Even though orbiters have eyed it from space and landers have rumbled across its surface, Mars still has more secrets to reveal. Two findings emerged this week: the possibility of an active glacier far from the planet's poles and evidence that sulfur--not carbon--was the element driving the planet's warmer climate long ago. Both discoveries could force some rethinking about martian evolution and dynamics--and maybe even provide insights about Earth's past.
The glacier discovery was announced Wednesday by the European Space Agency (ESA). A high-resolution stereo camera aboard ESA's Mars Express spacecraft spotted the feature in a region called Deuteronilus Mensae, located in the mid-north latitudes of the planet. The Mars Express science team drew the preliminary conclusion that the material in the feature is water ice and that it accumulated as recently as 10,000 years ago, probably from an underground source. Other deposits of water ice have been mapped at the martian poles, but they're much bigger and are millions of years old. The find is a surprise because the prevailing view is that any water reaching the martian surface from underground quickly evaporates and eventually drifts into space. Yet all of the physical characteristics of the feature are "consistent with that of a glacier," says geologist and team member Ronald Greeley of Arizona State University in Tempe.
Meanwhile, in the 21 December issue of Science, a team from Harvard University and the Massachusetts Institute of Technology offers a possible solution for the curious absence of carbon-based minerals on Mars. A buildup of carbon dioxide in the ancient martian atmosphere supposedly produced enough of a greenhouse effect to allow liquid water to flow for a time on the surface. The problem is that such a process should have deposited ample carbon-containing minerals on the planet's surface--something that hasn't been found. So the researchers have come up with a new explanation: Large amounts of sulfur dioxide (SO2) in the atmosphere, the result of early volcanic activity, captured enough heat to allow water to flow. This would explain the plentiful distribution of sulfates among martian minerals, as sulfur dioxide fell out of the atmosphere and mixed with the wet surface.
The research suggests that "it is possible to build up enough atmospheric SO2 to help warm early Mars," says planetary geochemist and lead author Itay Halevy of Harvard. This revelation, he notes, also "might imply that SO2 played a more important role in Earth's history than previously thought."
Planetary geologist Alfred McEwen of the University of Arizona in Tucson, who is principal investigator for the HiRISE camera aboard NASA's Mars Reconnaissance Orbiter, says the potential glacier is intriguing enough that MRO should also image Deuteronilus Mensae and train the spacecraft's spectrometer on the site to scan for water ice. He cautions, however, that other, similar martian features have turned out to be made of indurated dust, which resembles ice in orbital images.