Elevation changes also indicate where Mars may have once had a vast northern ocean.
Mars Orbiter Laser Altimeter Science Team/NASA

Three and a half billion years ago, an asteroid slammed into Mars. The cataclysm wasn’t terribly unusual for this period in the solar system’s history, but the fallout would leave its mark. The asteroid carved out an enormous crater. It also sent a wall of water a thousand feet high hurtling around the young Red Planet, which was much more blue at the time.

That wave then slammed into land, creating strange landforms on Mars. Since 2017, Francois Costard, a scientist at the French National Centre for Scientific Research, has been advocating this theory to explain a region called the Thumbprint Terrain, and now he thinks he may have found the crater that was ground zero for the tsunami. He published his findings June 26 in the Journal of Geophysical Research Planets.

via GIPHY

Long ago on Mars, water carved deep riverbeds into the planet’s surface—but we still don’t know what kind of weather fed them. Scientists aren’t sure, because their understanding of the Martian climate billions of years ago remains incomplete.

A new study by University of Chicago scientists catalogued these rivers to conclude that significant river runoff persisted on Mars later into its history than previously thought. According to the study, published March 27 in Science Advances, the runoff was intense—rivers on Mars were wider than those on Earth today—and occurred at hundreds of locations on the red planet.

But it’s a puzzle why ancient Mars had liquid water. Mars has an extremely thin atmosphere today, and early in the planet’s history, it was also only receiving a third of the sunlight of present-day Earth, which shouldn’t be enough heat to maintain liquid water. “Indeed, even on ancient Mars, when it was wet enough for rivers some of the time, the rest of the data looks like Mars was extremely cold and dry most of the time,” Kite said.

Seeking a better understanding of Martian precipitation, Kite and his colleagues analyzed photographs and elevation models for more than 200 ancient Martian riverbeds spanning over a billion years. These riverbeds are a rich source of clues about the water running through them and the climate that produced it. For example, the width and steepness of the riverbeds and the size of the gravel tell scientists about the force of the water flow, and the quantity of the gravel constrains the volume of water coming through.

Their analysis shows clear evidence for persistent, strong runoff that occurred well into the last stage of the wet climate, Kite said.