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

[Graymalkin]

Hence the line about "light gathering chemicals like it". There's a few different chemicals that can be used by organisms in photosynthesis. Chlorophyll is simply the most popular on the surface of the Earth. Other pigments are optimum for regions that receive different light spectra than the surface. On worlds whose stars had different spectral maxima than Sol these pigments would likely be more abundant in photosynthetic life.

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.

[Travis Mansbridge]

Soon we may need another habitable planet whether the locals like it or not.

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.

Re:But should we go.

[i kan reed]

Bacteria evolved to eat the completely artificial substance of nylon. I'd rate the scenario as "plausible"

Re:But should we go.

[meta-monkey]

These are the kinds of questions that absolutely fascinate me about exobiology. If we discover life on another world (maybe even in our solar system) and it turns out to be completely different from life as we know it, that would be amazing, to study a completely different biology. If we find this life and is just like us, that would be equally amazing, because it would hint at common origins or common processes to the formation of life everywhere. Even if we find no other life, that's amazing, because it shows how unique we truly are.

Basically, every discovery or lack of discovery regardless of outcome in exobiology is amazing. You can't go wrong with that science.

Re:But should we go.

[InsultsByThePound]

He means Sarah Palin. Now proceed to your scheduled waterboarding baptism. Yee-haw, muddafukka.

Re:But should we go.

[CreatureComfort]

I think it all depends on how tasty that alien life is...

Re:ATLAST

[Trapezium Artist]

Absolutely right: I was going to point out the same thing. It's many, many years away from any possible launch ...

For reference, the James Webb Space Telescope (or NGST as it was then) was beginning to be picked up as a serious prospect by NASA, ESA, and the Canadian Space Agency in the late 1990's. It's due for launch now in 2018.

(This is not meant as a criticism: I've been closely involved with JWST since 1998 and know how hard it has been in terms of technology, programmatics, and politics to get the good state it's in today, namely mostly built and now entering the comprehensive integration and test phase.)

So, very crudely, I'd say that something like ATLAST might be launched after 2035, if it gets picked up as the highest priority in the next US astronomy decadal survey.