Brief
Study suggests Mars cloud forms without dust particles
Researchers propose that the elongated cloud over Arsia Mons can develop through homogeneous nucleation, bypassing the usual dust‑driven mechanism.
By Felo News Desk · Published
A study combining Mars Express observations with a high‑resolution meteorological model proposes that the elongated cloud forming downwind of Arsia Mons volcano may arise from homogeneous nucleation, a cloud‑formation process that does not require dust particles, according to scitechdaily.com.
What happened
The Arsia Mons Elongated Cloud (AMEC) appears each morning during the Martian spring and summer in the southern hemisphere, stretching up to 1,800 km before dissipating. Researchers used data from the European Space Agency’s Mars Express spacecraft, which first captured the cloud in 2018, to feed an advanced model that simulates atmospheric dynamics over the volcano.
What the reports add
The model shows that the towering 20‑km‑high volcano generates a powerful atmospheric wave that lifts moist air parcels rapidly, cooling them by about 30 °C in ten minutes and driving relative humidity to extreme levels. This rapid cooling creates conditions where water vapor can transition directly into ice crystals without the usual dust‑mediated heterogeneous nucleation. The study notes that such homogeneous nucleation requires relative humidity far exceeding 100,000 times typical Earth values, a regime previously only theorised for the upper atmospheres of Earth and Venus.
What was said
"For the AMEC, it seems that cloud formation takes place without needing any of this ‘stuff’," said Jorge Hernández‑Bernal of LMD/CNRS/Sorbonne Université, lead author of the study. "Water vapor turns directly into icy cloud particles without any middle step. It’s akin to droplets of condensation appearing in the middle of a room, rather than on a window. We call this homogeneous nucleation, and we’ve never seen it before in a planetary atmosphere. It’s wholly unexpected." He added that the findings suggest Mars’ humidity can reach the extreme levels required for this process.
How it came about
The AMEC was first identified by Mars Express in 2018, and subsequent observations over several Martian years have documented its regular appearance. Earlier Felo News coverage highlighted other Mars atmospheric studies, including a 2026 report on the low dust content of the planet’s north polar ice (Mars north polar ice dust study). The new research builds on that work by exploring how localized topography can create micro‑climates capable of unprecedented cloud‑formation mechanisms.
Key facts
- The Arsia Mons Elongated Cloud can stretch up to 1,800 km before evaporating. (scitechdaily.com)
- Modeling suggests the cloud forms via homogeneous nucleation, bypassing dust particles. (scitechdaily.com)
- Homogeneous nucleation requires relative humidity over 100,000 times typical Earth levels. (scitechdaily.com)
- Jorge Hernández‑Bernal is the lead author of the study and is affiliated with LMD/CNRS/Sorbonne Université. (scitechdaily.com)
Sources
- [1] scitechdaily.com — originally reported as “Mars’s Strangest Cloud Just Got Even Stranger”
