune region, far enough from the Sun that water ice could survive.

They were later scattered to the Solar System's far outer reaches as a result of gravitational interactions with the gas giant planets as they settled in their orbits.

Conversely, Jupiter-family comets like Rosetta's comet were thought to have formed further out, in the Kuiper Belt beyond Neptune. Occasionally these bodies are disrupted from this location and sent towards the inner Solar System, where their orbits become controlled by the gravitational influence of Jupiter.

Indeed, Rosetta's comet now travels around the Sun between the orbits of Earth and Mars at its closest and just beyond Jupiter at its furthest, with a period of about 6.5 years.

Previous measurements of the deuterium/hydrogen (D/H) ratio in other comets have shown a wide range of values. Of the 11 comets for which measurements have been made, it is only the Jupiter-family Comet 103P/Hartley 2 that was found to match the composition of Earth's water, in observations made by ESA's Herschel mission in 2011.

By contrast, meteorites originally hailing from asteroids in the Asteroid Belt also match the composition of Earth's water. Thus, despite the fact that asteroids have a much lower overall water content, impacts by a large number of them could still have resulted in Earth's oceans.

It is against this backdrop that Rosetta's investigations are important. Interestingly, the D/H ratio measured by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis, or ROSINA, is more than three times greater than for Earth's oceans and for its Jupiter-family companion, Comet Hartley 2. Indeed, it is even higher than measured for any Oort cloud comet as well.

"This surprising finding could indicate a diverse origin for the Jupiter-family comets -- perhaps they formed over a wider range of distances in the young Solar System than we previously thought," says Kathrin Altwegg, principal investigator for ROSINA and lead author of the paper reporting the results in the journal Science this week.

"Our finding also rules out the idea that Jupiter-family comets contain solely Earth ocean-like water, and adds weight to models that place more emphasis on asteroids as the main delivery mechanism for Earth's oceans."

"We knew that Rosetta's in situ analysis of this comet was always going to throw up surprises for the bigger picture of Solar System science, and this outstanding observation certainly adds fuel to the debate about the origin of Earth's water," says Matt Taylor, ESA's Rosetta project scientist.

"As Rosetta continues to follow the comet on its orbit around the Sun throughout next year, we'll be keeping a close watch on how it evolves and behaves, which will give us unique insight into the mysterious world of comets and their contribution to our understanding of the evolution of the Solar System."

Source: ESA

Asteroids made easy: 'Patch of asteroid' being built inside a satellite

ASU researchers build their own "patch of asteroid" inside of a small spinning satellite seen here in this artist rendering. Credit: Sean Amidan

A dozen astronauts have walked on the moon, and several rovers have been piloted on Mars, giving us a good understanding of these off-world environments. But when it comes to asteroids, scientists enter uncharted territory.

Landing on an asteroid is notoriously difficult.

Asteroids have very little gravity because they have very little mass. Most of them appear to be rubble piles held together loosely, with surfaces covered in boulders and gravels and fine materials, much like the moon, but with a lot more cohesion. On an asteroid, a rock the size of a bank building weighs as much as a cricket on Earth, making an astronaut like a superman. But what would you anchor to, what you would land on and how would you move around?

Because scientists and engineers don't know the most basic mechanical properties of an asteroid, sending a billion dollar landing mission to an asteroid is risky, and even likely to fail, until some preliminary investigations are conducted, requiring years of lead time.

A team at Arizona State University is looking to mitigate that risk and improve that schedule by building its own "patch of asteroid" inside of a small, spinning satellite costing less than $100,000. The project is called the Asteroid Origins Satellite, or AOSAT I.

"Landing on asteroids is one of the biggest challenges of our time," roboticist Jekan Thanga said.

Thanga, an assistant professor in the School of Earth and Space Exploration at ASU, is the engineering principal investigator for AOSAT I. "And space agencies worldwide, including NASA, are very focused on meeting that challenge."

Erik Asphaug, a planetary scientist and professor at ASU, is the science principal investigator for AOSAT I. He and Thanga plan on launching a miniature satellite later this year that will serve as the world's first CubeSat microgravity laboratory. A CubeSat is a modular small satellite with a 10-by-10 centimeter base and various unit lengths. AOSAT I will be a 3U configuration, about the size of a loaf of bread, with two spun-up laboratories in the outer units, each housing a patch of real asteroid surface material.

