In recent years, the question of Mars has shifted from whether it hosts advanced life (an idea shown to be futile) to whether it hosts water. Throughout the late 1800s, scientists such as William Whewell and Percival Lowell used observations with the best telescopes to argue that the Red Planet harbors a vast system of land and seas, as well as canals and intelligent life-forms that built them. Of course, skeptics like Edward Maunder and E. M. Antoniadi ultimately laid the scientific groundwork that dismantled the idea that Mars was inhabited by intelligent life. Now the conversation focuses more on the existence of water on Mars—and what that possibility could mean for humans, and Christians especially, on Earth.
A History of Hope for Water on Mars
A paper, published in 2000, hailed the discovery of recently formed gullies on Mars.1 The study caused a lot of excitement because it proposed that flowing liquid water formed the gullies. The terrain surrounding the gullies also gave strong evidence that they were recent formations (somewhere between one day and a couple million years ago). One scientist even commented that this discovery was "the smoking gun that says there's liquid water and Mars has all the requirements for life." Others expressed more reservations, thinking that some alternative process formed the gullies without help from liquid water. Research carried out since the discovery of the gullies seems to favor those alternative models.
Though the Martian gullies appeared similar to those on Earth (which usually are formed by liquid water), detailed studies ultimately showed that gullies on Mars do not mean that liquid water ever existed there. Further investigations revealed that the Martian gullies formed under conditions far too cold for liquid water to exist. Instead, thin layers of dry ice (frozen carbon dioxide) often blanket the regions where gullies form. A recently published paper shows that dry ice will fill pores below the ice layer. During seasons of warming or lower pressure, the dry ice will sublimate, causing the rocky surface layer on Mars to become unstable. In areas with steep inclines, the destabilized surface will give way, creating the gullies seen in satellite images.2
However, other observations provide more conclusive evidence for liquid water in Mars' past. As one example, over the past decade rovers and satellites have detected concentrated silica (SiO2) deposits in soils and bedrock,3 valley floors and plains,4 and in volcanic craters.5 (And scientists are still finding silica deposits with concentrations greater than 90 percent!) While numerous mechanical processes can form gullies, only a few options exist for the chemical processes required to form highly pure silica deposits and all of the best candidates include liquid water.
Realizing that Water Does Not Equal Habitability
As astronomers catalog more and more exoplanets, the search for evidence of water on Mars highlights a couple apologetics points to keep in mind. We should not be surprised that some (or even many) exoplanets seem to share Earth's large-scale features (size, density, distance from star, etc.), including the presence of liquid water. After all, water is one of the most abundant molecules in the universe. However, we should also be cautious about assuming that such similarities mean that an exoplanet also matches Earth's capacity to support life. As our investigations continue to show, the environment on Mars poses hostility to life—even though the Red Planet shares many physical features in common with Earth.