We’re getting close to the day when we’ll spot an Earth-like planet orbiting another star. Astronomers have already seen a number of superEarth candidates–rocky planets in the habitable zone that are many times larger than Earth. They’ve even begun to analyse the atmosphere of these places and got some idea of what it might be like on their surfaces. Earth-sized planets won’t be far away now.
But if we are to spot the signs of life on these bodies, what should we look for? The European Space Agency has been giving this some serious thought for a mission called Darwin currently pencilled in for launch in 2015. It’s goal is to look for signs of life on Earth-like planets.
Today, the team behind the mission explain some of the reasoning behind their design for the spacecraft. To look for life, they’ve had to make some important assumptions about the form it might take. For example, they’re plumping for carbon-based life forms that rely on water as a solvent. Fair enough but their assumptions go a lot further:
“We assume that extraterrestrial life is similar to life on Earth in its use of the same input and output gases, that it exists out of thermodynamic equilibrium, and that it has analogs to microorganisms on Earth.”
That’s getting pretty specific but they say their hand is forced by the fact that they’ve never seen any other type of life and so can’t possibly know what else to look for.
So Darwin will look for carbon dioxide, ozone and of course water in the atmospheres of these planets as well as methane and ammonia.
Finding those in the right abundances will be good evidence that something interesting is happening on these planets although finding any other gases that are out of geochemical equilibrium will also be an eye-opener.
The trouble is that finding these signatures will by no means be a slam dunk in favour of life.
In one of the classic scientific papers of the 20the century, Carl Sagan and colleagues published their analysis of the data from the Galileo spacecraft’s 1990 flyby of Earth. The spacecraft saw all those gases and more. Their conclusion? “Our results are consistent with the hypothesis that widespread biological activity exists…on Earth”.
Not quite conclusive and that’s from a distance of a thousand kilometres. So it’s hard to imagine that data from Darwin could provide conclusive evidence of life at a distance measured in dozens or hundreds of lightyears. But I guess that’s nothing a good PR team couldn’t solve.
Ref: arxiv.org/abs/0805.1873: Darwin – A Mission to Detect, and Search for Life on, Extrasolar Planets
Already two years ago the ESA science director confirmed to me that Darwin had been taken out of ESA’s planning – the technical hurdles were deemed just too large. And indeed, the mission is absent from all detailled longterm planning charts ESA is showing today. Something like Darwin might fly eventually, but certainly not before 2020 and perhaps as a joint venture with NASA where similar independent plans (“Terrestrial Planet Finder”) have also been put on hiatus.
Thanks Daniel. Somebody ought to let the Darwin team know too.
The chance that there is life elsewhere, especially complex life, intelligent life, is extremely small. It takes a book to go through all the arguments, but they are overwhelming:
Our Almost Impossible Universe:
Why the laws of nature make the existence of humans
extraordinarily unlikely
R. Mirman
Don’t waste time on daydreams when there are so many fruitful research projects.