Category Archives: Moons

New NASA study shows Moon once had an atmosphere


A new study shows that an atmosphere was produced around the ancient Moon, 3 to 4 billion years ago, when intense volcanic eruptions spewed gases above the surface faster than they could escape to space. The study, supported by NASA’s Solar System Exploration Research Virtual Institute, was published in Earth and Planetary Science Letters.

When one looks up at the Moon, dark surfaces of volcanic basalt can be easily seen to fill large impact basins. Those seas of basalt, known as maria, erupted while the interior of the Moon was still hot and generating magmatic plumes that sometimes breached the lunar surface and flowed for hundreds of kilometers. Analyses of Apollo samples indicate those magmas carried gas components, such as carbon monoxide, the ingredients for water, sulfur, and other volatile species.

In new work, Dr. Debra H. Needham, Research Scientist of NASA Marshall Space Flight Center, and Dr. David A. Kring, Universities Space Research Association (USRA) Senior Staff Scientist, at the Lunar and Planetary Institute (LPI), calculated the amounts of gases that rose from the erupting lavas as they flowed over the surface and showed that those gases accumulated around the Moon to form a transient atmosphere. The atmosphere was thickest during the peak in volcanic activity about 3.5 billion years ago and, when created, would have persisted for about 70 million years before being lost to space.

The two largest pulses of gases were produced when lava seas filled the Serenitatis and Imbrium basins about 3.8 and 3.5 billion years ago, respectively. The margins of those lava seas were explored by astronauts of the Apollo 15 and 17 missions, who collected samples that not only provided the ages of the eruptions, but also contained evidence of the gases produced from the erupting lunar lavas.

NASA’s Needham says, “The total amount of H2O released during the emplacement of the mare basalts is nearly twice the volume of water in Lake Tahoe. Although much of this vapor would have been lost to space, a significant fraction may have made its way to the lunar poles. This means some of the lunar polar volatiles we see at the lunar poles may have originated inside the Moon.”

David Kring notes, “This work dramatically changes our view of the Moon from an airless rocky body to one that used to be surrounded by an atmosphere more prevalent than that surrounding Mars today.” When the Moon had that atmosphere, it was nearly 3 times closer to Earth than it is today and would have appeared nearly 3 times larger in the sky.

This new picture of the Moon has important implications for future exploration. The analysis of Needham and Kring quantifies a source of volatiles that may have been trapped from the atmosphere into cold, permanently shadowed regions near the lunar poles and, thus, may provide a source of ice suitable for a sustained lunar exploration program. Volatiles trapped in icy deposits could provide air and fuel for astronauts conducting lunar surface operations and, potentially, for missions beyond the Moon.

Over the past decade, the search for volatiles within the Moon and on the surface of the Moon has intensified. Those volatiles may hold clues about the material that accreted to form the Earth and Moon and, thus, our planetary origins. The volatiles may also provide the in-situ resources needed for sustained lunar surface activities that may follow the development of NASA’s new Orion crew vehicle and a Gateway structure that may orbit the Moon. In addition, robotic assets, like NASA’s Resource Prospector, are being developed to explore the nature and distribution of volatile deposits that might be suitable for scientific analysis and recovery. Based on the new results of Needham and Kring, those assets may be recovering ice that is partially composed of volatiles erupted from volcanic fissures over 3 billion years ago.

The new research was initiated from the LPI-Johnson Space Center’s (JSC) Center for Lunar Science and Exploration, led by Kring and supported by NASA’s Solar System Exploration Research Virtual Institute. Needham is a former postdoctoral researcher at the LPI. The LPI is operated for NASA by Universities Space Research Association (USRA).

NASA: Saturn moon Enceladus is able to host life – it’s time for a new mission


David Rothery, The Open University

Ever since studies started suggesting that chemical reactions between water and rock on Saturn’s moon Enceladus could provide enough energy in the water to feed microbial life, scientists have been searching for proof that the right sort of reactions really do occur. The Conversation

And during its last dive through the icy plumes that Enceladus erupts into space in October 2015, the Cassini spacecraft has finally managed to find it – in the form of molecular hydrogen. The finding, published in Science, means the moon can now be considered highly likely to be suitable to host microbial life. In fact, the results should undermine the last strong objection from those who argue it could not.

