For decades, scientists studying Mars have known the planet wears a thin veil of clouds — ghostly wisps of water ice drifting high in its atmosphere. But until now, nearly all of our cloud observations came from a single time of day: the Martian afternoon. Like reading just one chapter of a book, this left an incomplete picture of how these clouds form, evolve, and vanish over a full day.
Now, thanks to the Emirates Mars Mission’s Hope probe, that story is finally filling in. Using its unique vantage point, scientists have captured the first comprehensive view of nighttime clouds on Mars, revealing unexpected patterns that may reshape our understanding of the planet’s climate.
The results, published in the Journal of Geophysical Research: Planets, show that Mars’s nights are far from still — in fact, they may be cloudier than its days.
The Thin Air of a Cold World
Mars’s atmosphere is just one-hundredth as dense as Earth’s and is mostly carbon dioxide. Yet, it can still host clouds made of tiny ice crystals formed from the planet’s scarce water vapor. These clouds subtly affect how heat is trapped or released in the Martian air, playing a role in the planet’s weather and climate cycles.
On Earth, we’ve learned that clouds influence everything from temperature to rainfall. On Mars, they may be even more important, since small shifts in atmospheric circulation can have large effects on surface conditions. Understanding them isn’t just a matter of curiosity — it’s a step toward predicting weather on Mars, an essential skill for future human explorers.
The Advantage of Hope’s Orbit
The Hope spacecraft, launched by the United Arab Emirates in 2020 and orbiting Mars since 2021, is the first mission specifically designed to monitor the Martian atmosphere at all times of day and across most latitudes. Its highly elliptical orbit lets it sweep over the planet in ways that complement other spacecraft, which often circle at fixed times of day.
For this study, lead researcher Samuel Atwood and colleagues used nearly two full Martian years’ worth of observations from Hope’s Emirates Mars Infrared Spectrometer. This instrument detects clouds by measuring how they absorb and scatter infrared light, allowing scientists to estimate their presence and thickness both in sunlight and under the dim glow of Mars’s moons, Phobos and Deimos.
A Cloudier Night Than Expected
The analysis revealed a surprise: for much of the Martian year, nighttime clouds are thicker on average than those seen during the day. Instead of being evenly spread out, their behavior followed a rhythm. Peaks in cloudiness tended to occur in the early morning and in the evening, with a distinct lull around midday.
During Mars’s cold season, the patterns became even more striking. A narrow band of especially thick clouds formed near the equator, reaching their maximum just after sunrise. In the evenings, clouds often appeared over a much broader swath of low-latitude regions, while early-morning clouds clustered over the Tharsis volcanic plateau — a massive geological feature stretching along the equator.
The Tharsis region, home to some of the largest volcanoes in the solar system, appears to influence local weather patterns, possibly by altering airflow and trapping moisture.
Why It Matters
These findings are more than just a meteorological curiosity. Mars’s clouds are both a product and a driver of the planet’s atmospheric circulation. By capturing their full daily cycle for the first time, scientists can now test and refine computer models of Martian weather with greater accuracy.
Better models mean better predictions — not only for future robotic missions that must navigate dust storms and temperature swings but also for eventual human crews who will depend on reliable weather forecasts for safety.
A Broader Vision for Mars Science
The Emirates Mars Mission was always intended to complement the work of NASA, ESA, and other space agencies by filling gaps in our knowledge. By revealing the hidden face of Mars’s clouds, Hope has done exactly that.
“Until now, we were mostly blind to what happens in the Martian sky at night,” Atwood noted in a statement. “Hope’s unique orbit has finally opened that window.”
As scientists continue to analyze Hope’s data, more surprises are likely to emerge — from seasonal weather shifts to long-term climate changes. And while the idea of “nighttime clouds on Mars” might sound poetic, it’s also profoundly practical. For a world where every drop of water and every degree of temperature matters, understanding these clouds could be a key piece of the puzzle in making Mars a home for future explorers.
More information: Samuel A. Atwood et al, The Full Diurnal Cycle of Mars Water‐Ice Cloud Optical Depth in EMIRS Observations, Journal of Geophysical Research: Planets (2025). DOI: 10.1029/2025JE008961
