The region shows the common features of a fluvial valley, like many other regions on the surface of Mars. The weird thing about Lyot is its age. It is estimated to be between 1.5 and 3 billion years old, so it formed when Mars was already a desert with no flowing water on its surface. The study is published in Geophysical Research Letters.
Its formation has been connected to a suddenly warm atmosphere that thawed ice deposits, although this has not been witnessed anywhere else. The region has a famous crater also named Lyot that's 225 kilometres (140 miles) in diameter. It's likely that the impact event that formed Lyot also jumpstarted the formation of the valley.
“Based on the likely location of ice deposits during this period of Mars’ history, and the amount of meltwater that could have been produced by Lyot ejecta landing on an ice sheet, we think this is the most plausible scenario for the formation of these valleys,” lead author David Weiss of Brown University said in a statement.
The team also looked at alternative scenarios that connected the asteroid to the formation of the valleys. The impact might have released a buried reservoir of water, which then moved outwards and carved the valleys. This is believed to be an unlikely scenario as there’s little supporting evidence for it.
“If these were formed by deep groundwater discharge, that water would have also flowed into the crater itself,” Weiss added. “We don’t see any evidence that there was water present inside the crater.”
Another possibility was rain. The impact must have vaporized a huge amount of ice and rock, which rained down afterward and could have carved the valleys we now observe. However, this hypothesis too seems unlikely. The valleys start far away from the crater, and they left the material ejected by the impact untouched.
“The vast majority of the valleys seem to emerge from beneath the ejecta on its outer periphery, which casts serious doubt on the rainwater scenario.”
A strong piece of evidence for the hot rock melting ice scenario is the lack of secondary craters. When a powerful impact happens, rocks will be thrown around and produce tiny craters near the main one. There’s a lot less around Lyot crater than one would expect. Based on that, the researchers estimate an ice cap between 20 and 300 meters (66 and 985 feet) thick.
Researchers are now considering if this mechanism could have also played a role much earlier in Mars' history when the Red Planet wasn’t that red.