Searching for life beyond our planet: Are we there yet?

Abstract

It has been 35 years since NASA undertook a bold journey, to search for life on another planet, by sending the Viking landers (Figure 1) to the surface of Mars. The general consensus was that both landers failed to find conclusive evidence of extant Martian organisms. NASA started the journey with the best car on the market, with the transmission in high gear, but after hitting a big bump in the road, it decided to downshift and take a closer look at the map. Subsequent studies focused on characterizing the physical, chemical, and geological environment on Mars today and in the past, before any more bold attempts were made to directly search for life. This led to an unanticipated but necessary detour that has provided us with some of the best highlights of the journey so far. Examples are the discovery of widespread secondary minerals that formed in the presence of liquid water, the detection of ground ice in the high latitudes of both hemispheres, including the polar caps, and the direct analysis of ground ice by the Phoenix mission in 2008. These research efforts have also allowed us to vastly improve the tools we now have at our disposal. But let there be no mistake: This detour was a necessary course of action, because it was futile to search for life on Mars without understanding the Martian environment.