Enceladus is a small (502km in diameter) moon with an icy surface, a rocky interior and an ocean of liquid water sandwiched between the two. Cassini discovered back in 2005 that Enceladus is venting water into space, in the form of plumes of ice crystals escaping from cracks in the surface. For a decade, Enceladus was the only icy moon where this was known to happen, but plumes have recently been found on Europa, too, a larger icy moon of Jupiter.

Cassini’s discovery led to it being re-tasked to fly through Enceladus’s plumes. There, in addition to water, it was able to identify traces of methane, ammonia, carbon monoxide, carbon dioxide, simple organic molecules and salts.

Cutaway view inside Enceladus, showing where hot water and rock interact below the ice.
NASA/JPL

Eventually, in March 2015, it detected microscopic particles of silica. By then, the composition of the plumes showed almost every sign that ocean water had reacted chemically with heated rock – altering the minerals of the rocky silicate seabed while the water became rich in chemicals.

Presumably, the ocean water is drawn into the rock, becomes heated, reacts chemically, and escapes back up to the ocean via “hydrothermal vents”. These exist on the floor of the Earth’s oceans, too, where the chemically charged water supports a rich ecology of microbes and other, more complex, life forms – requiring no sunlight.

The only missing evidence of water-rock chemical reactions in Enceladus was molecules of hydrogen, which should be released as a byproduct of the water-rock reactions. Searching for hydrogen was a key goal of Cassini’s final and closest dive through the plumes.

The new study unveils how hydrogen was detected during the frantic half-minute when Cassini was about 120km above the surface of Enceladus, whizzing through a plume at 8.5km per second. This was achieved by operating the mass spectrometer (an instrument which knocks electrons off chemical substances and sorts them based on their mass-to-charge ratio) in a special mode. It admitted plume material directly into the instrument’s detection chamber to avoid the possibility of hydrogen being generated by plume-water reacting with the metallic components of the instrument itself.

The astrobiology

Hydrogen is of immense significance, because its presence along with hot water and rock would enable simple microbes to make a living. When dissolved carbon dioxide reacts with dissolved hydrogen, it produces methane and water. This chemical reaction releases energy that organisms can use to drive their metabolism. There are many kinds of “methanogenic” organisms at deep sea hydrothermal vents on Earth that do this. Now that we know Enceladus has all the necessary ingredients for this to happen, we are lacking only the proof of life itself.

For that we will need a purpose-built mission, such as the Enceladus Life Finder (ELF). This would collect and analyse any complex organic molecules in the plumes. It is hard to imagine a more important goal for solar system exploration than establishing whether a habitable environment, such as the warm bottom of Enceladus’s ocean, actually does host life.

Enceladus’s south polar plumes, as seen by Cassini November 30 2010.
NASA/JPL-Caltech/Space Science Institute

Enceladus is a long way from Earth. If we were able to prove that it hosts life, it would be highly likely that such life had originated there, independently of life on Earth. That would be a crucial discovery. It would provide evidence to suggest that our galaxy is teeming with life, because if life began independently on two different bodies in our solar system, then surely it also got going on many of the potentially habitable planets that we are now finding around other stars.

Enceladus is a tiny world, and the amount of available energy and nutrients is small. Few scientists therefore expect it to host an ecosystem consisting of more than simple microbes. The much larger Europa, if it has life too, is a better prospect.

How Cassini will end, on September 15, 2017.
NASA/Jet Propulsion Laboratory-Caltech

However, to protect Enceladus from the slightest risk of contamination by any terrestrial microbes that accidentally hitched a ride on Cassini, the craft will not be allowed to become a derelict object that might eventually crash onto its surface. Instead, the mission is facing its “grand finale”, a series of 22 orbits in which it will pass spectacularly between Saturn and its innermost ring. This will end with Cassini burning up in Saturn’s atmosphere.

David Rothery, Professor of Planetary Geosciences, The Open University

This article was originally published on The Conversation. Read the original article.

Fly me to the Moon? Why the world should be wary of Elon Musk’s space race


Alan Marshall, Mahidol University

Want to fly to the moon? Well, now you won’t have to bother with all those years of rigorous astronaut training – all you need is a huge wad of cash. Elon Musk, technopreneur, has built a small spaceship called Dragon and if you slap down enough money – maybe a hundred million dollars or so – he’ll fly you to the Moon. The Conversation

The first flight is set for 2018, a target so ambitious it verges on the incredible.

Musk’s moonshot plan has been greeted enthusiastically by most space fans but some are a little doubtful. Other commentators remain totally uninspired, ridiculing the idea as a gigantic waste of money.

