Decoding the Red Planet

As we saw in the last chapter, Mars seems dead to the orbiters that daily send back images of the surface. The atmosphere is tenuous, ultraviolet radiation and cosmic rays scorch the soil, and it rarely gets above freezing even on the balmiest summer day.15 It’s un­likely any form of life could exist on the surface now, but Mars has not always been so inhospitable. NASA’s strategy in searching for life in the Solar System is to “follow the water,” and even if there’s no surface water now, there was in the past. Each of the Mars Ex­ploration Rovers, Spirit and Opportunity, was designed for just a ninety-day mission. In the end, they have vastly exceeded expecta­tions with their indomitable traverses of the forbidding Martian terrain. Think of them as twin robotic field geologists whose pri­mary goal is to search for the signposts of water.16 The record of past water can be found in the rocks, minerals, and landforms on Mars, particularly those that could only have formed in the pres­ence of water.

Spirit and Opportunity were not designed to detect current or past life in the Martian soil,17 but they can do the detective work needed to say whether there have been stable bodies of water that could have supported life in the past. Surface rocks reveal evidence of previous water in the way that they formed, by processes like precipitation, evaporation, and sedimentation. They can also hold clues for the possibility that water currently exists under the sur­face. The rovers have helped scientists diagnose the history of the Martian climate, which is now thought to have been warmer and wetter 2-3 billion years ago. The twin robots are also trying to parse the different contributions of wind, water, plate tectonics, volcanism, and cratering to the sculpting of the surface. Spirit and Opportunity provide “ground truth” data for calibrating the or – biters that continue to do remote geology and scout for future landing sites. A final goal is to prepare the stage for future as­tronauts by understanding the unique challenges of the Martian environment.