https://phys.org/news/2022-09-clues-ear ... lanet.html
by SETI Institute
New research published in Earth and Planetary Science Letters suggests that Mars was born wet, with a dense atmosphere allowing warm-to-hot oceans for millions of years. To reach this conclusion, researchers developed the first model of the evolution of the Martian atmosphere that links the high temperatures associated with Mars's formation in a molten state through to the formation of the first oceans and atmosphere.
This model shows that—as on the modern Earth—water vapor in the Martian atmosphere was concentrated in the lower atmosphere and that the upper atmosphere of Mars was "dry" because the water vapor would condense out as clouds at lower levels in the atmosphere. Molecular hydrogen (H2), by contrast, did not condense and was transported to the upper atmosphere of Mars, where it was lost to space. This conclusion—that water vapor condensed and was retained on early Mars whereas molecular hydrogen did not condense and escaped—allows the model to be linked directly to measurements made by spacecraft, specifically, the Mars Science Laboratory rover Curiosity.
"We believe we have modeled an overlooked chapter in Mars's earliest history in the time immediately after the planet formed. To explain the data, the primordial Martian atmosphere must have been very dense (more than ~1000x as dense as the modern atmosphere) and composed primarily of molecular hydrogen (H2)," said Kaveh Pahlevan, SETI Institute research scientist.