Mars’s oceans APPEARED EARLY
New theory could explain why Mars’s water has disappeared
Mars’s oceans could have been around several hundred million years earlier than formerly believed. A novel scenario suggests that the oceans formed four billion years ago at the same time as the largest volcanic structure on Mars, Tharsis – the volcanic plateau near the planet’s equator that is home to Olympus Mons.
“The assumption was that Tharsis formed quickly and early, rather than gradually, and that the oceans came later,” says Michael Manga from University of California, Berkeley, who took part in the study. “We’re saying that the oceans predate and accompany the lava outpourings that made Tharsis.”
The mineral composition and topography of Mars suggest that there was once a huge ocean covering its northern hemisphere. However, several key questions that challenge this theory remain, such as what happened to all the water? And why is the supposed shoreline not level?
The first of these issues is caused by current estimates for the oceans’ volume, which are too large. If there had been as much water on Mars as currently predicted, it would not have had time to completely evaporate into space or freeze into permafrost. However, these estimates are based on the current landscape, which is deformed by the Tharsis region. If the oceans had formed before or at the same time as the volcanic structure, they would have been much shallower.
The new simulations could also explain why the geological features thought to be the ancient shoreline are uneven. On Earth, shorelines are all at sea level, but those on Mars vary in elevation. But if the ocean and its coast formed when Tharsis was young, the landscape would have changed as the region grew, deforming the shoreline in the process.
“These shorelines could have been put in place by a large body of liquid water that existed before and during the emplacement of Tharsis, instead of afterwards,” says University of California, Berkeley graduate Robert Citron, who led the study.
The current work is all theoretical, but the InSight lander heading to Mars this month could help test the concept by mapping the Martian interior and examining the planet’s volcanic past.
“This is a hypothesis,” stresses Manga about the study’s findings. “But scientists can do more precise dating of Tharsis and the shorelines to see if it holds up.” https://www.berkeley.edu/