When astronomer Percival Lowell looked through his telescope in northern Arizona in 1895, he was convinced that Mars was covered with a network of canals. Lowell published three books on the features of the Red Planet that he believed formed an elaborate system of transporting water from the polar ice caps. The canals, he theorized, where the work of a race of Martians desperately trying to cope with a drying world.
While Lowell’s ideas fuelled science fiction more than science, the concept of water on Mars isn’t such a farfetched concept.
In 2008, the Mars Reconnaissance Orbiter used radar to detect large fields of water ice just below the planet’s rocky surface in the Hellas Basin, located in Mars’ southern hemisphere. Since any exposed water ice on Mars would quickly vaporize, these underground ice fields may be all that’s left of a massive ice sheets that once covered several portions of the planet’s surface a few hundreds of millions of years ago—relatively recently, granted that Mars is more than four billion years old. One of the many features researchers examined is three times the size of Los Angeles and up to a half-mile thick, according to John W. Holt, a scientist from the University of Texas at Austin and the lead author of a 2008 paper in the journal Science.
The MRO’s HiRISE camera photographed several geological features that also point to the presence of glaciers, such as geological lines on the planet’s surface and features known as lobate debris aprons, or piles of rocks found at the base of cliffs. Moving glaciers are the most accepted source of these rock deposits. The glaciers sometimes left tongue-shaped patterns on the surface, evidence that they flowed down mountainsides.
When it touched down in 2008, the Phoenix Mars lander was the first probe to reach an area near the icy polar regions (which consist of frozen carbon dioxide, not water). Experiments conducted by the Phoenix showed that water ice did indeed exist just below the surface.
Mars can be located in the night sky this summer, with the handle of the Big Dipper pointing right towards it. The website EarthSky has a handy guide for finding the Red Planet in the late summer sky as well as the four other visible planets.