The delicate clouds that appear on Mars annually have intrigued astronomers since their initial discovery, likely stemming from a water-rich atmosphere that seems implausible.

Each winter, clouds spanning 1,800 kilometers form near the Arsia Mons, located in the southern hemisphere of Mars, emerging and dissipating daily for nearly three months. The atmospheric conditions on Mars vastly differ from Earth’s, notably with an abundance of fine dust particles that can cause water vapor in the atmosphere to condense into cloud particles. This results in cloud patterns unique to Mars, yet simulations accounting for these high dust levels do not replicate the distinct features of the Arsia Mons Cloud.

Now, Jorge Hernandez Bernal from the University of Sorbonne in France and his team propose that an exceptionally high amount of water vapor in the atmosphere could recreate these cloud characteristics. Elevated levels of water vapor aid in cloud particle formation through alternative dust-free processes known as homogeneous nucleation.

When researchers conducted atmospheric simulations around Arsia Mons that featured increased water content, the resulting cloud formations bore a striking resemblance to the actual clouds.

“Uniform nucleation necessitates much greater water levels on Mars. [Water] saturation is required. Initially, I believed this to be improbable or extremely unlikely on Mars,” said Hernandez Bernal at the Europlanet Science Congress (EPSC) on September 10th, held in Helsinki, Finland. “However, over the last decade, we’ve discovered that Mars can indeed exhibit supersaturation.”