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Why methane on Mars has reignited our quest for life on other planets

A self-portrait of Nasa's Mars rover Curiosity. It can test for organic compounds on the planet once powdered by the rover's drill. Photograph: JPL-Caltech/MSSS/Nasa
The existence of life beyond Earth is a prospect so profound that few others could be more deserving of Carl Sagan’s caution that extraordinary claims need extraordinary evidence. What else competes? Proof of God? Proof that we are, as an Oxford professor has speculated, hapless characters in a computer simulation?
The announcement this week that Nasa’s Curiosity rover had detected unusual bursts of methane on Mars prompted a flurry of speculation that the gas came from alien life – that microbes on Mars could be churning out the gas, much as happens on Earth.

But as evidence for life goes, methane is not extraordinary.

More than 90% of methane in the air on Earth comes from living organisms. That is because Earth is rich with life. On Mars, the amount of methane floating around is measly: about one part per billion, with bursts reaching 10 times that amount. The entire quota could come from geological processes inside the planet and UV rays breaking down chemicals that arrive on meteorites.

And so the hunt is on to learn more. Here Nasa faces a problem. The Curiosity rover was not designed to spot signatures of past or present life. Rather, its mission is more conservative: to poke, crush and sniff Martian rock and soil to find out whether the planet was once, or still is, hospitable to life. Homing in on the source of the methane – whatever that may be – could take years.

As on Earth, the remnants of past life might be lurking in rocks in the form of microfossils. But again, good evidence will be hard to come by. “Curiosity is a very capable rover, but it isn’t well equipped to interrogate rocks and say is there evidence for life, or past life, in them,” said Dr Carl Pilcher, interim director of Nasa’s astrobiology institute at Ames research center in California.

One instrument on Curiosity, named Sam (sample analysis at Mars), can test for organic compounds in Martian rocks once they have been powdered by the rover’s drill. If mission controllers got lucky, the rover might detect specific, complex organic chemicals that living organisms decay into, but the chances are slim.

“That’s not likely to happen, at least in part because we know that there will be oxidants in the samples. Perchlorate is ubiquitous on Mars, and when you heat up a sample with organics and perchlorate, it oxidises into carbon dioxide,” said Pilcher. In other words, the measurement destroys what the rover wants to measure.

But the Curiosity team could have another way to pin down whether the methane comes from alien life. To boost the sensitivity of their latest measurements, they spent a year collecting Martian air and enriched it by removing all the carbon dioxide. If they can enrich the air even more, they might spot differences in carbon isotopes in the methane. Life on Earth favours carbon-12 over the heavier isotope carbon-13. The signature can distinguish methane made by life and that made by other processes. But again, there is a problem. The process consumes a lot of energy, and Curiosity still has its main job to do: climbing the 5km-high Mount Sharp in the middle of the giant Gale crater to study the planet’s geological past.

No planet beyond Earth is more studied than Mars. But other bodies in the solar system are, if anything, more tantalising for many astrobiologists. Europa, one of more than 60 moons that circles Jupiter, appears to have an ocean of water sloshing around beneath the surface. The Hubble space telescope has seen what looks like a plume of the water bursting out of the moon into space. One proposed mission, Europa Clipper, would fly a probe around Jupiter on an orbit that would swing past Europa to look for signs of habitability. “Europa is of great interest, but it’s in a very intense radiation environment,” said Pilcher. “It’s also deep inside Jupiter’s gravitational well, which means the spacecraft accelerates as it plunges towards Jupiter, so if you want to stay around Europa for any length of time, you need a lot of energy to slow your spacecraft down.”

Another place that excites those searching for ET is Enceladus, a tiny moon of Saturn, just 250km wide. Enceladus has liquid water under its surface too, though some finds its way out. “Enceladus is delivering water to space on a regular basis, and guess what: it contains salts and organic compounds,” said Pilcher. It is not in so harsh a radiation environment as Europa, but it is further away – about twice the distance to Jupiter.

Given the abundance of promising places to search, where should Nasa focus its efforts? “We can’t say what the best candidate is. That’s the beauty of science: it’s unknown. We don’t know what nature is doing out there yet. But what we’re doing is finding out. Nature may be creating life everywhere, and we’ll find evidence for it, or it could be otherwise. We don’t know.”

Curiosity may never confirm the source of the methane plumes it has sniffed in the Martian air. But a follow-up mission, named Mars2020, might. Though modelled on Curiosity, Nasa’s next Martian rover will have an upgraded suite of instruments. Crucial among them is a tool called Sherloc, which can create detailed maps of minerals and organics in rocks. Unlike the Sam instrument on Curiosity, it can look for organics left in rocks by ancient life without destroying them.

But to be convincing, the evidence for alien life must be regarded as extraordinary. That means going beyond chemistry to structure.

“The chances are that there will always be naysayers, but if you found the right chemical remnants, and they appeared in a way that had the structural elements of an ancient cell, and particularly if you found more than one, and even one caught in the process of division, then that combination would be the smoking gun,” said Pilcher.

Nasa set up the astrobiology institute in the mid-1990s, not long after scientists at the agency held a press conference to announce what they believed were signs of ancient life in a Martian meteorite, ALH84001, which fell on to Antarctica.

Few scientists believe the evidence now, but work on the meteorite, coupled with the first discoveries of planets beyond the solar system, convinced Nasa it needed an institute to bring scientists from different fields together to study questions about life elsewhere.