In the first flight, one chamber will be filled to a depth of a few centimeters with very fine material representative of interstellar dust, or the fine "ponds" seen on several asteroids. 

The second chamber, otherwise identical, will be filled with bits of shock-fragmented chondrite meteorite material. Once launched into space and freely orbiting, these rocks will just tumble around -- itself an interesting experiment. But to build a realistic regolith surface for scientists to explore, the satellite is spun, to create microgravity-like conditions.

"We're taking asteroid material that landed on Earth and sending it back into space," Asphaug said. "It's a low-cost laboratory that really physically builds a patch of asteroid. It'll be asteroid gravity. It'll be made of asteroid stuff. We can do all sorts of experiments."

To simulate the gravity field of a 300-meter-diameter asteroid, AOSAT I spins once every 4.5 minutes. It can spin faster to reproduce the regolith (surface material) conditions for much larger asteroids. This spin configuration is easily attained and stabilized by off-the-shelf approaches, making it a great approach for students to learn on.

While much of the CubeSat is off-the-shelf, the approach is novel. CubeSats have typically been used to test engineering designs in space, since it is a really constrained and relatively new form factor. Great science has been performed on CubeSats, although this has only been observational so far. CubeSats have not yet been used to do "test tube and beaker-type" experiments of the sort that are planned for AOSAT I, Thanga said.

Experiments will be conducted robotically in the end chambers. When AOSAT I is not spinning, it is a zero-gravity capsule. Here, experiments will be done to understand how dust clumps together to form asteroids -- a process that plays out in zero gravity over long timescales. A simple robotic plunger is being designed to interact with the patch of regolith, and can be used to accrete a globule of particles, a miniature rubble pile asteroid that can be spun and shaken, observed by stereo cameras.

When AOSAT I starts to spin, these piles of grains will get accelerated to the outer walls. Observing that process will tell us much about nebular grain behavior and microgravity particle flows on asteroids, for example, following the formation of a crater.

Once the spinning AOSAT I has stabilized (once per few minutes), experiments will be conducted to give a better understanding of what asteroid surfaces are like. "The questions are very basic, and that's what makes this so much fun," says Asphaug. When you push slowly on a rock, does it lock into place or does it push aside the other rocks and slide into the surface? Do patterns form when you send a vibration through the regolith? Does cohesion dominate overwhelmingly over gravity, so that rocks stick together into aggregates? What happens when you charge the particles?

Asphaug and Thanga hope to answer these questions to help determine what kinds of devices would be best for landing on real asteroids. "An asteroid could just be lots of rock, just grouped together into this larger entity, but there's nothing holding it together," Thanga said. "So if something is going to grapple and try to land on this, there's nothing to grapple to."

Despite the small scale of the experiments (the asteroid patch will be slightly smaller than a CD case), Asphaug and Thanga are confident in the real-world applications of AOSAT.

"These rocks might not be able to tell the difference, whether they are in the AOSAT centrifuge or back on their home asteroid," says Asphaug. Once the AOSAT is spun up to mimic the gravity field of a ~300 m asteroid (gravity field 10-5 that of Earth), then it can be used to test mechanisms for asteroid landing. The first AOSAT will use a simple arm that does some basic interactions, while next generation AOSATs will be configured with more advanced robotic equipment.

Thanga uses the analogy of a wind tunnel to describe the scientific approach to their experiments. In a wind tunnel, researchers subject small-scale models of aircraft to conditions they expect in flight. The calculations and designs are then scaled up and applied to the real thing. "We can test asteroids in this wind tunnel-like analogous system, prove and disprove theories, and get a better understanding of our models," says Thanga.

Landing on an asteroid may be extremely difficult, but it's also an extremely desirable goal, from many points of view. Mining asteroids, colonizing asteroids or using asteroids as stepping stones to Mars and the other planets used to be the stuff of science fiction. Now it is on the desk of NASA administrators, who are being asked to find ways to divert hazardous asteroids, and to discover new ways to utilize asteroids, and to involve asteroids as part of the astronaut pathway to Mars.

Viranga Perera, a graduate student at ASU who is managing the project systems engineering, thinks it is "fascinating that this very low-cost AOSAT platform can be used to study such a fundamental concept as planetary accretion, and that it can serve as a test bed for future asteroid sample return missions."

The School of Earth and Space Exploration is an academic unit in ASU's College of Liberal Arts and Sciences.

Source:  Arizona State University College of Liberal Arts and Sciences