Source: Journal of Geophysical Research: Planets
Geological evidence on Mars indicates that 3.6 billion years ago, an intense pulse of water carved rivers and lakes across the planet, an abrupt shift from the preceding 500-million-year era of much gentler fluvial activity. Researchers have long puzzled over the cause. A new study by Buhler shows, paradoxically, that the collapse of the Martian atmosphere and entry into a colder climate may have melted the polar ice cap and triggered global-scale flooding.
Mars’s atmosphere is primarily made of carbon dioxide gas. It began thinning billions of years ago until about 3.6 billion years ago, the atmosphere became so thin that it froze, collapsing to the ground in its solid form, dry ice.
At this time, Mars had a huge water ice sheet over its south pole. Buhler modeled the effect of the atmosphere freezing on top of this water ice. In the model, the dry ice layer acted as a thermal blanket, holding in heat produced by the Martian interior and causing some of the underlying water ice to melt. In total, about 4% to 40% of the water ice could have melted, an amount of water equivalent to between 20% and 200% of the water currently found near the surface on Mars.
The model showed the meltwater could feed a system of rivers and fill a huge crater called Argyre Basin past its brim, creating a lake the size of the Mediterranean Sea. The modeled river and lake system would have existed beyond the edge of the south polar ice sheet, where globally cold climate conditions would have caused their surfaces to freeze. Rivers could have carried water almost 10,000 kilometers from the south pole to the northern plains. So far, Buhler wrote, this is the only plausible mechanism yet identified that could produce enough water to fill Argyre Basin past its brim.
Formation of the Argyre paleolake could have sparked a hydrologic cycle that lasted for around 100 million years, until the continuous slow loss of carbon dioxide to space depleted the effectiveness of the dry ice thermal blanket. Water from the lake may have evaporated, recondensed at the poles, and then traveled once again to the lake. (Journal of Geophysical Research: Planets, https://doi.org/10.1029/2024JE008608, 2024)
—Saima May Sidik (@saimamaysidik), Science Writer
