NASA's Mars Reconnaissance Orbiter shows gullies near the edge of Hale crater on southern Mars.
Credit: NASA
WASHINGTON, D.C.: Changes in gullies on Mars suggest that there is flowing water on the red planet, scientists said.
Martian gullies carved into hill slopes and the walls of impact craters were discovered several years ago. On Earth, gullies usually form through the action of liquid water – long thought to be absent on the Martian surface because the temperature and atmospheric pressure were believed to be too low.
But direct observation tells a different story, according to research published in Geophysical Research Letters released by the American Geophysical Union.
Melting of small amounts of ice
Using high resolution imaging to look at the planet's surface, Dennis Reiss, a geologist at Westfaelische Wilhelms University in Muenster, Germany and his team of researchers, observed that from November of 2006 to May of 2009, a two-meter-wide gully had grown in length by 50 meters in one year and by 120 meters the following year.
"There has been a long debate about what has caused them," said Harold Hiesinger, a geologist at Westfaelische Wilhelms University and a member of Reiss's team.
Though they believe that these changes are best explained by a process of erosion triggered by the melting of small amounts of ice.
Carbon dioxide common explanation
Other researchers argue that such changes could be explained by the presence of carbon dioxide.
"I agree with these authors, and others, that carbon dioxide is very unlikely to be responsible for gullies," said Michael Manga, a geologist at the University of California, Berkeley in an email, explaining that CO2 is a gas and would cause explosions:
"It wouldn't stick with the particles and allow them to keep flowing," he said.
Dry avalanches or wet landslides?
There has been debate on whether water is necessary to create such gullies and some argue that they could've been made by small, dry avalanches.
"But the gullies have levees (ridges) around them and this is characteristic of wet landslides on Earth," Manga said.
