Categories: Mars

Mars Gullies From Snow and Ice Melt “Relatively Recent”

[/caption]
A new study of gullies seen on Mars provides evidence that water flowed recently on the Red Planet, at least in geologic terms. Planetary geologists at Brown University have found a gully fan system on Mars that formed only about 1.25 million years ago. The structure of this fan offers compelling evidence that it was formed by melt water that originated in nearby snow and ice deposits. This time frame may be the most recent period when water flowed on the planet. This most recent finding comes on the heels of discoveries of water-bearing minerals such as opals and carbonates, and together all these discoveries provide clues that Mars was, at least occasionally, wetter and warmer for far longer than previously thought.

While gullies are known to be young surface features, it’s difficult to date them. But the Brown scientists were able to date the gully system because of craters in the area, and also hypothesize what water was doing there.

The gully system shows four intervals where water-borne sediments were carried down the steep slopes of nearby alcoves and deposited in alluvial fans, said Samuel Schon, a Brown graduate student and the paper’s lead author.

“You never end up with a pond that you can put goldfish in,” Schon said, “but you have transient melt water. You had ice that typically sublimates. But in these instances it melted, transported, and deposited sediment in the fan. It didn’t last long, but it happened.”

The gully system shows four distinct lobes. Credit: NASA/JPL/University of Arizona

The gully system is located on the inside of a crater in Promethei Terra, an area of cratered highlands in the southern mid-latitudes. The eastern and western channels of the gully each run less than a kilometer from their alcove sources to the fan deposit.

Viewed from afar, the fan appears as one entity several hundred meters wide. But by zooming in with the HiRISE camera aboard the Mars Reconnaissance Orbiter, Schon was able to distinguish four individual lobes in the fan, and determine that each lobe was deposited separately. Moreover, Schon was able to identify the oldest lobe, because it was pockmarked with small craters, while the other lobes were unblemished, meaning they had to be younger.

Next came the task of trying to date the secondary craters in the fan. Schon linked the craters on the oldest lobe to a rayed crater more than 80 kilometers to the southwest. Using well-established techniques, Schon dated the rayed crater at about 1.25 million years, and so established a maximum age for the younger, superimposed lobes of the fan.

The team determined that ice and snow deposits formed in the alcoves at a time when Mars had a high obliquity (its most recent ice age) and ice was accumulating in the mid-latitude regions. Sometime around a half-million years ago, the planet’s obliquity changed, and the ice in the mid-latitudes began to melt or, in most instances, changed directly to vapor. Mars has been in a low-obliquity cycle ever since, which explains why no exposed ice has been found beyond the poles.

The team tested other theories of what the water may have been doing in the gully system. The scientists ruled out groundwater bubbling to the surface, Schon said, because it seemed unlikely to have occurred multiple times in the planet’s recent history. They also don’t think the gullies were formed by dry mass wasting, a process by which a slope fails as in a rockslide. The best explanation, Schon said, was the melting of snow and ice deposits that created “modest” flows and formed the fan.

The team’s findings appear in the March issue of Geology.

Source: Brown University

Nancy Atkinson

Nancy has been with Universe Today since 2004, and has published over 6,000 articles on space exploration, astronomy, science and technology. She is the author of two books: "Eight Years to the Moon: the History of the Apollo Missions," (2019) which shares the stories of 60 engineers and scientists who worked behind the scenes to make landing on the Moon possible; and "Incredible Stories from Space: A Behind-the-Scenes Look at the Missions Changing Our View of the Cosmos" (2016) tells the stories of those who work on NASA's robotic missions to explore the Solar System and beyond. Follow Nancy on Twitter at https://twitter.com/Nancy_A and and Instagram at and https://www.instagram.com/nancyatkinson_ut/

Recent Posts

Astronomers Find a 3 Million Year Old Planet

Astronomers have just found one of the youngest planets ever. At only 3 million years…

9 hours ago

There was Hot Water on Mars 4.45 Billion Years Ago

Mars formed 4.5 billion years ago, roughly the same time as the Earth. We know…

13 hours ago

Axion Dark Matter May Make Spacetime Ring

Dark matter made out of axions may have the power to make space-time ring like…

17 hours ago

Earth’s Old Trees Keep A Record of Powerful Solar Storms

Most of the time the Sun is pretty well-mannered, but occasionally it's downright unruly. It…

1 day ago

New Supercomputer Simulation Explains How Mars Got Its Moons

One mystery in planetary science is a satisfying origin story for Mars's moons, Phobos and…

2 days ago

The Early Universe May Have Had Giant Batteries of Dust

The largest magnetic fields in the universe may have found themselves charged up when the…

2 days ago