First, my apologies for being away from here for so long. I promise to be more attentive from now on. Next, I want to take this issue to express some of my own observations and opinions as we are now on our way to find Earth-like planets in our galaxy.
Much of my comments are more relevant to those follow-on explorations after Kepler has brought home a list of likely candidates. Kepler, by design is not intended to discern if there is life on a discovered exo-planet. Its primary mission is to find the ideal combination of star and planet that fits the Earth profile. I am confident Kepler will fulfill that goal several times over.
In my related blog, ExoDigest, I have included links to articles and reports that indicate that our scientists are still quite busy seeking answers to how life originated on this planet. The obvious corollary is that until we understand our own beginnings it will be hard to determine the presence, stage and status of life forms on any Earth-like exoplanet. This leads me to the question. How Earth-like does our candidate exo have to be?
Well, we know that its distance from its host star (the habitable zone) is important to insure that the planet has and sustains water, and it is not too hot or too cold. So water too, must be a basic ingredient as well as a variety of gaseous chemicals (oxygen, hydrogen, helium, carbon dioxide, nitrogen and a variety of combinations of those chemicals). Certainly, the orbital period of our candidate around its parent star is important but equally important is the planet's rotation around its own axis. The cycle of light and dark are known factors the affect how things grow and thrive. It is also helpful for a "rocky" planet to have healthy gravity in order to keep a grip on all of its important life support components. The list is much longer and even includes new research that indicates that tectonic plates are contributors to the development of life. So, as astrobiologists state, this is not going to be an easy task.
Back to my question. I repeat, until we know completely how life got its start here, it will be difficult to determine if life on another planet has started, will start or started and stopped. In the latter case, our exploration of Mars is going to help us understand why life started and stopped, and why that planet also apparently lost much of its atmosphere and life supporting gases. Was it knocked so silly by an asteroid impact that it lost its life giving/supporting elements? We need to know this both for our appreciation and protection of our home, and in investigating candidate exoplanets.
I think there is going to be at least a century of awesome surprises that will tell us not only how we got started, but may indicate that starting up life has a variety of paths and that ours is not exclusive. Add to this the evolutionary process which as part of the development of life and is still part of our own mystery. For example, would we even be here, if the dinosaurs had survived? Planet age is also going to be a factor. How old was Earth before life got started, and is this a universal requisite or could life actually develop faster or even slower than it did here?
Well, it looks like it may be our great grand children or even our great, great grandchildren who finally get most of the answers. It will also be even longer before there is ever any direct association between life here and life on another planet. The distances are immense, even at the speed of light. At this realization, some may say, "why bother?" The answer is simple, in my mind, we bother because it is a genetic imperative. The next evolutionary step for us is to do exactly what we are doing. By reaching out to finally know we are not alone is going to dramatically impact who we become and how we deal with it. We will suddenly feel far less important while at the same time feel excited to be part of truly universal life. The universe, itself, will take on new meaning and become open to new avenues of research. Did it start with a bang, and will it end or...? Most importantly, we are now moving down the path that will open whole new revelations and opportunities to fully understand, appreciate and respect all life as well as the uniqueness of humankind within that environment.
I end here, and ask: "Quo Vadis ?"