For years, a strange atmospheric phenomenon on Mars has baffled planetary scientists. Every spring and summer, a thin, wispy cloud emerges near the Arsia Mons volcano, stretching over 1,000 miles before vanishing. First recorded by a probe in 2018, this formation, known as the Arsia Mons Elongated Cloud (AMEC), defied explanation until now.
Researchers have finally modeled the cloud’s formation, attributing it to a physical process never before directly observed in any planetary atmosphere. The findings, published in Nature Geoscience, suggest that the cloud forms through homogeneous nucleation, a process where water vapor turns directly into ice crystals without the aid of dust or other particles.
Exotic Physics on the Red Planet
Jorge Hernández-Bernal, a planetary scientist at Sorbonne Université in Paris and the lead author of the study, described the discovery as a breakthrough in understanding Martian weather. He noted that the simulations required including physics that are typically treated as theoretical.
“We found that we needed to include some exotic physics … physics that, while included in textbooks, is treated as theoretical and usually thought not to happen in nature,” Hernández-Bernal said. “Once we included this physics in our simulations, the AMEC emerged just as we hoped.”
On Earth, clouds form when water vapor condenses around tiny particles like dust or salt. The new model suggests that on Mars, the vapor changes state on its own. Hernández-Bernal compared this to condensation appearing in the middle of a room rather than on a cold window. This process requires extreme conditions, including a sharp temperature drop of 30 degrees Celsius within ten minutes and relative humidity levels more than 100,000 times greater than anything measured on Earth.
The Role of Arsia Mons
The Arsia Mons volcano, which rises 65,000 feet into the Martian sky, plays a critical role in creating these conditions. When wind currents hit the massive peak, they generate powerful waves that launch moist air high into the atmosphere in a matter of minutes. This rapid ascent triggers the homogeneous nucleation, allowing the cloud to elongate across the planet.
Scientists had long assumed similar phenomena could occur in the upper atmospheres of other planets, including Venus and Earth. However, the extreme humidity required for such events had never been observed. The new study confirms that these humidity levels exist on Mars, a fact that was previously unknown due to limited atmospheric data.
“We don’t have nearly as much information about Mars’ atmosphere as we do about Earth’s, so reproducing the AMEC to this degree is a big success,” Hernández-Bernal added. “The result is remarkable.”
This discovery provides a concrete explanation for a recurring Martian weather pattern that has persisted for months. It also opens new avenues for understanding atmospheric dynamics on other worlds where direct observation remains challenging.
Source: Wired