This ambivalence isn’t surprising really, since history shows that soon after the Apollo 11 moon landing in 1969, people switched their televisions to more down-to-earth events while wondering why NASA kept going back to the Moon again and again with Apollo 12, then Apollo 13, then Apollo 14 – all the way up to Apollo 17.

Natural process, or a social one?

Musk would tell you he’s not using taxpayer funds for his moonshot and that his SpaceX venture is a private commercial business. But SpaceX’s only significant customer so far has been NASA – a taxpayer-funded agency that pays it to deliver cargo to the International Space Station.

And even before SpaceX had delivered anything, NASA made a massive investment in the firm to get it up and running. Any claim that SpaceX is purely a commercial business, then, is also incredible.

Like many space fans, Musk will tell you that this moonshot is the first step in the “natural process” of human space expansion. The next steps involve the colonisation of the Moon and then Mars.

But space travel is not a natural process; it’s a social process involving domestic politics, international competition, the marketing of patriotic heroism, and the divvying up of state funds.

Harkening back to the dark past

The “colonisation” theme of space expansion is also problematic since it signifies a potential re-emergence of the social injustices and environmental disasters wrought by past colonial ventures. Being a fan of “space colonisation”, then, can be likened to rejoicing in the displacement of native peoples and celebrating the destruction of wilderness.

Unfortunately, too often space expansion has utilised historic conquests to map out the future; witness Star Trek’s Space: the Final Frontier theme, or Musk’s own idea to colonise Mars.

Calling for a new “age of exploration” in space recalls past voyages of discovery ignores how Chritopher Columbus decimated native tribes with smallpox and how Spanish conquistadors ransacked Meso-America’s temples to loot gold.

Space fans might argue that there are no people in space to be colonised, that the Moon and Mars are uninhabited lands. But the plan to settle Mars, for example, and then to set about extracting valuable resources without working out if some alien species is living there – even if those life forms are microbial – seems reckless.

It also smacks of anthropocentrism since humans will doubtless carry to Mars the attitude that microbes are lower lifeforms and that it’s OK to stomp all over their planet spreading pollution and mucking up their environment.

Even if they are lifeless, we should consider that the Moon and Mars belong to all of us; they are the common heritage of humankind. And those who first to get to the Moon or to Mars shouldn’t be permitted to plunder these worlds just for the sake of their own adventure or profit.

An alliance of interests

One prominent fan of American space expansion is US President Donald Trump. “Space is terrific,” he said in Florida last year. Trump also called for more space exploration in his recent speech to Congress.

Many scientists are wary of Trump’s attitude to science but, in a surprising willingness to embrace both science and the wider universe beyond America, the president wants NASA to “explore the mysteries of deep space”.

In the process, Trump is also working out how to rid NASA of the those pesky climate scientists who, he claims, are peddling “politicised” science.

Trump met Elon Musk within days of assuming the presidency and, with their shared love of capitalism and penchant for self-promotion, they seem to be entering a working relationship, described by some as cronyism.

Trump seems willing to support Musk if the entrepreneur can help Make America Great Again by shooting Americans off to the Moon before China gets there. Musk may seem confident about his 2018 plans because he believes he has presidential blessing.

A note of caution

But perhaps it’s too soon to worry about Moon grabs or Martian colonialism.

First, both Trump and Musk are notorious “big talkers” and they may be playing with the macho spectacle of space travel. If their space plans gurgle into an economic sinkhole, they’ll probably quietly abandon them.

And the 2018 moonshot is not going to actually land on the Moon; it’s merely going to shoot around it and then head back to Earth. Nobody will get the chance to plant a flag.

Space tourism, moon bases and Martian colonies have all been predicted for decades and nothing has ever come of them. Wernher von Braun, the Apollo rocket hero (and ex-Nazi) showcased such prospective space endeavours on a television show with Walt Disney in the 1950s (using whizzing Disney graphics). But 70 years later, a space colony is nowhere to be found.

An outright Moon grab would also be illegal, since the 1967 UN Outer Space Treaty forbids such acts. The US has re-interpreted this treaty to suggest that it permits resource extraction from the Moon and the planets in the Solar System, but not all nations accept this view.

Not what we all want

If Musk does get his rich clients to circle the Moon next year, and then manages to set up bases and colonies on the lunar surface and then Mars, it won’t be because he’s made a business success out of space expansion. And it won’t be due to the scientific merit of moon bases.

