Clouds of Mars Created on Earth

Inside a defunct nuclear reactor in Karlsruhe, Germany, a team of researchers spent the last year working on an out-of-this-world project: they sought to recreate the atmosphere on Mars inside the world's largest cloud chamber.

The three-story tall cloud chamber, housed at the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) facility, is typically used for closer-to-Earth experiments, but with a bit of fine tuning, climate researchers were able to generate the temperature and relative humidity necessary for the creation of the wispy, cirrus-like clouds common on Mars, effectively creating Martian clouds here on Earth.

Martian temperatures are much colder than what we feel here on Earth, and the researchers from MIT learned that for clouds to form at such icy temperatures, the relative humidity must be 190 percent -- far greater than what's required for cloud formation on Earth. The find debunks a common assumption that cloud formation on Mars would occur at humidity levels similar to Earth clouds.

"A lot of atmospheric models for Mars are very simple," said Dan Cziczo, a 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."

On Earth, the coldest temperature at which clouds can form is around minus 81 degrees Fahrenheit (-63 C). Throughout their experiment, Cziczo and his colleagues gradually made the cloud chamber colder and colder, eventually maxing out the chamber's cooling units at minus 120 F (-84 C), which on Mars is "a warm summer's day" Cziczo notes.

The researchers created a total of 10 clouds in one week, each one taking about 15 minutes to form. Since the clouds were generated in a sealed chamber, the researchers could make assessments of their creations by measuring the scattering of laser light directed at the clouds.

"If we want to understand where water goes and how it's transported through the atmosphere on Mars, we have to understand cloud formation for that planet," Cziczo said. "Hopefully this will move us toward the right direction."

Future research is planned once upgrades to the cloud chamber are complete, allowing it to generate even colder temperatures that are closer to the icy conditions on Mars.

Cziczo and his team's research is published in the Journal of Geophysical Research: Planets.