Literature

Astrobiology is a scientific enigma, because there are no examples of extraterrestrial life on which to build a body of knowledge. It has life on Earth as a clear reference point, but beyond Earth, everything examined has proved barren. In The Living Cosmos, author Chris Impey provides an overview of current thinking in astrobiology, but it consists essentially of discussing how and where we should be looking for extraterrestrial life.
A positive review of the book is by Bruce Jakosky, who presents astrobiology as "firmly science-based rather than speculative". Planet Earth provides the foundation for the science: "We know how life functions, how it may have originated and some types of environment that support its existence." Many things are packaged up together here, and this is a danger. In particular, the claim that we know how life "may have originated" is way off the mark. There have been many hypotheses and much testing of hypotheses, but none of it encourages us to think that we know how life may have originated on Earth. The field is full of controversy and over-optimistic claims. For examples, go here and here.

Beyond the Earth, the most promising planet for hosting life in our Solar System is Mars, and this is where there has been intensive effort by astrobiologists. "Mars is arguably the best place to look for present or past life, given the evidence for liquid water there and the planet's proximity to Earth." However, in his review, Jakosky majors on the need for future missions rather than reflect on what has been learned so far. This is the major problem that we have with astrobiology: it is unable to consider the possibility that the sought-after life is not there! According to the adherents, life beyond Earth must exist, and our task is to keep searching until we find it!

"Even the toughest micro-organisms would have been unable to survive in the harsh environment, say scientists" (Source - go here)

Our understanding of Mars is rapidly developing. Signs of water in the Martian past are plentiful, and this has raised expectations. But today, a report has been published about sand flume studies of delta formation. These have shown that a stepped delta structure found on Mars can best be modelled by a "sudden release of water from subsurface storage". "The distinct morphology of martian stepped (terraced) deltas could only have originated from a single basin-filling event on a timescale of tens of years." This report raises questions about how long water bodies occupied the Martian surface.

Also this week, comments have been made about the extreme salinities of water bodies when they existed on Mars. Researchers have effectively thrown up their hands in despair: "That's not a very good place to live, and it's a worse place for the kind of chemistry that we think gave rise to life on Earth". "At first, we focused on acidity, because the environment would have been very acidic. Now, we also appreciate the high salinity. This tightens the noose on the possibility of life." But they are not giving up. There is always something more to explore: "The best hopes for a story of life on Mars are at environments we haven't studied yet". (This research is now published: Toska et al, 2008)

Astrobiologists want access to every conceivable habitat.

"Beyond Mars, several moons in the outer Solar System are worth exploring. Jupiter's satellites Europa, Ganymede and Callisto are good targets because they may have recently hosted liquid water. Saturn's moons Titan and Enceladus, targets of the ongoing Cassini mission, are of great interest because of the abundance of organic molecules (especially on Titan) and the potential for near-surface liquid water (Enceladus). NASA is studying possible missions to these objects as a prelude to a major push mission into the outer Solar System."

The question needs to be asked: what makes this science? There are no hypotheses being tested. There is no hint that astrobiologists are willing to consider that their basic assumption (about extraterrestrial life existing) can ever be falsified. There is no acknowledgement that all the research to date emphasises the uniqueness of Earth as an environment supporting life. The insatiable appetite for the next probe is not grounded in reality, but in aspiration. The hype surrounding the quest for extraterrestrial life springs from an ideology that appears to use science as a tool to achieve its goals.

Quest for extraterrestrial life
Bruce Jakosky
Nature, 451, 890 (21 February 2008) | doi:10.1038/451890a

BOOK REVIEWED - The Living Cosmos: Our Search for Life in the Universe by Chris Impey, Random House: 2007.
First paragraph: From only one example, that of life on Earth, we have learned a lot about what makes a planet habitable. We know how life functions, how it may have originated and some types of environment that support its existence. Yet we do not know how widespread life might be. To do so we must extend our knowledge past Earth, into the Solar System and beyond.

See also:

Tosca, N.J., Knoll, A.H. and McLennan, S.M. Water Activity and the Challenge for Life on Early Mars. Science 320, 30 May 2008: 1204-1207 | doi: 10.1126/science.1155432