Discussion and news about the modern effort to understand the nature of life on Earth, finding planets around other stars, and the search for life elsewhere in the universe

Wednesday, November 24, 2010

The ten most important questions for astrobiology: Number 1

As our year approaches its end, with the planet slithering ever closer to where it was 12 months ago and towards its closest approach to the Sun on January 3rd, it seems like a good time to indulge in a highly biased and incomplete bit of rumination. There have been many tremendous discoveries and advances this past year, each inching us closer to tackling some of the core questions about life in the universe. Nonetheless, lots of big and important questions remain. Some approach the philosophical, some are quite narrow, but they're all interesting, and many overlap greatly. I thought I'd do a series of posts on the ones I particularly like, you may agree or disagree with the choices - a reasonable and necessary part of the process - but hopefully they will stimulate.

Number 1 is relatively non-challenging: Are there other planets like the Earth?

We're much, much closer to answering this than we were a year ago. As surveys for exoplanets increase in sensitivity, sample size, and sampling time it appears that small rocky worlds are essentially ubiquitous. With statistical estimates that at least 1 in 4 Sun like stars harbor Earth-sized planets within their habitable zones (extrapolating from shorter period objects) there is good reason to believe that Earth mass planets in comparable orbits are definitely out there. Kepler will help nail the rates to the wall. It will remain a tough question to tackle at a deeper level though. 'Like the Earth' is a bit ambiguous. Mass and orbit are one small piece. How many of these worlds have comparable chemistry, geophysics and climate? A good bet is that there are numerous cousin planets, recognizable but nonetheless a bit alien. That may of course be just fine. We're awfully biased about ourselves, often without recognizing the fact. One of my favorite mantras is that the modern Earth is not typical of our homeworld throughout its history. The suitability of the Earth today for life is a poor template to use.

So, if we treat 'like' as a broad qualification then the answer is almost certainly yes, and in another 12 months we'll have even better evidence supporting this.


kurt9 said...

In another 12 months, we will have statistically meaningful data about the presence of Earth-sized planets in desirable orbits around their stars. We will know nothing about their atmospheres and other characteristics. It seems to me that a space-born platform like TPF should be about to spectroscopically image the atmospheres of Earth-sized planets within, say, 30 light years of us to find free Oxygen atmospheres. If such exists, it is reasonable to say that Oxygen producing photosynthesis is occurring on that planet. It is, of course, about 10 years before we have the instrumentation to do this.

Anonymous said...

A lot of science reports in popular press about bacteria living deep within the earth and their potential role in oil and gas production. Some speculation that oil and gas are continuing to be produced by some yet unknown biochemistry. Given the high temperature and pressure inside the earth where these organisms live one would have to think we may need to redefine our definitions on conditions that can support life. This brings us back to your comments about biased views. Will these "inner earth" studies dramatically alter our view on the possibilities of "off earth" life.

Caleb Scharf said...

Re the comment about bacteria and subsurface life. Absolutely. It's now clear that the major part of the biomass and genetic diversity of life on Earth is in the subsurface, especially in the oceanic sediment and crust (you can check out my 'shadow biosphere' post at Discover magazine). Having said that, from the point of view of finding planets with clear outward signs of life then looking for 'Earths' still makes a fair amount of sense (with the proviso that it may not be the modern Earth). It's not yet clear how much our subsurface biosphere truly influences the immediate outward characteristics such as atmospheric composition etc. It's also true that the presence of large amounts of liquid surface water and oceans seems to play a key role in the nature of modern geophysics, i.e. plate tectonics etc. that subsurface life probably has some dependency on. So looking for 'water' planets still makes sense.

kurt9 said...

Deep, hot biospheres are real. But its hard to detect them by astronomy and its all prokaryote life anyways. Detection of free Oxygen atmosphere ought to be strong indicator of photosynthetic life and Eukaryote life at that. I don't think this can be done with ground instrumentation. It probably requires a space-based platform like TPF or something similar.