After the jump, my review.
Given the success this week by NASA of safely landing the Curiosity rover on the surface of Mars, it seems like an appropriate time to read and review The Life of Super-Earths: How the Hunt for Alien Worlds and Artificial Cells Will Revolutionize Life on Our Planet, by Dimitry Sasselov.
Dimitry Sasselov is a Harvard astronomer, not a professional writer, but he does a creditable job in writing a science book for a general audience. The pairing of subject matter -- the hunt for Earth-like planets elsewhere in the galaxy and the study of the origins of life on this Earth -- struck me as odd when I first cracked open this book (and by "cracked open" I mean, of course, downloaded from the Richardson Public Library. Thanks, RPL). What does peering through telescopes at other stars have to do with peering through microscopes at amino acids? It turns out, quite a lot.
Sasselov is at his best describing the work he is most familiar with, the effort to find extra-solar planets. The technical challenge this poses is that the brightness of stars makes it all but impossible to see dark companions in orbit around them. Astronomers pull out all the tricks in their book to detect planets. They look for wobbling stars, suggesting the gravitational tug of planets. They look for periodic dimming of star light, suggesting planets passing in front of the star. As astronomers' skills improve, they are able to deduce smaller and smaller planets. No Earth twin has been found yet (same size at a habitable distance from its sun), but more and more super-Earths (rocky planets of one to ten Earth masses) have been identified. As it turns out, super-Earths are probably more likely to harbor life than Earth-size planets are.
Sasselov lays out what he believes are the requirements for life -- rich chemistry, steady energy sources, and relatively low temperatures. These requirements probably limit the existence of life to planets. He goes on to explain why super-Earths may be better able to provide the needed environment -- atmosphere, water, tectonic plate activity to stir up the chemicals needed -- than Earth-size planets. And so, the growing number of super-Earths being found by astronomers gives hope that we really are not alone in the universe.
Sasselov makes the case that life can form early in a planet's life cycle, and once established, is practically indestructible. Earth is four billion years old and life has existed on it for 3.5 billion years. Sasselov suspects that humans have already, unwittingly, transported microbial life to other planets (the Mars missions) and perhaps even insterstellar space (the Voyager missions). Sasselov is confident that Earth's life has a good chance of surviving even long after our own Sun has burned itself out. Given that the universe is still relatively young (13 billion years) and we can expect it to be hospitable to life for a hundred billion years or more into the future, Sasselov expects life to propagate wide and far throughout the galaxy.
This is a short book. It's an easy read for non-scientists. The curious pairing of subjects could be Sasselov's attempt to justify why scientists are interested in extra-solar planets too far away to ever visit, but if so, he succeeds. The Life of Super-Earths does inspire deep thoughts about life, ourselves, and our place in the universe, now and long into the future.
"Today we stand on the threshold to new worlds -- planets that we could call home, planets that someone else might call home already. The search for them has spawned a new space race: the race to discover an Earth twin planet."
"With all these fractional reductions to the population of 200 billion stars in our Galaxy, I end up with 100 million planets with habitable potential today. This number is not precise, but there is no escaping how big it is."
"The actual origin of life on Earth remains as elusive as ever and may well stay that way. After all, it is a historical question that requires knowing environments that are not preserved in the Earth's geological record."
"As fragile as life may appear to be, clinging to the surface of a small planet that is subject to violent cosmic events, what we have learned has led us to conclude that life on Earth is virtually indestructible."
"When Earth was being bombarded by asteroids early in its history, the outflow of material would have been nearly as great as the inflow, and it's not hard to imagine some of that material being life, ultimately to travel interstellar distances, embedded in dust particles or comets, until it found a new home on some other habitable planet."
"Increasingly, we plan for the future as a society. This capacity -- underlined by our ability for abstract thought that can reach beyond the horizons of space or time -- is perhaps our most remarkable trait. Microbial life may be able to survive most of the slings and arrows the Universe can throw at it, but as we've seen, the Sun will someday put an end to life on this planet. If anything will enable life to endure past the limited lifetime of the planets, it will have to be our ability to think."