Mars may be incredibly dry and dusty today, but evidence continues to pile up that it was once a very watery world. Now the Curiosity rover has found signs of an ancient flood of biblical proportions, most likely kicked off by a climate-changing asteroid impact.
Apart from a few super salty underground lakes, modern Mars is a global desert. But that wasn’t always the case – decades of observations by orbiters in the sky and rovers on the surface have revealed the dried-up remains of rivers, lakes and even oceans. Those structures may paint a peaceful picture of early Mars but a new study reveals a land still scarred by water at its wildest.
Over the past eight years, the Curiosity rover has been exploring a location known as Gale crater, and slowly climbing its central peak called Mount Sharp. It became apparent pretty quickly that the crater used to be a lake that periodically filled and drained over tens of millions of years. But now it seems one refill was far more intense than the others.
In the new study, researchers from Jackson State University, Cornell, the Jet Propulsion Laboratory and the University of Hawaii identified sediment structures in Gale crater indicating that megafloods occurred there around 4 billion years ago. A series of symmetrical gravel ridges each standing 10 m (32.8 ft) high appear to be “antidunes” – sediment structures that, here on Earth, form under very fast-flowing water.
By measuring the distance between the crest of each ridge, the team was able to estimate that they were created by flood waters at least 24 m (78.7 ft) deep and traveling at upwards of 10 m (32.8 ft) per second.
“We identified megafloods for the first time using detailed sedimentological data observed by the rover Curiosity,” says Alberto G. Fairén, co-author of the study. “Deposits left behind by megafloods had not been previously identified with orbiter data.”
So what could have caused such extreme flooding? The researchers believe that the most likely explanation is a huge impact by an asteroid, which would have melted a sizeable segment of the ice that covered Mars at the time. That would have released huge amounts of water vapor, carbon dioxide and methane into the atmosphere, temporarily changing the climate into a warmer, wetter world.
Torrential rain would have followed in this scenario, which would then have rushed down the sides of Gale crater and the slopes of Mount Sharp to produce flash floods in the lower-lying regions.
“Early Mars was an extremely active planet from a geological point of view,” says Fairén. “The planet had the conditions needed to support the presence of liquid water on the surface – and on Earth, where there’s water, there’s life. So early Mars was a habitable planet. Was it inhabited? That’s a question that the next rover Perseverance will help to answer.”
The research was published in the journal Scientific Reports.
Source: Cornell University
