By Trent C. Stockton
June 15, 2001
Two University researchers in earth and planetary sciences in Arts & Sciences have suggested that western Arabia Terra, an area on Mars the size of Europe, experienced an extensive erosion event caused by flowing water.
"We argue that this entire region has been massively eroded," said Brian M. Hynek, a doctoral candidate in earth and planetary sciences who performed the study with Roger J. Phillips, Ph.D., professor of earth and planetary sciences and director of the University's McDonnell Center for the Space Sciences. "The region used to look like the rest of the highlands, but a vertical kilometer of material --enough to fill the Gulf of Mexico --has been relocated downslope and spread out into the northern plains."
The researchers used high-resolution topographic data from the Mars Orbiter Laser Altimeter (MOLA) instrument on the Mars Global Surveyor mission to construct detailed maps of the planet's surface.
"Before this mission, topography was known only within a kilometer at best," Hynek said. "Now we are accurate to within half a meter at any given point on the surface of Mars."
MOLA's accuracy and the more than half-billion data points it has collected reveal many previously unknown features of Mars' surface. The research was published in the May issue of the journal Geology.
Mars is divided into two main areas: the older Southern Highlands with lots of craters and valley networks, and the younger Northern Lowlands with few craters and no valley networks.
When the researchers began studying maps from the new data, they noticed that one region, western Arabia Terra, is a kilometer lower than the rest of the highlands. Before the Mars Global Surveyor mission, this region was lumped in with the rest of the highlands.
But the new topography reveals much more is going on there than previously thought. Looking carefully at western Arabia, the researchers noticed that it differs from the rest of the highlands in having very few large craters, only a few traces of valley networks and numerous erosional remnants.
"This combination makes it very likely that the entire region was swept away," Hynek said.
But how can you remove all this material and carry it away?
"Lots of things can erode planets," Hynek said. "Wind is very effective on long timescales. Volcanoes, ice and glaciers can all erode features, but on this large of a scale these are unlikely explanations."
He said that the massive size of the eroded area and the remnants of valley networks suggest running water was responsible.
The researchers believe the erosion event took place very early in Mars' history, during the Late Noachian, and ended around 3.5 billion to 3.8 billion years ago. The timing coincides with other water features on the planet and heavy outflow of lava from volcanoes early in Mars' history, as the researchers noted in the journal Science earlier this year.
Volcanic eruptions emit great amounts of water, carbon dioxide, sulfur and other greenhouse gases as well as lava and ash. This could have led to the development of an atmosphere on Mars that persisted for a few hundred-million years --long enough to raise surface temperature above freezing and maintain liquid water on the planet's surface.
The researchers are now focusing attention on a large outcrop of hematite within western Arabia Terra, the Terra Meridiani region. Hematite, an iron oxide, forms in the presence of water on Earth.
"This is very likely to be one of two Mars Rover landing sites in 2004," Hynek said. "We want to go where the water was."