Mars Once boasted a Thicker Atmosphere Than Earth’s Today

Mars’ atmosphere may have once been far thicker, providing a protective layer against the frequent asteroid impacts that destroyed other celestial bodies.

Our solar system began forming around 4 billion years ago, and by that time, Mars was nearly fully developed. The planet existed within a vast reservoir of hot gas and dust swirling around a youthful sun, known as the solar nebula, which some planets absorbed into their atmosphere. However, it was believed that as the solar nebula dissipated, Mars would lose this gas, resulting in a thinner atmosphere.

Recently, Sarah Jollett from Paris’ Collège de France and her team propose that Mars retained this gas for a longer period, forming a primordial atmosphere akin to a sustained soup.

Shortly after the nebula receded, it was believed that the orbits of significant planets like Jupiter and Saturn influenced each other, subsequently disturbing the paths of comets and asteroids that headed towards the inner solar system, impacting rocky planets. While chemical signatures of these impacts can be found on Earth, evidence on Mars remains limited.

“All terrestrial planets faced bombardments from comets during this time, and Mars was no exception, so we should observe remnants of this cometary assault on Mars,” Jollett stated at the Europlanet Science Congress held on September 11th in Helsinki, Finland.

Jollett and her colleagues suggest that the dense, hydrogen-rich atmosphere during this era may have diluted comet material that was available for absorption by Mars. By running simulations of the early solar system, they estimated the potential amount of material impacting Mars and compared it to the detectable quantity. They deduced that the original Martian atmosphere had a mass equivalent to 2.9 bars, around three times the atmospheric pressure we experience on the surface today.

However, this atmosphere dissipated relatively swiftly over about a million years, according to Raymond Pierre Hambart from Oxford University, who was not involved in the study. This loss primarily occurred before liquid water could come to the surface of Mars. The necessary clear atmospheric conditions, rich in carbon dioxide, were likely not present in that thick primordial atmosphere.

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