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EPOXI Team Develops New Method To Find Alien Ocean
Matt_dk writes "Astronomers have found more than 300 alien (extrasolar) worlds so far. Most of these are gas giants like Jupiter, and are either too hot (too close to their star) or too cold (too far away) to support life as we know it. Sometime in the near future, however, astronomers will probably find one that's just right — a planet with a solid surface that's the right distance for a temperature that allows liquid water — an essential ingredient in the recipe for life. Now scientists looking back at Earth with the Deep Impact/EPOXI mission have developed a method to indicate whether Earth-like extrasolar worlds have oceans."
why should water be essential for life?
Because nothing truly brings out the flavor of a fine Scotch like a drop of water.
As far as I know, most of the techniques used for detecting exoplanets depend on the planet being ~Jupiter mass and pretty close because then
-you get gravitational "wobble"
-you're more likely to be in line for a transit
-mass is enough for gravitational lensing
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and how do you define life anyway?
Good question. There's lots of ways, but my personal preference in this context is a system that expends energy in order to combat entropy. Once you stop combatting entropy, you head towards thermodynamic equilibrium, and are dead. This definition may be overly broad (by that definition, my computer's memory chips are alive), but I suspect that if we find something that meets these criteria, it will be associated with life.
What are the alternatives? Carbon-sulfur might be a reasonable option. Silicon-oxygen is a little further out. There are only so many atoms available, and their prevalence is dictated by stars, so that puts a limit on what variations could be possible, and, well, there aren't that many.
I just wondered something. Generally, the presence of condensed phase liquid water is considered a marker that tells us "Look for life here." Unfortunately, given our current technology, most planets we find are gas giants that orbit too close to the star to be in the "habitable zone". But gas giants, by virtue of being huge, have hugely high atmospheric pressures in the lower atmosphere. Couldn't supercritical water (i.e. water at a sufficiently high temperature/pressure that there is no distinction between gas and liquid) support life? Or, for that matter, supercritical methane, or any other supercritical medium? After all, we can run useful chemistry in supercritical fluids such as supercritical CO2. And if it can support life, wouldn't the possibility of life in supercritical water significantly extend the habitable zone?
You raise a common question: why not look for life as we do not know it? Why are we looking for something so darn Earth-like?
Yes, life could exist elsewhere. There are soooo many possibilities. I mean, we seem pretty distance-from-the-star-centric, but even on Earth some critters aren't solar-energy dependent! Did you know Jupiter radiates more heat than it gets from the sun?
But basically, here's why we're looking for Earth-like planets:
Big gas giants are 0 for 4 on having life (that we know of)
Objects that do not revolve around a star: 0 for many
Small rocky planets: 1 for 4
Rocky Earth-sized planets that are 0.9-1.1 AU from a medium-sized star: 1 for 1
We have limited resources, so we are forced to narrow our scope. Narrowing our sights based on the few dozen studied objects in our solar system... it's easy to mock, but what else can we do? We can (1) keep searching through our own solar system to ameliorate some of the "sampling bias," and (2) look for rocky Earth-sized planets that are 0.9-1.1 AU from a medium-sized star. And that's pretty much what we're doing.
Even on earth, the study of lithotrophs ("rock eaters" that get energy by oxidizing inorganic materials) is a decades-old field. They are found in all sorts of settings, though not a significant part (by mass, not necessarily by importance) of the biosphere. Many lithotrophs even engage in carbon fixation from CO2 using the energy they derived from "rock eating", and thus can live completely independently of any need for photosynthesis (even by other organisms). As for lithotroph metabolisms, your imagination is the limit. Lithotrophs even have commercially viable applications. Anaerobic oxidation of ammonia by nitrite, a reaction performed by certain "anammox" bacteria, is useful for the treatment of fertilizer-contaminated waste water.