Caleb Scharf and Lewis Dartnell on the guessing game about the possibility of life on Mars
Is there life on any other planet? A question that has held the imagination of many finds discussion in the wake of news from Curiosity that says it has found evidence of chlorine, sulphur and water, and of organic compounds on Mars. But the doubt remains as to whether the compounds really come from Mars or whether they hitched a ride onboard Curiosity all the way from Earth. Adam Smith interviews Caleb Scharf and Lewis Dartnell to understand the quest for life on planets other than Earth.
“...there will be further missions to Mars and to other places...of trying to go back to Saturn, to land on Titan. Titan is a radically different environment than any we’ve seen but there’s a possibility that there could be some sort of life there, but it would be extreme, it would be truly alien,” says Scharf, from Colombia University, New York. “In our own solar system there are many moons around giant planets that are coated in water ice. Europa around Jupiter is a great example and Enceladus around Saturn is another... there’s been a long suspicion, because there’s lots of water and because you go deep enough, it may get a bit warmer, those are potential habitats for life...might be the sorts of things that live in the ice of Antarctica. They might not be identical organisms but the speculation is that organisms on Earth have found certain chemical tricks to survive. The same sort of tricks might apply somewhere else in our solar system. Those chemical tricks leave behind traces, so there you have a situation where the microbiologist and the astronomer or planetary scientist can sit down and have a conversation and say, what should I be looking for.”
Scharf is an astro-biologist. Talking of the relatively new field of astrobiology, he says, “Back in the early 1990s, NASA had this sort of sudden revelation that the search for life in the universe was a big and important thing... So out of that came the modern Mars exploration programme. So in that sense NASA has poured billions of dollars into astrobiology. Astrobiology has become the motivating science behind most of NASA’s robotic exploration of the solar system and planets.”
With that as the focus, the next question is, does Curiosity’s news make us suspect life on Mars? Lewis Dartnell from University College, London says, “Finding organic molecules on Mars does not mean we’ve found evidence of life. It means we’ve found the kinds of chemistry you need to make life. So scientifically that is incredibly exciting... Water has helped sculpt the Earth and we think, or we had thought, hoped, speculated that it had helped sculpt Mars...life on Earth is utterly reliant on water...and so we think you need water, you need it in a liquid form, if you’re ever going to have living organisms.”
Scharf stops you from getting too excited by saying, “Right now, Mars is a pretty hostile place, the atmospheric pressure on Mars is less than one thousandth of what it is on Earth, so you can’t breathe on Mars, it’s like a vacuum, it’s bad news. With a thin atmosphere like that, water quickly turns into a gas on the surface, it doesn’t sit around as a liquid...So the fact that water really did once flow on the surface of Mars tells you a number of things. It tells you there was plenty of water around, there’s a lot of water we know frozen in Mars, beneath the surface, but it means that at some point it was on the surface, even if only temporarily. And that tells us something about the atmospheric conditions. ..so the discovery of flowing liquid water on the surface of Mars suggests that some time in Mars’s past the atmosphere could have been different, the temperature could have been different, the environment could have been very different — warmer, much more like that on Earth.”
Alas! Mars we are late!