Curiosity captures images of Martian clouds

Clouds that are probably composed of ice crystals and possibly supercooled water droplets were caught in images by NASA’s Opportunity rover. 

Credit: NASA/JPL/Texas A&M/Cornell

Curiosity celebrated two years on Mars on August 5, 2014, and is continuing its progress across the surface of the planet.

The rover has already fulfilled one of its primary mission goals by confirming that environments theoretically capable of supporting microbial life were once present on ancient Mars.

Now Curiosity is continuing its journey toward the slopes of Mount Sharp and is currently headed for an outcrop dubbed 'Pahrump Hills.

In a tweet on September 2, 2014, Curiosity shared its view of the path ahead and proclaimed:

"Head for the hills! I'm driving towards these hills on Mars to do geology work & also search for clouds."

Curiosity is described as the first roving analytical laboratory on Mars, and has been cruising around the planet these past two years drilling rocks, zapping soil, and photographing layered outcrops.

The geological data that the mission has returned has been invaluable for astrobiologists trying to interpret Mars' past climate conditions but why is Curiosity also taking time to turn its instruments skyward?

Astrobiology Magazine spoke with Dr. Robert M. Haberle, Planetary Scientist at NASA Ames and a team member for the Rover Environmental Monitoring Station (REMS), and asked him why astrobiologists are curious about martian clouds.

"Clouds are part of the planet's climate system," explained Haberle. "Their behaviour tells us about winds and temperatures."

Studying weather and clouds on Mars today can shed light on processes that have shaped the planet's climate through time.

Bob M. Haberle

"Some studies suggest that clouds in the past may have significantly warmed the planet through a greenhouse effect. A warmer environment is more conducive to life," said Haberle.

Clouds are also connected to wind and weather patterns, and studying weather is important for interpreting how natural processes have shaped the rocks, dunes and outcrops that Curiosity has been photographing.

Haberle points out that, "winds are the primary mechanism for shaping the planet's surface for the past 3-4 billion years.

Studying martian weather can not only help us understand Mars' current climate, but also provides clues about its past environment and the physical processes that operate on the planet.

This information can in turn help astrobiologists interpret the planet's geological record.

REMS is an environmental monitoring station composed of six different sensors.

The instrument collects daily and seasonal data on wind, pressure, relative humidity, temperature and ultraviolet radiation at the martian surface.

REMS was contributed to the Mars Science Laboratory (MSL) mission by the the Centro de Astrobiologia (CAB) in Spain.

Martian clouds form in much more humid conditions

Clouds captured above a vast plain of sand by the Opportunity rover near Victoria Crater on Mars on October 2006. Credit: NASA

At first glance, Mars' clouds might easily be mistaken for those on Earth: Images of the Martian sky, taken by NASA's Opportunity rover, depict gauzy, high-altitude wisps, similar to our cirrus clouds.

Given what scientists know about the Red Planet's atmosphere, these clouds likely consist of either carbon dioxide or water-based ice crystals.

But it's difficult to know the precise conditions that give rise to such clouds without sampling directly from a Martian cloud.

Researchers at MIT have now done the next-best thing: They've recreated Mars-like conditions within a three-story-tall cloud chamber in Germany, adjusting the chamber's temperature and relative humidity to match conditions on Mars—essentially forming Martian clouds on Earth.

While the researchers were able to create clouds at the frigid temperatures typically found on Mars, they discovered that cloud formation in such conditions required adjusting the chamber's relative humidity to 190 percent—far greater than cloud formation requires on Earth.

The finding should help improve conventional models of the Martian atmosphere, many of which assume that Martian clouds require humidity levels similar to those found on Earth.

Dan Cziczo

"A lot of atmospheric models for Mars are very simple," says Dan Cziczo, the Victor P. Starr Associate Professor of Atmospheric Chemistry at MIT.

"They have to make gross assumptions about how clouds form: As soon as it hits 100 percent humidity, boom, you get a cloud to form. But we found you need more to kick-start the process."

Cziczo says the group's experimental results will help to improve Martian climate models, as well as scientists' understanding of how the planet transports water through the atmosphere.

He and his colleagues have reported their findings in Journal of Geophysical Research: Planets.

Seeding Martian clouds
The team conducted most of the study's experiments during the summer of 2012 in Karlsruhe, Germany, at the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) facility—a former nuclear reactor that has since been converted into the world's largest cloud chamber.

The facility was originally designed to study atmospheric conditions on Earth. But Cziczo realized that with a little fine-tuning, the chamber could be adapted to simulate conditions on Mars.

To do this, the team first pumped all the oxygen out of the chamber, and instead filled it with inert nitrogen or carbon dioxide—the most common components of the Martian atmosphere.

They then created a dust storm, pumping in fine particles similar in size and composition to the mineral dust found on Mars.

Much like on Earth, these particles act as cloud seeds around which water vapor can adhere to form cloud particles.