Tomorrow (2nd December) at 2pm EST NASA will hold a press conference “to discuss an astrobiology finding that will impact the search for evidence of extraterrestrial life” This sounds fairly exciting and of course it’s an invitation to science bloggers to speculate about what they might have discovered. At a previous press conference in 1996 NASA announced that it had found bacteria-like structures in a meteorite that had come to Earth from Mars. Could tomorrow’s announcement be something similar?
The only clue we get is a list of scientists who will attend the press conference and who are probably the authors of a paper to be published in Science on the discovery, whatever it is. Here is a brief summary of their profiles
- Mary Voytek: A microbiologist interested in aquatic microbial ecology and biogeochemistry. She has studies life in extreme conditions on Earth suxh as deep-sea hydrothermal vents and terrestrial deep-subsurface sites and is an Interim Senior Scientist for Astrobiology in the Science Mission Directorate at NASA HQ.
- Felisa Wolfe-Simon:a NASA Astrobiology Research Fellow through the NAI and Exobiology at NASA. She has studied (hypothetical) life forms with unusual chemistry including arsenic-based life.
- Pamela Conrad: Works at NASA’s Virtual Planetary Laboratory and studies signatures for life and planetary habitability assessment.
- Steven Benner: A biochemist who runs a laboratory that aims to create artificial life. The lab also studies bio-signatures from planets other than Earth and is working with NASA to deign the next generation of probes to Mars
- James Elser: A researcher in the field of biological stoichiometry, the study of balance of energy and multiple chemical elements in living systems. Currently, he is an active member of the ASU’s NASA-funded Astrobiology project “Follow the Elements”
So what do we think this is about? The intriguing possibility is that the team has indeed found some biological signature indicating the possibility of extraterrestrial life. It could be something as simple as oxygen or an amino acid. This could be an observation from a probe looking at a planet or moon in the solar system such as Mars, Titan, Europa or Rhea. Alternatively it could be from another metiorite found on Earth, or a comet. A discovery related to exoplanet searches is also possible but does not seem to be such a good fit.
Of course it is also possible that the discovery is something less extraterrestrial, such as an unusual life-form found on Earth. It is not likely to be the discovery of a radio signal from extraterrestrials because the expert profiles are wrong, but who knows?
Update (2-Dec-2010): The announcement turns out to be that the scientists have taken a microbe from the arsenic rich waters of lake Como and put it in a soup which is rich in arsenic and low in phosphorus.
Arsenic is highly poisonous to us because it is chemically similar to phosphorus and replaces phosphorus in the molecules in our body, but it is not close enough for this to work. However, what was found was that there is one bacteria from the lake that takes in the arsenic and continues to live and subdivide. In particular the phosphorus in the DNA of the bacteria gets replaced with arsenic.
This is interesting because it means that DNA based extraterrestrial life might evolve in environments that don’t have phosphorus.
Some websites are still reporting that they have discovered a completely new type of lifeform that uses arsenic instead of phosphorus. This is not quite the situation. Instead it is a conventional microbe with a remarkable ability to use arsenic instead of phosphorus when necessary.
Update (3-Dec-2010): There was an interesting moment in the press conference when Benner tried to explain why he is so sceptical about this discovery. He said that phosphor gets incorporated into life’s molecules through a complex sequence of 14 enzyme catalysed reactions. Although arsenic is chemically similar to Phosphorus, it is not so similar that it could substitute into such a reaction sequence, therefore it is hard to see how it could get into DNA.
Wolfe-Simon came back with a simple response. While phosphor based chemicals are hard to produce, their arsenic based counterparts form spontaneously in a testtube when you mix the chemicals together!
Of course this does not completely answer the objection, it is still hard to see how an alternative chemical pathway can exist inside these bacteria, but if Wolfe-Simon has done her work well, that is exactly what is happening.
If we speculate a little beyond what was said the implication for the formation of life both on Earth and extraterrestrial is startling. It is one of the great puzzles of science that basic life arose spontaneously from the primordial soup on Earth. If the chemical reactions that life uses are so complex how could they have arisen naturally?
Suppose the Lake Como bacteria is not just a remarkable micro-organism that has adapted to an arsenic based environment. Could it be a throw-back to an earlier form of life that evolved from scratch in a chemical soup where the molecules for life could form spontaneously using arsenic instead of phosphor?
Arsenic based molecules are less stable than their phosphorus equivalents, so if an arsenic based micro-organism could adapt to using phosphorus it would be able to make the leap to water dominated environments where evolution can progress. So the Como Lake bacteria may not be phosphorus based life that adapted to arsenic at all. It could be arsenic based life that adapted to use phosphorus, but unlike other more evolved cells, it retains the mechanisms needed to live off arsenic.