Astronomers Calculate How To Spot Life On an Alien Earth

KentuckyFC writes: "One of the main goals of the space program is to spot an Earth-like planet orbiting another star. And by Earth-like, astronomers mean a planet with liquid water, gaseous oxygen and even chlorophyll, or a light-harvesting molecule like it. The biosignatures of these molecules were all observed during the first Earth fly-by in 1990 when the Galileo spacecraft measured the light reflected off Earth as it flew past on its way to Jupiter. But if these biosignatures exist on more distant exoplanets, could we spot them today? Now astronomers have calculated how good the next generation of space telescopes will have to be to pick up these biosignatures of life. They say that gaseous water should be relatively straightforward to pick out and that oxygen will be more challenging. But the spectral signature of chlorophyll-like molecules will be much harder to spot, requiring significantly more sensitivity than is possible today (either that or a great deal of luck). That suggests a plan, they say. The next generation of space telescopes should look for water and oxygen on exoplanets orbiting nearby stars and only then begin the time-consuming and expensive task of looking for chlorophyll on the most promising targets. One spacecraft that might do this is the Advanced Technology Large-Aperture Space Telescope or ATLAST that is currently scheduled for launch in the 2025-2035 time frame."

Comments

Chlorrophyll makes a big assumption

[i kan reed]

Isn't chlorophyll tuned to the easiest bands of energy that come from our sun and don't get scattered by our atmosphere? Wouldn't a slightly different stellar color or atmospheric makeup dramatically change how stellar energy would be chemically captured?

Re:Chlorrophyll makes a big assumption

[Dimwit]

It's not so much a big assumption as it is a starting point. There is probably a biosphere somewhere in the Universe that uses a red or yellow pigment for photosynthesis. The problem is that detecting it at a distance is much harder, because while we might see the spectral signature we couldn't be sure that it's life.

Looking for a biosphere that is very similar to that of Earth makes it much more likely that we'll be able to detect that it is in fact "life" and not something else. While we may miss 99% of the life in the Universe with this approach, if/when we do detect it, our confidence will be much higher.

Re:Chlorrophyll makes a big assumption

[dpilot]

ISTR that chlorophyll is essentially a "voltage doubler", basically for red light. (Leaves are green because they use the red, and discard/reflect the green.) If you consider red to be between 600nM and 700nM, then a little more UV than we get might deliver enough content between 300nM and 350nM to be used directly for photosynthesis. I wonder how much UV would be needed to bypass the doubler, and if that would be too much for life, in general. Of course that would mean a hotter sun than ours, and I've more recently heard more about searching around red dwarves, where the leaves would more likely look black.

Re:But should we go.

[newcastlejon]

That assumes the wayward bugs can metabolise anything on an alien world. Things like basic sugars, which I would assume are simple enough to be common, probably. But infecting a totally alien organism? Probably not.

Take staph. aureus for example. It can survive on humans of course, and a few domestic animals (maybe due to their long association with people) but apart from those I understand that it isn't common in other species. A bacteria that can easily cross species lines is one thing, but making the jump to an alien biology is quite another. Then again the biology might not be so alien if they're looking for worlds where the native plant life just happened to evolve chlorophyll.