Rather, it will be because he has managed to dupe the American taxpayer with expensive technological fantasies and because he’s broken the ideal of the common heritage of mankind enshrined in international law. Humanity and the Earth will be diminished in the process.

It’s possible the cosmos will be diminished and despoiled too with mining firms digging up the moonscape, rocket fuel spilled all over the Martian surface, and neon lights flashing in shiny space casinos.

Of course, some space fans believe the only way they’ll realise their space fantasies is to ride behind the glory of “visionaries” such as Musk – and the unknown mega-rich space passengers set to shoot off around the Moon next year.

But the Earth abounds with those willing to poke fun at such showy space adventures, which is good – Musk needs to know that not everybody is on board.

Alan Marshall, Lecturer in Environmental Social Sciences, Faculty of Social Sciences and Humanities, Mahidol University

This article was originally published on The Conversation. Read the original article.

The search of life beneath the ice: why we’re going back to Europa


Last month NASA gave the “all systems go” for a new mission to Europa. But why go back? After all, we’re still sifting through the data from the Galileo probes fly-bys from more than a decade ago.

The short answer: it’s all about life.

The Jovian moons – named after Jupiter’s lovers by Simon Marius – have been a source of scientific speculation since Galileo trained his telescope on Jupiter in 1610, announcing his discovery in the Sidereal Messenger.

But the idea that Europa and other moons of Jupiter might harbour life is relatively new, as is the notion they might have hidden oceans beneath their icy surfaces. Indeed, these speculations demonstrate just how fast our conceptions of the solar system, and life, can change.

Speculative science, speculative fiction

A generation of space scientists and enthusiasts who grew up on Robert A. Heinlein’s “juveniles” will fondly remember Farmer in the Sky, written in 1950, when the Jovian moons were believed to be rocky, like our own Moon.

But in the late 1950s and continuing through the early 1970s, a growing body of telescopic data suggested that some of these moons, in particular Callisto, Ganymede and Europa, were covered in water ice. This speculation came from their high albedo, a measure of how much they light they reflect. With an albedo of 0.64, Europa is one of the most reflective bodies in the solar system.

In 1971, Carl Sagan suggested that the Jovian moons, including Europa, were of “major…exobiological significance”. In other words: they might harbour life.

Europa as seen by Voyager 2 during its close encounter in 1979.
NASA/JPL

The early 1970s also saw the first speculation that some outer moons of the solar system, including Europa, might hide an ocean beneath their surfaces. It was initially suggested this might be due to radiative heating, although it was later proposed that the heat might come from tidal forces induced by Jupiter, especially because of the synchronous orbits of the three innermost Galilean moons: Io, Europa and Ganymede.

The 1979 Voyager fly-bys confirmed that Callisto, Europa and Ganymede moons were covered in ice and that Io was extremely volcanic. The best images of Europa were taken by Voyager 2 from a range of 204,400 kilometres, showing Europa to be “billiard ball” smooth.

Not too hot, not too cold…

Things took a turn following the discovery by Robert Ballard’s 1977 expedition of entire ecosystems thriving near hydrothermal vents in the deep ocean. These vents existed in the “midnight zone”, without sunlight and photosynthesis, and changed the way we thought about life.

The discovery of life around deep ocean vents, like this one, raised the exciting prospect of life existing under the ocean on Europa.
P. Rona/NOAA

In 1980, scientists Gerald Feinberg and Robert Shapiro hypothesised that deep sea volcanism might support life on the Jovian moons. The Feinberg-Shapiro hypothesis is one of the major reasons for the current interest in Europa by astrobiologists.

In essence, it was proposed there might be a tidally heated habitable zone around giant planets, similar to the habitable, or “Goldilocks” zone around a star: where it’s not to hot, not to cold, and where liquid water and life can exist.

The idea of life on the Jovian moons was quickly picked up by science fiction writers. In Arthur C. Clarke’s 2010: Odyssey two (1982) and 2061: Odyssey three (1988), aliens transform Jupiter into a star kick-starting the evolution of life on Europa, transforming it into a tropical ocean world forbidden to humans.

In Bruce Sterling’s 1985 Nebula Award nominee, Schismatrix, Europa’s ocean is colonised by a group of genetically transformed post-human species.

Fire and ice

Europa and life were thus well and truly established in the minds of science fiction writers, planetary scientists, exobiologists and the public by the time NASA’s extraordinary Galileo mission began taking images of Europa in 1996.

