Thursday, June 3, 2021

Ancient Mars' Rivers and Lakes

 From Space:

Cloudy skies may have allowed water to flow on Mars long ago. Though the Red Planet is a frigid desert today, around four billion years ago it hosted relatively long-lived lakes and river systems, as observations by NASA's Curiosity rover and other Mars robots have shown.

Mars' atmosphere was much thicker back then, which helped to keep liquid surface water from boiling away. However, it remains unclear how that water could have been liquid in the first place; the sun was about 30% dimmer during that ancient epoch than it is today, so the Martian surface should seemingly have been a permanent winter wonderland. A new study may help to solve this puzzle. A thin layer of icy clouds high in the Martian atmosphere could have provided a greenhouse effect, warming the planet for long stretches, researchers found.

"There's been an embarrassing disconnect between our evidence and our ability to explain it in terms of physics and chemistry," lead author Edwin Kite, a planetary scientist at the University of Chicago, said in a statement. "This hypothesis goes a long way toward closing that gap."

This cloud idea was first proposed nearly a decade ago but fell out of favor because "it was argued that it would only work if the clouds had implausible properties," Kite said. For example, previous modeling work suggested that water would have had to persist for unrealistically long periods in the Martian atmosphere for the clouds to do their warming work. However, the new modeling work by Kite and his colleagues indicates that wispy but warming clouds could indeed have formed high above the planet, trapping enough heat for liquid water to persist on the surface — but only if certain conditions were met.(Read more.)

No comments: