Ancient crater lakes on Mars could have hosted life

What were the lakes of Mars like?

The only liquid water on Mars today is thought to exist deep underground, although water ice exists in polar ice caps and as permafrost. Over 4.1 billion years ago, however, there was much more water.

At this time, Earth’s close neighbor is thought to have had a magnetic field that deflected the solar wind away from the planet, allowing greenhouse gases to remain in the atmosphere and water to exist on the surface in liquid form.

The planet’s core was subsequently demagnetized for reasons that are still debated, with some suggesting that meteorite impacts may have been responsible.

The superfast subatomic particles contained in the solar wind then entered Mars’ atmosphere and began to strip the planet of its greenhouse gases, including water vapor. This caused the planet to cool and dry significantly, with any remaining liquid water frozen into ice.

But after this, periods of volcanic activity released more greenhouse gases into the atmosphere, raising the planet’s temperature for a time and allowing liquid water to form lakes again.

“On Earth, there are different ways in which a lake basin can form, but the lakes on Mars are generally formed in the same way,” says Javier. ‘The only way new basins can be generated is by impact craters left by large meteorites.’

“These craters were then fed by inlets or groundwater that filled them up over time, with some forming part of larger channel systems that can still be seen today.”

However, these lakes would have been short-lived, at least compared to those on Earth. They are estimated to have existed for anywhere from a million to as little as 100 years, partly as a result of Mars’ weak gravity.

“Mars has lower gravity than Earth, which means there is less compaction of sediments under lakes across the planet,” says Javier. “This makes the soil more porous, which makes it easier for water to drain into the ground and causes the lake to dry out quickly if the water supply slows down.”

Lower gravity would also cause sediment to have been suspended in the water for longer, meaning Martian lakes were likely murky. This could have had consequences for all previous inhabitants of the planet.

“Sediments in the water would limit the depth light could penetrate into these lakes,” says Javier. ‘The photic zone on early Mars would have been about 10 times shallower than it is on modern Earth as a result of this, as well as the Sun being fainter at the time.’

“This would have had implications for photosynthetic life if it ever developed on Mars. On the other hand, suspended sediment would have been a major advantage for other types of microorganisms.’