The discovery of life beyond Earth would immediately spark more questions. Did life form on one planet and get carried to others on rocks kicked up by collisions in the early solar system? How then did life evolve in those places? Another possibility is what Pilcher calls n=2: a second genesis of life.

All life on Earth comes from a common ancestor. If we found a second origin of life, we could compare it with the life we know, and begin to understand what is essential for life to exist.

“The question is whether the universe is lively or lonely,” said Pilcher. “Is there life all over the universe, or is life a rare phenomenon? It’s almost as profound to learn that life did not arise in a place that is habitable. Why did it form here and not there?”

Life off Earth

Robotic life: Life on Earth is based on carbon, but on other planets, silicon could take the leading role. Richard Dawkins speculates that just as humans are building robots that might one day supersede us as the dominant species on Earth, the same may already have happened on another planet.

Aquatic aliens: Space telescopes have found planets beyond the solar system that seem completely covered in water. One, Kepler 62f, lies 1,200 light years away. On water worlds, marine creatures could use bioluminescence to communicate in the dark depths, and winged organisms might evolve similar to flying fish, researchers say. Their technology is unlikely to be like ours though, because electricity, fire and metallurgy are problematic underwater.

Ice beings: Frigid moons, such as Europa, orbiting planets far from their stars, could harbour life despite receiving so little sunlight. This year, a community of thousands of different bacteria was discovered in a lake under 800 metres of Antarctic ice. With no sunlight, the bugs broke down minerals for energy. Lewis Dartnell, an astrobiologist at Leicester University, speculates that microbes on an ice world could line up in fibres to extract energy from the magnetic field.

Humanoids: Rather than sentient blobs or little green beings, alien life might look uncannily like us. Simon Conway-Morris at Cambridge University says any aliens out there will have evolved along such familiar lines that they will have eyes and walk on two legs. They will also be greedy and violent like us, he believes.

10 comments:

  1. As it's now confirmed that there's methane on mars and likely had life in the past says something of finding life in the future on the surface of mars. I wonder what causes this episodic increase of methane. As on earth levels of methane are rising and some relate the booms and sinkholes all occurring around the world especially in the Siberian landscape are mysteries scientist still trying to unravel .

    Do they have some relation whats measured by the Curiosity on mars due to some atmospheric changes we see on all the planets in our solar system today?

    I don't know whats causing this but maybe some here could bring some theories that will satisfy my questions around this mystery ..

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  2. Thanks for this exciting news. This has further strengthened my belief that there's Martian life forms underground.

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    1. I think it may have "formed" above ground in Mars' wetter, warmer past (when Mars had oceans and a thick atmosphere), finding its way to all parts and depths of the planet, just as life on Earth has found its way to all niches.

      However, as the planet lost most of its atmosphere and surface water, only the underground life may have continued to survive -- where it may still survive today.

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    2. There is more exotic life on earth, why do microorganisms on Mars make you happy?

      Sure, its life. if the reason.

      but not the extinct civilizations people have fantasized about all this time...

      Every planet has a potential to support life, in some form.. extremophiles give us that reasoning. But not necessarily evolved and intelligent life, which is what the whole fracas is about. more.. well bugs, who have been bugs for billions of years.

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    3. Because if there is life on Mars (any life at all), and if that life could be shown to have its own genesis (i.e., not seeded from Earth or vice versa), then that may speak volumes about the ubiquity of life in the universe.

      That is, if life had two separate and independent beginnings on two planets next door to each other, then that suggests that the genesis of life elsewhere is an extremely common thing.

      It's one thing to say that there must be life elsewhere in the universe because the universe is so big. However, if we then introduce the idea that not only is the universe so big, but it also seems the genesis of life may be a very common thing, then that really changes the landscape of how we look at the potential for other places to have life.

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  3. Pretty indicative of life... but not definitive. But it does add to the likelihood ...with the two (or is it three now?) meteorites from Mars with very possible fossils, the Viking test being positive for life according to the guy who designed it, etc.

    Perhaps Mars, itself, is alive... and gassy.

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  4. I am still in the camp of thoughts that there WAS life on Mars and there still possibly IS life on Mars, though I am thinking the current life is possibly microbial. I think the past life on Mars, was possibly humanoid. I have been reading comments from a Dr. John Brandenburg Ph.D who has been studying the Cydonia plain area including the famous Mars face, and he has concluded there was no reason to think they were artifical. He has a background in atomic weapons research and he is thinking isotopes in the Martian soil and atmosphere suggest that a huge nuclear explosion one which was capable of wrecking the entire planet took place in the northern hemisphere of Mars millions of years ago. I find this fascinating, and am open minded of all the possibilities for this type of thinking.

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  5. The question-- is Mars' methane due to living things, or merely geology? May be answerable. Methane produced by life should have much more carbon 12 relative to carbon 13 than if it came from the decomposition of minerals. A mass spectrometer is needed to check these isotope ratios.
    Fortunately, the Curiosity rover has such an instrument. The detection of methane we are now hearing about was done with a different instrument, so the question must remain unanswered for the moment.
    At only 7 parts per billion, let us hope there is enough methane for the mass spectrometer to work with, so that it can be used to tell us if there is life on Mars.

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  6. The next rover being sent to Mars, Mars 2020 will likely seek an answer to the question of where the methane is coming from if we do not figure it out from data Curiosity has collected/is collecting.

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    1. Further inquiry reveals that Curiosity's mass spectrometer can not do isotope analysis at methane levels below tens of parts per billion. So, unless a much larger burst of methane comes along, it looks as if the Mars 2020 mission is the best hope for resolving the source of the methane.

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