While Mars is widely regarded as a stark and arid planet, its atmosphere reveals breathtaking beauty that captivates scientists. Unlike Earth’s clouds, which predominantly consist of water vapor, the clouds on the Red Planet are formed from frozen carbon dioxide, commonly referred to as dry ice.

These unique clouds exhibit vibrant hues of red and green, offering a mesmerizing view that sparks curiosity among researchers.

Recently, NASA’s Curiosity rover captured stunning photographs of these ethereal clouds. Taken over a span of 16 minutes on January 17, 2025, these images showcase a captivating atmospheric phenomenon.

Known as noctilucent or “night-shining” clouds, these phenomenal structures illuminate in the twilight as the sun sets, leading to their nickname as twilight clouds.

In some instances, they exhibit a rainbow-like effect known as iridescence. As researchers continue to study these clouds, they gain valuable insights into the nuances of Mars’s atmosphere and dynamic weather patterns.

How Mars’s Clouds Form

Clouds on Mars develop under extreme conditions, manifesting either as water ice clouds or carbon dioxide ice clouds.

Water-ice clouds typically form at lower altitudes, while frozen carbon dioxide clouds reside much higher, where temperatures plummet further.

Only carbon dioxide clouds on Mars have the potential to exhibit iridescence, as sunlight scatters through tiny particles in a dazzling show of colors.

Curiosity’s latest images depict these twilight clouds hovering between 37 and 50 miles (60 to 80 kilometers) above the Martian surface. As they drift, some reach altitudes as low as 31 miles (50 kilometers) before evaporating due to rising temperatures.

This movement provides crucial clues about Martian atmospheric conditions and how they fluctuate with varying temperatures.

Conversely, water-ice clouds tend to ascend, lingering around 31 miles (50 kilometers) above the rover, with their formation and dissipation intricately linked to atmospheric changes.

The interplay between these two distinct types of clouds, moving in different directions, adds complexity to Martian climate dynamics.

Unraveling Mars’s Twilight Clouds

The discovery of twilight clouds on Mars is not new. They were first observed by NASA’s Pathfinder mission in 1997, yet Curiosity did not capture evidence until 2019.

Upon photographing iridescent clouds, scientists realized they had uncovered a significant phenomenon.

This marks Curiosity’s fourth Martian year recording twilight clouds, which typically appear at the onset of autumn in the southern hemisphere.

These high-altitude clouds of frozen carbon dioxide create striking visuals as the sun dips below the horizon.

Mark Lemmon, an atmospheric scientist at the Space Science Institute, has extensively researched these clouds.

He remarked, “The first time I witnessed those iridescent clouds, I initially thought it was a color artifact. Now, we’ve learned to predict their appearance, planning our observations around this yearly cycle.”

These insights are crucial for understanding the formation of Martian clouds. Analyzing cloud particle sizes and growth rates enhances researchers’ understanding of atmospheric behavior on the planet. Each image contributes to the growing body of knowledge surrounding this phenomenon.

The Enigma of Carbon Dioxide Clouds

Despite extensive research efforts, one mystery endures: why do carbon dioxide twilight clouds manifest only in specific regions of the Martian atmosphere?

Curiosity, operating in Gale Crater near the equator, frequently captures images of these clouds, as did Pathfinder in Ares Vallis. However, NASA’s Perseverance rover, located in Jezero Crater, has yet to detect any since its arrival in 2021.

This suggests that certain Martian regions may be more conducive to cloud formation than others. One theory posits that gravity waves could cool the atmosphere sufficiently for carbon dioxide to transition into ice.

Yet, this process remains poorly understood.

“We didn’t expect carbon dioxide condensation in this area, indicating something is cooling the atmosphere enough for it to occur. However, Martian gravity waves are not fully understood, which limits our understanding of why twilight clouds form in some locations but not in others,” Lemmon stated.

This ongoing atmospheric riddle poses significant challenges for scientists. By examining the dynamics of cloud formation and their variations over time, researchers aim to gain deeper insights into Martian weather and climate.

Curiosity’s Unique Observations

The latest twilight cloud images were captured using Curiosity’s Mastcam.

These images possess a distinctive quality; the clouds appear in a partially open circle due to a jammed filter wheel on the left 34 mm Mastcam, limiting its field of view.

Nonetheless, the camera continues to operate effectively. The rover’s right 100 mm Mastcam offers higher resolution, color images that deliver more detailed views of the Martian atmosphere. These observations aid scientists in monitoring atmospheric changes.

Curiosity has recently completed its exploration of the Gediz Vallis channel, an area shaped by ancient water flow, and is now heading to a new region filled with intriguing geological structures.

Among these formations is boxwork, characterized by groundwater and appearing as colossal spiderwebs from an aerial perspective.

Exploring Mars’s Ancient History

Curiosity’s mission extends beyond studying clouds; it also investigates the planet’s history. The rover recently visited an impact crater known as “Rustic Canyon.”

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

Scientists examine impact craters as they can unveil hidden materials from beneath the Martian surface. A meteor strike can expose ancient rock layers that have remained buried for extended periods.

These ancient rocks may host preserved organic molecules that could provide critical insights into the planet’s past.

Given Mars’s surface exposure to radiation, organic molecules tend to degrade over time, yet deeply embedded materials have a better chance of remaining intact.

By analyzing samples from craters, scientists aim to determine if Mars ever possessed conditions suitable for microbial life.

Looking Ahead

Curiosity’s observations of Martian clouds deepen our understanding of the planet’s climate and atmosphere.

Every new image yields valuable data on cloud formation, atmospheric cooling, and seasonal weather variations.

While the mystery of carbon dioxide twilight clouds remains unresolved, ongoing research may eventually reveal the factors influencing their formation in specific regions.

As Curiosity continues its mission, it will explore new landscapes and document more breathtaking snapshots of Martian skies.

Each discovery advances humanity’s knowledge of the Red Planet and its potential for harboring life, whether in the past or present.

This comprehensive study can be accessed in the Geophysical Research Letters.

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