This is the colour view of Europa from Galileo, taken in the 1990s, that shows the largest portion of the moon’s surface at the highest resolution.
NASA/JPL

By the completion of its primary mission on December 7 1997, Galileo had made eleven encounters with Europa. Galileo’s extended mission became one of “fire and ice”: its twin foci were Io’s vulcanism and Europa’s icy oceans. The Europa fly-bys took the probe to within a few hundred kilometres of the moon’s surface.

These extensive observations of Europa by the Galileo mission were compelling evidence for a liquid water ocean some 100 to 200 kilometres thick on which “floats” an outer shell of ice. Magnetometer measurements indicate the ocean is free flowing and salty.

Galileo also provided spectacular views of the icy terrain: ridges, slip faults and “ice-bergs”, all adding to the picture of a surface only 10-100 million years old, which is young by the four to five billion year age of the solar system.

The spacecraft, nearly out of fuel after an extended mission, was deliberately crashed into Jupiter on 21 September 2003 to protect Europa from possible contamination.

Europa Report

The data Galileo collected are still revealing new important finds. There evidence of clay-like minerals on the surface, possibly from asteroid or meteorite collision, and signs of sea salt, discoloured by radiation, making up some of the dark patches observed by both Voyager and Galileo.

A whole new generation of scientists is eagerly awaiting the data from the new mission. Astrobiology has become, since the early 2000s, a whole new science discipline. This “alien ocean” mission is clumsily named, at present, Europa Multiple Flyby Mission.

So the new mission, slated for a rendezvous with Europa in 2030, won’t involve a lander. And until we can send a probe into the icy depths of Europa’s sea, speculation about what might be lurking there, à la Sebastián Cordero’s Europa Report, will remain the domain of science fiction and scientists’ fantasy. Maybe one day, it will be science fact. Europa, here we come.

The Conversation

Morgan Saletta is Doctoral Candidate History and Philosophy of Science at University of Melbourne.
Kevin Orrman-Rossiter is Graduate Student, History & Philosophy of Science at University of Melbourne.

This article was originally published on The Conversation.
Read the original article.

Huge dust cloud discovered around the Moon – but ‘lunar glow’ remains a mystery


Astronauts on the early Apollo missions orbiting over to the dark side of the moon were surprised to discover a mysterious, bright crescent of light glowing at the horizon. The controversial explanation was sunlight scattered by dust high in the Moon’s tenuous atmosphere, but proof has been hard to come by. Fast forward half a century and, for the first time, a team of scientists has analysed the Moon’s atmospheric dust in real time, discovering a permanent dust cloud. Surprisingly, however, they have failed to explain the glow.

At 384,400 km away, the Moon is our nearest planetary neighbour. It is the only celestial body that humans have set foot on and has it provided a natural tool for understanding the origin of water on Earth, the physics of our Sun and for testing fundamental theories of physics. It has even been discussed as a possible alternative home for humanity.

Despite its proximity, there’s a lot we don’t know about the Moon – in particular about its atmosphere. The glow was first spotted in 1966 and 1968 by cameras onboard NASA’s Surveyer landers – the robotic precursors to manned Apollo landings. It has later been seen by astronauts on some Apollo missions, but not all.

The white area on the edge of the moon is the glow, and the bright dot at the top is the planet Venus.
NASA

The team of scientists trying to understand the dust environment of the Moon, including the lunar glow, discovered a permanent, elongated cloud of dust around the Moon at heights between 10 to 260 km above the lunar surface using NASA’s Lunar Astmosphere and Dust Environment Explorer (LADEE) spacecraft. The authors argue that this cloud is caused by high-speed bombardment by dust particles from comets.

Interplanetary dust particles are thought to hit the surfaces of airless bodies in the solar system, generating charged and neutral gas clouds, as well as secondary dust particles that are ejected from the surface of the body on impact.

Clouds of dust particles, bound by gravitational forces, have been found around the icy moons of Jupiter and Saturn. But until now, none had been identified around rocky bodies with dusty surfaces such as the Earth, Moon and Mars.

Has lunar glow explanation turned to dust?

The gravitational pull of the Moon is approximately one-sixth of that of Earth, which is thought to be too weak to maintain a permanent and substantial atmosphere. Instead, the Moon has a tenuous layer of neutral gas called an exosphere. Debate over the presence of dust in that exosphere has raged ever since sightings of the lunar horizon glow during the Apollo era.

