New Discovery: There Is Water In Planet Mars!

THERE is definitely water on Mars. That much has been known for years. The trouble is that most of it is ice, either buried beneath the surface, frozen in the depths of craters, or else locked up in ice caps at the planet's poles. What has intrigued astronomers recently is whether there might be liquid water on the surface.

At first glance, it seems unlikely: Mars is cold (the average temperature is around -60°C; only rarely does it venture into positive territory) and has a very thin atmosphere, with surface pressures well over a hundred times lower than those on Earth. Nevertheless, there have been occasional slivers of suggestive evidence, such as the supposed presence of briny droplets on the legs of the Mars Phoenix Lander, a NASA probe, which also discovered perchlorate, a chemical which can lower the freezing point of water, in the Martian soil.

On August 4th, though, NASA announced the strongest evidence yet for the existence of liquid water on the surface. A camera on the Mars Reconnaissance Orbiter, another NASA spacecraft, found dark streaks on a few comparatively warm, equator-facing Martian slopes. The streaks—a few meters wide and hundreds of meters long (see picture)—appear in the late Martian spring and disappear by late autumn. The best explanation, NASA reckons, is that the streaks are the result of flowing, briny water, with about the same salinity as Earth's oceans (which have a freezing point well below 0°C).

The streaks are not dark because they are wet, though, says NASA, but for some other reason. Perhaps the flow of water rearranges dirt particles on the surface, or maybe the streaks are the residue left behind when the briny water evaporates. And Mars-watchers are still puzzled as to why the streaks brighten again during the Martian winter. So the photographs are not absolutely definitive evidence of liquid water flowing on Mars—but they are the closest thing yet.



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