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.