Ladee looking for answers
NASA

The team behind the study used an instrument called the Lunar Dust Experiment (LDEX) designed to study the physical characteristics and origin of lunar dust over a period of time, including during meteoroid showers. It was developed to search for a high-density dust cloud that could account for the glow seen by the Apollo astronauts. With superior sensitivity and closer approach to the Moon than previous missions, LDEX recorded 140,000 dust hits at various altitudes from the lunar surface and for a range of dust particle sizes.

The team estimated the average total mass of the dust cloud to be 120kg. However, unlike the dust atmosphere’s of Jupiter’s moons, the lunar dust cloud is not evenly distributed or spherically symmetric. Instead, the authors found that the cloud is elongated in a way that matches the properties of the incoming interplanetary dust bombardment and indicates that comets are the dominant source of this dust rather than slower dust particles from asteroids.

The LADEE mission ended with its planned impact into the far side of the Moon in April 2014 at a speedy 3,600 miles per hour, destroying and probably vapourising it on impact.

Mysteries remain

For the origin of the glow seen on Apollo missions’, the team failed to find evidence of the relatively dense cloud of tiny dust particles lofted into the exosphere that would explain Apollo observations. In fact, the cloud the study recorded was 100 times less dense than the Apollo missions had predicted. Although disappointing for those seeking an explanation, this may be more positive for future human exploration missions or aspirations to use the Moon as a base for conducting sensitive astronomical observations, which require a clear view of the sky.

The result means that unless we want to dismiss the observations by the Apollo missions, we may need to re-assess our understanding of the conditions of the lunar surface and perhaps even the solar wind and resulting radiation field that was predicted to charge the dust and lift it into the atmosphere.

The Conversation

Carole Mundell is Head of Astrophysics at University of Bath.

This article was originally published on The Conversation.
Read the original article.

How the Moon Was Formed


The moon is the result of a primordial collision between a Mars-sized planetary body and our planet, but little else beyond this is certain about the silvery world we can see whenever we look at the sky. Despite 61 space missions, six of which were landings, where astronauts collected moon rock samples, there are a whole host of questions. Particularly – exactly how much of the moon, a natural satellite is actually made up from Earth, and how much from this strange, lost world – and what was it like?

Researchers working in France and Israel might have enough evidence to answer one of those questions, finding more about the smaller planetary body that hit us. Apparently, it’s not all that different from home – with a composition that was likely similar to Earth. The latest models proposed suggest that the moon’s current composition is explained best if whatever happened to strike the Earth also formed nearby, in the early days of our solar system – a time of extreme chaos. It is believed that Jupiter alone caused a number of violent collisions between the other worlds in our solar system, before being dragged to its current orbit by Saturn. Two subsequent studies have proposed that both of these worlds continued to accumulate new material as they were continually bombarded with smaller protoplanets. Unlike the moon, however, Earth managed to gather more of this cosmic dust.

The most supported explanation is the “giant impact hypothesis,” which states that the moon first came into being about 4.5 billion years ago, the remains of an accident in which our planet was struck by an object approximately the size of a planet, roughly one tenth the mass of Earth. Attempted recreations of what happened and recent studies of the moon rock samples have suggested that our moon should consist primarily of remains from this mysterious impactor, which planetary scientists call Theia. If this is the case, it would explain why so many of the moon rocks resemble the minerals composing the Earth’s mantle.

The main problem faced by the researchers is that so often, planets bear very distinct compositions from each other. Mars, Mercury and the big asteroids like Vesta, for all that they have in common, also have slightly differing ratios of their respective elements. If this world known as Theia first developed in a remote part of the solar system, then its makeup would be significantly different from that on Earth, and therefore the bulk of the moon should not be so similar to the Earth’s mantle. It had to have struck Earth with a glancing blow, anything stronger could have destroyed it well before the first life forms began appearing on its surface.

In their effort to solve the problem, Alessandra Mastrobuono-Battisti and Hagai Perets at the Israel Institute of Technology both pored over data from a series of simulations – covering the scenarios of 40 different artificial solar systems. The effort applied more computer power than had been utilized by any previous study. The model simulated the growth of the planetary bodies we’re familiar with and then set them off in a game of cosmic billiards, consistently striking each other with their orbits.

When they developed this new simulation, they considered that any planets found farther away from our sun typically contain a greater relative abundance of oxygen isotopes, consistent with chemical mixes observed within the Earth, as well as the moon and Mars. Therefore any such planetesimals that were to form near our planet would contain similar chemical traces. “If they are living in the same neighborhood, they will be made of roughly the same material,” said Perets.

