Researchers from the University of California, Berkeley UC link existence of oceans early in Mars history to the rise of the solar system’s largest volcanic system, Tharsis and highlight the key role played by global warming in allowing liquid water to exist on Mars.
In a new study, the team suggests that the oceans formed several hundred million years earlier and were not as deep as once thought.
“Volcanoes may be important in creating the conditions for Mars to be wet,” said Michael Manga, a UC Berkeley professor of earth and planetary science and senior author of a paper.
The new model proposes that the oceans formed before or at the same time as Mars’ largest volcanic feature, Tharsis, instead of after Tharsis formed 3.7 billion years ago. The absence of crustal deformation from Tharsis means the seas would have been shallower, holding about half the water of earlier estimates.
“The assumption was that Tharsis formed quickly and early, rather than gradually, and that the oceans came later,” Michael Manga, professor of earth and planetary science at Berkeley said. “We’re saying that the oceans predate and accompany the lava outpourings that made Tharsis.”
The model also counters another argument against oceans: that the proposed shorelines are very irregular, varying in height by as much as a kilometer, when they should be level, like shorelines on Earth.
This irregularity could be explained if the first ocean, called Arabia, started forming about 4 billion years ago and existed, if intermittently, during as much as the first 20 percent of Tharsis’s growth. The growing volcano would have depressed the land and deformed the shoreline over time, which could explain the irregular heights of the Arabia shoreline.
Similarly, the irregular shoreline of a subsequent ocean, called Deuteronilus, could be explained if it formed during the last 17 percent of Tharsis’s growth, about 3.6 billion years ago.
“These shorelines could have been emplaced by a large body of liquid water that existed before and during the emplacement of Tharsis, instead of afterwards,” said first author Robert Citron, a UC Berkeley graduate student. Citron will present a paper about the new analysis on March 20 at the annual Lunar and Planetary Science conference in Texas.
Tharsis, now a 5,000-kilometer-wide eruptive complex, contains some of the biggest volcanoes in the solar system and dominates the topography of Mars. Earth, twice the diameter and 10 times more massive than Mars, has no equivalent dominating feature. Tharsis’s bulk creates a bulge on the opposite side of the planet and a depression halfway between. This explains why estimates of the volume of water the northern plains could hold based on today’s topography are twice what the new study estimates based on the topography 4 billion years ago.
“This is a hypothesis,” Manga emphasized. “But scientists can do more precise dating of Tharsis and the shorelines to see if it holds up.”