Five Billion Years of Solitude
The Search for Life Among the Stars
Lee Billings 2013
Another "skim" book from the library, I did not read half of the book. I was looking for improvements to the Drake equation, incorporating recent pessimistic results from astrobiology, but did not find them here. I eagerly anticipate David Waltham's "Lucky Planet", due in May 2014, which adds yet another set of pessimistic probability factors to the Drake equation, added to the extra factors in Ward and Brownlee's "Rare Earth".
In 2013, we really don't have the technology to cost-effectively look for evidence of life around other stars. That could change, with cleverness or new capabilities, so the design of TPFs - Terrestrial Planet Finders - is a worthy activity, even if it only results in heartbreak. Perhaps the best reason for these attempts is that they lead to lateral thinking that can solve other problems. Those new solutions and the capabilities they create may someday make TPF startlingly easy - or else show that it is a waste of time, that we are very unlikely to find life-bearing planets in any solar system we can observe. Either way, it is important to stretch in that direction, because it would be terrible to abandon the quest if we missed some world-saving technology.
The separation of unambiguous lifelight from starlight may not be possible without an unambiguous definition of life itself. Some claim that very small amounts of methane in the Martian atmosphere are signs of life deep underground; whether this is the case or not, we can't decide the issue until we actually look underground, on Mars. We will do that anyway, sooner or later, for many reasons. So arguing about disputed measurements and disputed interpretations is probably a waste of time. Very scarce photons from planets next to giant thermonuclear spotlights - likened in the book to an unlit match-head next to a nuclear bomb explosion, can't help but being quintillions of times more ambiguous.
Billings tells us that the Hubble Space Telescope stemmed from the "civilianization" of spysat technology, and others point out that classified astronomical results from the spysats were verified and "laundered" through HST. Billings mentions a new effort to declassify the technology for 10 to 20 meter adaptive optic spysat telescopes, which may already be in geosynchronous orbit - such mirrors might be good enough to detect atmospheric chemistry on planets around stars within a few light years of us.
However, if detectable life is only semi-common; say 100 million out of the galaxy's 100 billion stars - then the nearest of these planets is a LONG way away, sending very few photons our way and angularly far too close to its star to detect without 1/10th-wavelength-accurate mirrors as big as the moon. Such mirrors would need to be far beyond the Kuiper belt to avoid gravitational distortion from Jupiter.
An object that big would intercept many kilograms of interstellar meteoric material per second. In the same way that the Earth and Mars have exchanged millions of tons of meteoric material over millions of years, if life is abundant enough in the galaxy to change atmospheres we can see, so is the ejected mass, and only a few attograms of frozen bacterial fragments would be enough to demonstrate exostellar origin. Finding those attogram needles in a kilotonne haystack of captured material would require heroic efforts - or atomic precision machines made in Avogadro's number quantities. That can be the result of exponentially scalable technologies, and we already have both carbon and silicon examples of that.
Ambiguity can plague us in other ways. Life as we know it is a fast track to entropy, creating a smidgen of chemical disequilibrium while turning teramoles of optical photons into infrared. There may be much more efficient ways to turn sunlight into heat, and the Earth lacks the elemental combinations that facilitate this. Perhaps some of these ways also create atmospheric disequilibrium, without engaging the minor entropic reversals that life temporarily exhibits. As much as we like to define life as something special and highly organized, the chemical entropic difference between a block of wood and a block of lignite is trivial, and most other planets may have ways to create detectable disequilibrium without our slight entropy deficit. We have only one example of shallow counterentropy - earthlife - and it is as presumptuous to assume that life is the only kind of entropic fasttrack as it is to assume that life is common.
That said, some kind of life probably is common. But as Waltham points out in his papers, climactically fragile multicellular life is dependent on an exquisitely tuned double-planet system like the earth and moon in something like their current mass ratio and spacing. Without that, and plate tectonics, and the rare combination of supernova explosions that seeded the solar system, earth would only have archaea, for a brief fraction of the earth's actual span. As Billings tells us, only a small portion of the Earth's span exhibited biogenic atmospheric oxygen, and without our active beneficial involvment, the oxygen will go away after an even smaller portion of the earth's future span. There may be many earth-sized planets in the "Goldilocks" zone, but we will only know from our own experiments and simulations with variant chemistries and energy arrangements, how many sisters our own Goldilocks has.
The next discoveries will be in the lab and in the computer, not seen through telescopes big or bigger. Theory tells us where and how to look, and without a strong theory, we will build the wrong instruments to look for the wrong phenomena. In a way, we dodged a bullet when we cancelled the James Webb Space Telescope. Omaging putting in another 20 billion dollars and launching it, only to have some underpaid lab rat demonstrate that there was no way it could achieve its objectives. Big instruments often demonstrate only a stubborn lack of imagination and flexibility.
My own prejudices, repeated elsewhere on this wiki, is that the fastest, cheapest, and most reliable path to the future is to pursue small and numerous, not big and unique. Life itself is small, with only a few quintillion multicellular lifeforms distracting us from the far more numerous single celled ones, which are themselves composed of millions of molecules and billions of bits of information. Our electronics and information technologies are steadily converging towards those exquisitely evolved nanomachines, but we have a long way to go. We will image and sample the universe with vast clouds of mechanisms too small to see, rather than a few gigantic soviet-style megamachines, as fragile and inflexible as they are runuously expensive.
It is most likely that life will spread to the universe from the Earth, and our most important task is making sure our rare and precious planet remains alive and healthy long enough to do so. The know-how will come from many efforts, including the efforts to image the rest of the universe, but we will learn little if all we do is multiply sizes and budgets by big numbers.