Mars Water May Have Come From Orographic Precipitation
July 24, 2013

Snow May Have Helped Carve Some Martian Valleys

redOrbit Staff & Wire Reports - Your Universe Online

Orographic precipitation, or rain and snow that falls when moist prevailing winds are forced upwards by mountain ridges, appears to have played a role in the formation of some Martian valleys, researchers from Brown University in Rhode Island report in a recently published study.

While the valley networks that cover the surface of the Red Planet provide strong evidence water once flowed on Mars, the source of that ancient water has been the cause of much debate amongst scientists. Some of them claim it originated from underground, while others assert it fell as precipitation.

The Brown University study, which has been accepted and published online by the journal Geophysical Research Letters, has revealed water-carved valleys at four different locations on Mars appear to have been caused by runoff from orographic precipitation.

Geological sciences graduate student Kat Scanlon and her colleagues claim their findings provide the most detailed evidence yet of an orographic effect on ancient Mars, and could provide new insight into what the climate and atmosphere was like during the planet's earliest days.

Scanlon had previously worked with the orographic effect while performing graduate work in meteorology in Hawaii, which is the location of such a pattern. In Hawaii, moist tropical winds from the east are pushed upwards when they hit the mountains of the big island.

Those winds do not possess enough kinetic energy to reach the summit, so they release their moisture on the eastern side of the island, turning a portion of it into a tropical jungle. On the other hand, the western side is nearly a desert because it rests in a rain shadow cast by the mountain peak, the researchers explained.

Scanlon believes similar orographic patterns could have been occurring on early Mars, and the valley networks could have been an indicator. Setting out to see if they were precipitation related, she and her colleagues first selected four areas where the valley networks were found along either tall mountain ridges or raised crater rims.

"To establish the direction of the prevailing winds at each location, the researchers used a newly developed general circulation model (GCM) for Mars," the university explained in a statement. "The model simulates air movement based on the gas composition scientists think was present in the early Mars atmosphere.

"Next, the team used a model of orographic precipitation to determine where, given the prevailing winds from the GCM, precipitation would be likely to fall in each of the study areas," they added. "Their simulations showed that precipitation would have been heaviest at the heads of the densest valley networks."

Scanlon said her team was able to confirm the drainage density in those locations varied in the same type of way that would be expected from "the complex response of precipitation to topography."

The atmospheric patterns used by the researchers in the GCM were based on a general circulation model that predicted a cold climate, and as such, snow was the type of precipitation modeled for the purposes of the study.

However, they note the snow could have been melted by episodic warming conditions in order to form the valleys, and some of the precipitation could have been rain the entire time.

According to Scanlon, "The next step is to do some snowmelt modeling. The question is how fast can you melt a giant snowbank. Do you need rain? Is it even possible to get enough discharge [to carve the valleys] with just the snowmelt?" With the information obtained from this study, answering those questions could provide valuable new insight into the climate that would have existed on Mars several billion years ago.