Mars has spectacular, glowing clouds at sunset

Mars, often seen as a dry and dusty world, holds surprising beauty in its skies. While Earth’s clouds are made of water vapor, Martian clouds contain something quite different – frozen carbon dioxide, also known as dry ice.

These clouds appear in stunning shades of red and green, creating an otherworldly spectacle that continues to intrigue scientists.

Recently, NASA’s Curiosity rover captured breathtaking images of these drifting clouds. Taken over 16 minutes on 17 January 2025, these images reveal a fascinating atmospheric phenomenon.

Known as noctilucent, or “night shining” clouds, these spectacular structures glow in the fading light of the setting sun. For this reason, they are also referred to as twilight clouds.

Sometimes, they even display a rainbow-like effect known as iridescence. The more scientists observe these clouds, the more they learn about Mars’s atmosphere and its ever-changing weather patterns.

Formation of clouds on Mars

Martian clouds form under extreme conditions. They exist as either water ice clouds or carbon dioxide ice clouds.

Water-ice clouds tend to form at lower altitudes, while frozen carbon dioxide clouds appear much higher up, where temperatures are even colder.

These dry ice clouds are the only ones on Mars known to create iridescence, when sunlight scatters through the tiny particles and creates a shimmering display of colors.

Curiosity’s latest images show these twilight clouds of dry ice floating at altitudes between 37 and 50 miles (60 to 80 kilometers) above the Martian surface.

As they drift, some plumes fall as low as 31 miles (50 kilometers) before evaporating due to rising temperatures.

This movement offers valuable clues about the Martian atmosphere and how it behaves at different temperatures.

In contrast, water-ice clouds travel in the opposite direction. these clouds hover around 31 miles (50 kilometers) above the rover, forming and dissipating as the atmosphere shifts.

The existence of two types of clouds moving in different directions adds another layer of complexity to the Martian climate.

Discovering Mars’s twilight clouds

Twilight clouds on Mars are not a new discovery. NASA’s Pathfinder mission first spotted them in 1997. However, Curiosity did not observe them until 2019.

When it finally captured its first images of iridescence, scientists realized they had stumbled upon something remarkable.

This marks the fourth Martian year in which Curiosity has recorded twilight clouds. The phenomenon occurs at the start of fall in the planet’s southern hemisphere.

These high-altitude clouds of frozen carbon dioxide glow as the sun dips below the horizon, creating a breathtaking visual effect.

Mark Lemmon, an atmospheric scientist with the Space Science Institute, has studied these clouds extensively.

“I’ll always remember the first time I saw those iridescent clouds and was sure at first it was some color artifact,” he said. “Now it’s become so predictable that we can plan our shots in advance; the clouds show up at exactly the same time of year.”

Scientists use these observations to understand how Martian clouds form. Studying the size and growth rate of cloud particles helps researchers gain deeper insight into the planet’s atmospheric behavior. Each image captured by Curiosity adds to our appreciation of this phenomenon.

Mystery of carbon dioxide clouds

Despite years of observations, one question remains unanswered – why do carbon dioxide twilight clouds appear only in certain regions of the Martian atmosphere?

Curiosity, which explores Gale Crater near the Martian equator, has frequently captured them. Pathfinder, which landed in Ares Vallis, also detected them.

However, NASA’s Perseverance rover, located in Jezero Crater, has yet to record any since its landing in 2021.

Scientists believe that some areas of Mars may be more suitable than others for the formation of these clouds. One possible explanation involves gravity waves, which can cool the atmosphere enough for carbon dioxide to freeze into ice.

However, this process is not fully understood.

“Carbon dioxide was not expected to be condensing into ice here, so something is cooling it to the point that it could happen. But Martian gravity waves are not fully understood and we’re not entirely sure what is causing twilight clouds to form in one place but not another,” Lemmon shared.

This atmospheric mystery continues to challenge scientists. By studying how these clouds appear and change over time, researchers hope to unlock new insights into Martian weather and climate.

Unique perspective from Curiosity’s Mastcam

The latest images of twilight clouds were taken using one of Curiosity’s Mastcam cameras.

However, these images have a distinct appearance. Instead of a full-frame view, the clouds appear within a partially open circle. This is because the filter wheel on the left 34 mm Mastcam has become stuck; this limits its field of view.

Despite this issue, the camera remains functional. The rover’s right 100 mm Mastcam provides higher-resolution, color images that capture a more detailed picture of the Martian skies. These observations continue to help scientists track changes in the atmosphere.

Curiosity recently completed an exploration of the Gediz Vallis channel, an area shaped by ancient water activity. Now, the rover is moving to a new region that is filled with fascinating geological features.

Among them is boxwork, a structure formed by groundwater. These formations look like giant spiderwebs from space.

Investigating Mars’s ancient past

Curiosity’s journey is not just about studying clouds – it also seeks clues about Mars’s past. Recently, the rover visited an impact crater called “Rustic Canyon.”

This small crater, measuring 67 feet (20 meters) in diameter, has lost much of its rim due to erosion. Its shallow depth suggests that it formed millions of years ago.

Scientists study impact craters because they can reveal hidden materials from beneath the surface. When a meteor strikes Mars, it can expose rock layers that have been buried for eons.

These ancient materials may contain preserved organic molecules that offer insights into the planet’s history.

Since Mars’s surface is constantly exposed to radiation, organic molecules tend to degrade over time. However, deeply buried materials have a better chance of remaining intact.

By analyzing samples from craters, researchers hope to understand whether Mars once had conditions suitable for microbial life.

What the future holds

Curiosity’s observations of Martian clouds provide a deeper understanding of the planet’s climate and atmosphere.

Each new image offers valuable information about cloud formation, atmospheric cooling, and seasonal weather changes.

The ongoing mystery of carbon dioxide twilight clouds remains unsolved, but with continued research, scientists may one day uncover the factors that cause them to form in some areas but not others.

As Curiosity moves forward in its mission, it will continue exploring new terrains and capturing more stunning views of the Martian sky.

Each discovery brings humanity one step closer to understanding the Red Planet and its potential for hosting past or present life.

The full study can be read in the Geophysical Research Letters.

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