The discovery that the Gale crater on Mars was once a lake is a significant plus to the theory that Mars once had a moist and warm atmosphere. Now it remains only to wait for the confirmation of this theory by computer models.
"The presence of lakes that have lasted for millions or even tens of millions of years means that the atmosphere of Mars in the past was not only thicker than the thin layer of gases that we are seeing now, but it was also more humid," said Ashwin. Vasadava, a scientist from NASA's Curiosity rover project.
The image shows the current location of the Curiosity rover
Scientific group Curiosity on Monday announced that it had a crater 96 miles wide, on which the rover landed in August 2012, when it was a lake.
"The landscape of Mount Sharpe shows that rivers, lakes and groundwater existed on Mars for millions of years," added Vasadava.
Currently, water on Mars is present only in frozen form at the poles of the planet. Even if the atmosphere were thicker (thereby creating a pressure that would allow water to exist in liquid form, rather than in the form of ice or gas), water would still be predominantly collected in the polar regions, leaving the atmosphere dry. Lake Gail would quickly evaporate. "In order for the lake in the Gale crater to exist for a long period of time, the presence of a large amount of water in the climate system is necessary," said Vasadava.
To create a humid atmosphere on Mars, it was necessary to have a vigorous hydrological cycle, created either by melting with ice closer to the equator, or by the presence of the ocean.
“A humid atmosphere would not allow Gale Lake to evaporate, and would also replenish water reserves with atmospheric precipitation,” Vasadava continued.
Since the 1970s, scientists have been searching for remnants of the Martian ocean. So far they have found only hints, such as networks of valleys and canals, carved in the highlands. However, concrete evidence, such as coastlines, was not found, although it may have been destroyed by erosion.
Even taking into account greenhouse gases, at present computer models are not capable of explaining how, Mars remained warm enough to maintain Lake Gail for millions of years.
"Building a model of the ancient climate of Mars, which would remain warm and humid enough wet for millions of years, turned out to be quite a challenge," said Vasadava.
One option is that Mars periodically heated by the action of volcanoes or changes in the orbit, as a result of a collision with large asteroids.