The team described their work in the journal Nature: the majority of these interplanetary collisions were about 20 to 40 percent—big, occurring among bodies that had formed from similar distances near the sun, which was responsible for their similarities in makeup. It’s far less likely that Theia would have sailed a long distance before impacting the planet, and the study lends credence to this idea.

Not all is readily explained in their work. There’s still a wealth of the element tungsten, which needs to be explained. This element, categorized as a siderophile – iron-loving, is expected to sink towards planetary cores as time progresses, something that would affect its variability on planets throughout the solar system, even if they did in fact form at the same time, as Earth and Mars are believed to. Bodies develop their That’s because bodies of cores with different rates, based on a number of variables including size. Although a little mixing as a result of the impact is inevitable, much of Theia’s tungsten-rich mantle material would be flung into orbit from the explosion and eventually incorporated into the moon, making the amounts of tungsten on Earth and the moon considerably different.

In the two independent studies which appeared separately in the journal Nature, Thomas Kruijer at the University of Münster in Germany and Mathieu Touboul at the University of Lyon in France compared the ratio from two tungsten isotopes— both tungsten-184 and tungsten-182 – found in both moon rocks as well as within the Earth’s mantle. According to the teams, these moon rocks contain slightly more tungsten-182 than has been found on Earth.

This is quite an exciting find, especially since this particular isotope of tungsten is actually the result of radioactive decay from an isotope derived of the element hafnium. Its half-life is rather short, approximately nine million years. Because the iron-loving tungsten has a tendency for sinking towards a planet’s core, the hafnium isotope remains closer to the surface, where over an extended period of time, it transforms into tungsten-182. That means there’s an excess of tungsten-182 within a planet’s mantle contrasted with tungsten-184 and other naturally occurring isotopes.

The difference of this isotope on both the Earth and the moon is comparatively small: the two studies rate this level at somewhere between 20 to 27 parts per million. Even a shift this minimal would mean a great deal of chemical fine-tuning, said Kruijer, meaning that chance occurrences are a bit unlikely. “Varying the tungsten by only a percent or so has a dramatic effect,” he says. “The only solution is if the mantle of proto-Earth had similar tungsten-182 content to Theia, and the core of the impactor directly merged with Earth’s.”

That’s not so likely, however. Although most of Theia’s core, considerably heavier than the mantle, shall remain a part of planet Earth, the mantle itself will continue to mix with that of the Earth as it continues to be flung through orbit. As the moon gradually accretes, more chemical mixing will take place. Although the ratio of Theia’s core and its mantle material that actually transforms into parts of the moon is left up to random chance, there must have been at least a small degree of core material, according to Kruijer. Touboul’s team arrived at a similar conclusion: Were these differences in the tungsten actually the result of a random mixture when Theia’s shards sloshed across the Earth, our moon would be a great deal different than it presently is.

Therefore, the simplest and most plausible solution, according to the authors of the study, is known as the “late veneer” hypothesis, positing that the Earth along with the proto-moon began with tungsten isotope ratios that were similar to each other. Since Earth was a much larger and more massive body, it would continuously draw in more planetesimals following the impact, giving the mantle new material to build a crust. The veneer from those planetary fragments would then have significantly more tungsten-184 compared to tungsten-182, and the moon would then contain the same ratio due to the impact.

“This looks like solid data,” Fréderic Moynier, a cosmochemist and astrophysicist at the Institut de Physique du Globe de Paris, said in an email. “It fits with the present theory of late veneer, which is simply based on the elemental abundance of the siderophile elements (such as tungsten): there are simply too many siderophile elements in the present Earth’s mantle (they should all be in the core) and therefore they must have been brought to Earth after core formation via meteorite impacts.”

There is one remaining mystery to be solved. For the moon to remain identical to the Earth’s tungsten ratio, Theia and Earth would have had to begin with similar degrees of tungsten in their composition. Where did it all go? While there are a number of questions to arise from the study, ones that future studies hope to answer in the near future, it seems like a bit more light is waxing over the story of the moon’s origins.

James Sullivan
James Sullivan is the assistant editor of Brain World Magazine and a contributor to Truth Is Cool and OMNI Reboot. He can usually be found on TVTropes or RationalWiki when not exploiting life and science stories for another blog article.