Scientists explain Mars's 1,800-km cloud via homogeneous nucleation

A Nature Geoscience paper led by Jorge Hernández-Bernal of Sorbonne University attributes the Arsia Mons Elongated Cloud to homogeneous nucleation — water vapor freezing without dust seeds. The Mars Planetary Climate Model shows air cooling 30 °C in under 15 minutes to −143 °C at roughly 10 million percent humidity and just 0.1 dust grains per cubic centimeter.

• The 1,800-km Arsia Mons cloud appears every Martian summer
• Air cools 30 °C in under 15 minutes to −143 °C
• Summer dust density is only 0.1 grains per cubic centimeter
• Humidity in the freezing zone reaches about 10 million percent