When we think "ancient Mars," we often picture roaring rivers, warm oceans, and if we're being optimistic, perhaps some simple life forms. But it's also possible the Mars of eons past was not a water-covered paradise at all. It may, in fact, have resembled a giant, dirty snowball.
That's a notion favoured by a forthcoming study in the American Geophysical Union's Journal of Geophysical Research. Examining two different climate modelling scenarios, the study's authors conclude that an ice-covered Mars better explains the peaks, valleys and channels crisscrossing the barren surface of the Red Planet today.
Three to four billion years ago, Mars was a very different world. Geomorphic features on present day Mars indicate an active water cycle with rivers and floods, and a recent analysis of trace water vapour in the atmosphere suggests an ancient ocean once blanketed much of the surface. But while it's almost certain that Mars used to be warmer, whether the planet's temperature hovered around that liquid water sweet spot is unclear. Since we can't go back in time, and the amount of field work we can do without putting boots on the ground is limited, scientists rely on models to piece together the Red Planet's climactic history as best they can.
In the new study, researchers constructed two different 3D climate models to examine the ancient Martian water cycle: One that treats Mars as a warm, wet planet with an average surface temperature of 50 ºF, another that makes Mars a snowball world roughly a hundred degrees colder. Turns out the cold model — while not perfect — produced more of the surface topography we see on Mars today, with ice patches roughly corresponding to modern valley networks. Transient warm periods, perhaps caused by meteor impacts or volcanic eruptions, could have melted these ice sheets and helped carve out the surface over time.
It's an intriguing possibility, but, the researchers acknowledge, a far cry from proving what ancient Mars looked like. We may never be entirely sure.
Still, if the new models are steering us right, they could have fascinating implications for the possibility of ancient Martian life. Biologists often look to extreme environments such as Antarctica for examples of life forms that could persist on a more hostile world, say, the icy moons Europa or Enceladus. Just maybe, these same cold-loving bugs offer us a window into the Solar System's oldest biology, as well.
Top image: Robin D. Wordsworth /AGU