Scientists Made Martian Clouds in a Nuclear Reactor

Even with its ice caps and striking resemblance to Arizona, maybe the most Earth-like thing on Mars are its clouds. Look at them wisp by in this GIF taken by Phoenix lander in 2008.

But the Martian atmosphere is so different from Earth’s—it’s much colder and has almost no oxygen and much lower levels of nitrogen—that atmospheric scientists could only guess how the clouds formed on the Red Planet. They couldn’t be sure. So, naturally, MIT researchers went to a decommissioned nuclear reactor in Germany that has been refashioned as a three-story cloud chamber and tried to bring the Martian atmosphere to Earth.

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 Martian atmosphere is 95 percent carbon dioxide. 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 acted like cloud seeds, allowing water vapor to adhere to them to form cloud particles.

Then the scientists cooled the chamber down.

As the chamber cooled and approached ever-more Mars-like conditions, the researchers realized that it took more humidity to get clouds to form. Over a week, the researchers made 10 clouds, and they found that clouds forming in cooler conditions—down to -120 degrees Fahrenheit which is like a warm summer day on Mars—needed extremely high relative humidity in order for water vapor to form an ice crystal around the dust to form clouds.

“A lot of atmospheric models for Mars are very simple,” said Dan Cziczo, an 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.”

Instead, the researchers found that it took 190 percent humidity for clouds to form, which is bound to change some assumptions about the air on Mars, as the results are published in the Journal of Physical Research: Planets.

According to Nilton Renno, a professor of atmospheric, oceanic, and space sciences at the University of Michigan, the research suggests that the polar regions of Mars are much more moist than scientists were expecting.

Personally, knowing that Mars is both freezing and humid—not to mention beset with dust storms—makes me want to visit even less, so I guess I'm glad that if I need to see it, Martian weather is available over in Germany.