Mars once had giant river beds bigger than anything on Earth

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In the river basins, for which there is most data, Mars' rivers were about two times wider than those on Earth.

Weighing in at no more than 4 pounds (1.8 kilograms), the helicopter is a technology demonstration project now going through the rigorous verification process certifying it for Mars.

The 2020 rover will conduct geological assessments of its landing site on Mars, determine the habitability of the environment, search for signs of ancient Martian life, and assess natural resources and hazards for future human explorers.

According to Dr Heggy and Dr Abotalib, cracks in Mars' numerous craters and deep underground pressure have helped water springs to well up to the surface. Remote sensing data has revealed numerous valleys which appear to be precipitation-fed former rivers.

This complicates the picture for scientists trying to model the ancient martian climate, said lead author Edwin Kite, Assistant Professor at the University of Chicago.

But, he said, the constraints could be useful in winnowing the many theories researchers have proposed to explain the climate. Pictured: In this handout image supplied by the European Space Agency (ESA) on July 16, 2008, The Echus Chasma, one of the largest water source regions on Mars, is pictured from ESA's Mars Express.

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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. And in 2012, NASA's Curiosity space rover sent back images of smooth, round pebbles from the bottom of one such riverbed, their lack of rough edges evidence that water had once flowed over them.

The results show that numerous rivers-most larger and wider than rivers found on Earth-still had a strong flow 3 billion years ago, well into the period when the planet had begun to dry up and even as recently as 1 billion years ago. 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 run-off that occurred well into the last stage of the wet climate", Kite said.

Scientists previously thought these features were affiliated with surface water flow or close subsurface water flow, says Heggy.

Kite said that this work implies that something in the current science of planets and the early solar system is wrong, because everything scientists know suggests that the rivers on Mars should have been small and temporary, if they existed at all. "The wettest day of the year is still very wet".

It's also possible the climate had a sort of "on/off" switch, which tipped back and forth between dry and wet cycles, Kite speculated. "However, this challenge is not met by most existing models of Mars' planetary climate evolution", the study said.

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