Newswise — In the late 1990s, the University of Washington created what was arguably the world's first graduate program in astrobiology, aimed at preparing scientists to hunt for life away from Earth. In 2001, David Catling became one of the first people brought to the UW specifically to teach astrobiology.
Catling, a UW professor of Earth and space sciences, is the author of Astrobiology: A Very Short Introduction, the 370th offering in the Oxford University Press series of "very short introduction" books by experts in various fields. Catling was commissioned by editors to write the book, which was published in the United States on Jan. 1. Following are his answers to some questions about the book and astrobiology.
Q: The thinking about astrobiology has evolved greatly in several decades. What is the most important thing you would like the reader of this book to come away with?
A: D.H. Lawrence studied the beliefs of southwest Native Americans in the 1920s and tells us that their one underlying responsibility was to "acknowledge the wonder." I hope someone reading my book will end up acknowledging the wonder of life and our place in the universe by learning what modern science has to say about the topic.
Q: You list nine places in the solar system other than Earth where life might exist today. Which do you think are the most likely candidates?
A: I have the slightly renegade opinion that the best places to look are in the outer solar system, in particular Enceladus (a moon of Saturn) and Europa (a moon of Jupiter). Mars is an excellent place to look for traces of extinct life, but it's probably a long shot for finding living organisms because today it's exceedingly dry. Liquid water is the key to life as we know it. Enceladus and Europa are covered in thick ice and so might not seem promising. But there's evidence that a huge ocean lies beneath the surface of Europa that may be up to twice the volume of all of Earth's oceans.
Meanwhile, Enceladus appears to have a large sea beneath its southern pole, which is pressing up from below and cracking the icy surface. Plumes of icy particles containing organic molecules stream from fissures into space, and they could include extraterrestrial microbes freeze-dried by their ejection into space. A spacecraft could fly through the plumes of Enceladus and bring samples back to Earth. Europa also has towering plumes of water vapor that could be sampled similarly.
Q: How important is the study of life in extreme Earth environments to the search for life away from Earth?
A: Some organisms on Earth have capabilities that stretch our wildest imagination. An essential part of astrobiology is exploring the limits of life to help us appreciate what's possible. Who would have thought that there are microbes that can reproduce at minus 15 degrees Celsius in salty water or up to 122 degrees Celsius on the seafloor? Who would have imagined microbes that thrive in extremely acid or alkaline conditions, below a pH of zero and up to a pH of 12? The oceans that exist beneath the surfaces of icy moons in the outer solar system will have very high pressure at depth and they could be highly acid or alkaline.
Q: Do you think it is likely that life – at least complex life – elsewhere would be along the lines of life as we know it?
A: We have to distinguish between science fiction and fact. We know from the spectra of light coming from the most distant stars that the same laws of physics apply throughout the observable universe, and extraterrestrial life will be constrained by those laws. To be alive requires a genome, which is chemically complex even in the simplest organism. There's only one set of chemical elements—the periodic table—and we know that certain elements have special properties. For this reason, only chemistry that is based on carbon can build extraterrestrial creatures as large and complex as us because carbon-based molecules can be huge, complicated, and diverse. I also would say it is highly likely that animal-like life elsewhere would use oxygen because oxygen is so unique in its properties. Conditions for truly complex life might be fairly specialized, as they are on Earth.
Q: By its nature, astrobiology seems to be highly interdisciplinary. Do you see this concept being applied to other fields?
A: Astrobiology is built around trying to address key scientific questions that are still unanswered. Planetary science and geology are necessary to appreciate the type of environment that hosted the origin of life, but you also need to know a great deal about biology and chemistry. I see other efforts that employ several disciplines to answer big questions, including the expected extent of global warming and how humankind should deal with it. Answering this question involves understanding the atmosphere, ocean, and the response of the biosphere and polar ice caps. But the issue goes beyond science into legal, economic and political realms.
Luckily astrobiology doesn't intersect politics too much.