Mars once had an atmosphere that was thicker than Earth's today

image via New Scientist

September 15, 2025, 6:00 PM

• •Mars's early atmosphere could have been far denser than today's.
• •A thick, hydrogen-rich atmosphere may have shielded Mars from asteroid impacts.
• •Scientists estimate the primordial atmosphere had a pressure almost three times Earth's.
• •This atmosphere dissipated within a million years, predating liquid water.

Mars, now with a thin atmosphere, may have had one hundreds of times thicker, potentially shielding it from early asteroid impacts. Scientists suggest a primordial atmosphere, rich in hydrogen, persisted longer than previously thought. This thick atmosphere, equivalent to 2.9 bar pressure, might have diluted cometary material, allowing the planet to avoid some bombardment. The atmosphere was lost relatively quickly, vanishing before the formation of liquid water on Mars.

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