Boffins develop interstellar alien ocean-spotting tool Astronomy boffins say they have developed new techniques which could use the space telescopes of tomorrow to detect oceans on alien worlds orbiting other suns. Earth as seen from Voyager 1 some four billion miles away. Credit: NASA JPL Earth as an alien invasion/harvest fleet would see it. As all regular Reg readers will …
The physical size of the crescent Earth as seen from that distance was smaller than one pixel, the reflected light was bright enough to register across a single pixel.
And El Reg...
If you're going to use the 'pale blue dot' meme, it's worth linking to Carl Sagan's commencement address where he used the phrase for the first time. It's a wonderfully evocative piece of prose:
http://en.wikipedia.org/wiki/Pale_blue_dot#Reflections_by_Sagan
Lewis,
After reading that article, I was sorely tempted to suggest and advise that you change your medication, but then thought better of it, as it would need to be addressed to NASA Boffinry instead.
Fine mad reporting is it then yours to claim. :-)
So, basically, scientists are looking for lifeforms that exhibit the same traits as Earth-originated lifeforms; that is to say, they must require, or originate from, water.
What about lifeforms based on other elements or compounds? What about lifeforms that can only survive in pools of liquid Hydrogen, for example? There's plenty of planets cold enough for that!!
Perhaps NASA just want lifeforms on planets the Americans can send soldiers, politicians and McDonald's franchisees to....
"there are some weird scenarios you can dream up that don't involve oceans but would lead to varying patches of blue on a planet, but these are not very plausible."
There are a lot stars out there, many of which will have planets, some of which will be in the "could have water" zone. I am sure that on some of them them, the "not very plausible" will occur.
...to get an outside point of view takes a whole old meaning now.
I wonder if they should have tested every "life detection probe" that fashion. Make it orbit, make it land back *anywhere* and test for life, even if it falls inside [name of active volcano here]. It should alarm positive except when landing in molten lava.
Light collection should scale with area. To get a million times more area we need to scale radius up by thousands -- i.e. a mirror kilometers across. Much easier, but to do it in space might not be so easy unless you can make a mirror out of reflective film and rotate it to keep it spread out; whilst somehow controlling its shape. Oh yeah, with a separate space craft maneouvred accurately to the focus to take pictures.
I've read the paper and their result looks robust, but there's nothing really quantitative about how to apply it to exoplanets, there's basically just a throwaway sentence "we conclude that it should be possible to infer the existence of water oceans on exoplanets with time-resolved broadband observations taken by a large space-based coronagraphic telescope." Hmm.
OK then put in some numbers. Their imaging is done at ~0.5-1.0 microns, at which wavelengths the Earth is about 1E10 times fainter than the Sun, so at 10 parsecs the Earth would be about 30th magnitude. For this technique to work you need to image a few times a day to see the rotation - you can't just sit on the target for a long time to build up S/N.
So, ballpark, we want to get a 30th magnitude target at optical wavelengths in an hour. For comparison, the Hubble Deep Fields get to about ~29th magnitude at these wavelengths with 1E5 second exposures in each band, and a 2.5m mirror. So with S/N proportional to sqrt(time) that's about 27 mag in an hour with 2.5-m mirror, we want to go three mags deeper which is a factor of 15, which gives a ~10-m mirror (S/N proportional to D^2). That might be on the small side depending on how strict we are with our S/N requirement. Anyway - big, but not technologically impossible.
However this does assume that you can blot out the light from the 5th mag star 0.1 arcsec away!
One of the primary reasons that planet hunters are aiming for the IR rather than the optical is that the contrast between star and planet is "only" about 1E6 rather than 1E10. I'm not sure how easy it would be to divert their attention to short wavelengths...
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