Exobiology: The Search for Life on Mars

Exobiologists seek to understand how life originated on Earth by studying chemical and physical conditions elsewhere in our solar system and our galaxy. The origin of life on Earth is not well understood but was evidently based on chemical evolution from simple compounds present on the newly formed planet to create a system of replicating organic chemicals. Unfortunately, it is difficult to study early Earth directly because the earliest geological formations have been largely erased by erosion and deposition. In contrast, on Mars we can still see the early crust in the form of heavily cratered highlands. Major exobiology goals for Mars are to

1. Determine whether life presently exists on Mars or, as is thought more likely, has existed in the past
2. Define the nature of early martian environments and understand differences from the early environments of Earth
3. Determine the history of the biogenic elements (Carbon, Hydrogen, Nitrogen, Oxygen, Sulphur, Phosphorus) on Mars and of organic chemistry there (that is, the chemistry of carbon bearing compounds whether biologic or abiologic in origin)

In order to achieve these goals, Mars exploration spacecraft will visit sites where we may expect to find sedimentary rocks containing evidence of biologically-important minerals (such as carbonates, sulfates, phosphates) and preserved organic compounds. (Note that organic molecules are rapidly destroyed at the surface of Mars today by the intense ultraviolet light from the Sun -- light that, on Earth, is filtered out by our ozone layer). Mars exploration may even lead to the discovery of a fossil record of past microbial life.