The fog of discovery

According to a report at Space.com, two NASA researchers are making a strong case that microbial life exists today benath the Martian surface. The evidence is indirect, and seems to include three major threads. First, the European Mars Express orbiter, along with ground-based telescopes, have detected fluctuating levels of methane in the Martian atmosphere. Second, the two researchers have finished a study of an analogue subsurface ecosystem in Spain, and their findings indicate that similar places beneath the Martian surface should be able to support life as well. Finally, the U.S. Opportunity rover made observations of minerals (such as jarosite) that confirm the geological similarities with sites like the one in Spain. This is, at least, my admittedly inexpert interpretation of the report.

When I first heard about the methane observations a while back, I thought they were pretty amazing. I could not figure out why people were not making a bigger deal out of the story. In fact it is hard to imagine another possible methane source besides living organisms like terrestrial methanogenic bacteria. (On the other hand, our failure of imagination is no proof that Mars has not thought up an alternate, wholly non-biological process to produce it!)

So, is there life on Mars? It is maddeningly hard to say, even now! I had always imagined that if life did indeed exist there, then there would be a particular moment, a revelation, a "Eureka!" But maybe it won't happen that way at all. Maybe we will later realize that we've been seeing the growing evidence for years:

• The still-perplexing (to me, anyway) Labeled Release experiment results from the Viking landers in 1976;
  
• The controversial microscopic and chemical evidence from Martian meteorite ALH 84001;
  
• The increasingly understood history of flowing and standing water on the ancient Martian surface;
  
• And now the queerly variable methane content of the present-day atmosphere.

One day, all of these may be remembered in retrospect as the chapters of a single exciting story. But not yet, alas. We are too close to see the shape of that story, or to determine which pieces of evidence are most crucial, or to guess the significance that it will bear. For a while yet we will struggle along, stumbling through the fog of discovery.