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.

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.

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 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.

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.

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 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.

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 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.

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.

Carole Mundell is Head of Astrophysics at University of Bath.

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

Washington (dpa) – A NASA spacecraft was on course on Tuesday to make a flyby within 520 kilometers of Saturn’s moon Dione – its fourth flyby since the spacecraft Cassini went into orbit around Saturn in 2004. A fifth flyby of Dione is planned for August, before Cassini’s final mission begins late this year. It will… Continue reading →