Mars, a planet often depicted as arid and desolate, offers a breathtaking display in its skies. Unlike Earth’s water vapor clouds, Martian clouds consist of frozen carbon dioxide, known as dry ice. These icy formations create a mesmerizing visual spectacle that continues to captivate scientists.

Recently, NASA’s Curiosity rover captured stunning images of these drifting clouds. Taken over 16 minutes on January 17, 2025, these snapshots reveal fascinating aspects of an ongoing atmospheric phenomenon.

Noctilucent Clouds: A Mars Mystery

These clouds are referred to as noctilucent or “night shining” clouds, also known as twilight clouds. They glow in the fading light of the setting sun, creating an ethereal display. Occasionally, they even exhibit a rainbow-like effect known as iridescence.

Observations of these clouds provide valuable insights into Mars’s atmosphere and its dynamic weather patterns. Scientists are using Curiosity’s images to enhance their understanding of the planet’s atmospheric dynamics.

Formation of Clouds on Mars

Martian clouds form under extreme conditions, existing as either water ice clouds or carbon dioxide ice clouds. Water-ice clouds tend to form at lower altitudes, whereas carbon dioxide clouds appear higher, around 37 to 50 miles (60 to 80 kilometers) above the Martian surface.

As these clouds drift, some descend to 31 miles (50 kilometers) before evaporating due to rising temperatures. This vertical movement sheds light on the Martian atmosphere and its behavior at different temperatures.

In contrast, water ice clouds move in the opposite direction and hover around 31 miles (50 kilometers) above the Martian surface, forming and dissipating as the atmosphere changes.

Discovering Mars’s Twilight Clouds

Twilight clouds on Mars were first observed by NASA’s Pathfinder mission in 1997. Curiosity did not capture its first images until 2019, and it is the fourth Martian year in which these formations have been recorded.

These high-altitude clouds of frozen carbon dioxide glow during sunset, creating a visually stunning effect. They primarily occur at the start of fall in the southern hemisphere of Mars.

Mark Lemmon, an atmospheric scientist, has extensively studied these clouds. Initially skeptical about the first sighting, he now predicts their appearances with confidence.

“I’ll always remember the first time I saw those iridescent clouds and was sure at first it was some color artifact. 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.”

The Mystery of Carbon Dioxide Clouds

Despite years of observation, the reason behind the exclusive appearance of carbon dioxide twilight clouds in certain regions of Mars remains unresolved. Curiosity, located near the Martian equator, frequently captures them. Similarly, Pathfinder, in Ares Vallis, detected them. However, Perseverance, in Jezero Crater, has yet to record any.

Scientists hypothesize that gravity waves might be responsible for cooling the atmosphere enough for carbon dioxide to condense into ice. However, the mechanism 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.”

This atmospheric puzzle continues to challenge scientists. Ongoing research aims to unlock new insights into the Martian weather.

Unique Perspective from Curiosity’s Mastcam

The latest images of twilight clouds were captured using Curiosity’s Mastcam cameras. However, one of the Mastcam filters has malfunctioned, limiting the field of view. Despite this, the camera remains operational.

Curiosity recently explored the Gediz Vallis channel, shaped by ancient water activity, and is now moving to a new region filled with fascinating geological features, including boxwork formations that resemble giant spiderwebs.

Investigating Mars’s Ancient Past

Beyond studying clouds, Curiosity seeks clues about Mars’s past. Recently, it visited Rustic Canyon, a 20-meter-diameter impact crater that has lost much of its rim due to erosion.

Impact craters reveal hidden materials from beneath Mars’s surface, offering insights into the planet’s history. Buried organic molecules in these craters could hold clues about past microbial life on Mars.

The Future of Martian Cloud Research

Curiosity’s observations of Martian clouds contribute significantly to our understanding of the planet’s climate and atmosphere. Each image offers valuable information about cloud formation, atmospheric cooling, and seasonal weather changes.

The mystery of twilight clouds remains unsolved, but with continued research, scientists may eventually unravel the factors that cause them to form in specific areas. As Curiosity explores new terrains, it continues to capture breathtaking views of the Martian sky, bringing us closer to understanding this enigmatic Red Planet.

For more detailed information, the study is available in the Geophysical Research Letters.