Researchers adjusted the chamber's temperature and relative humidity to match conditions on Mars. 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 could help improve conventional models of the Martian atmosphere, many of which assume that Martian clouds require humidity levels similar to those found on Earth, researchers said.
    
"A lot of atmospheric models for Mars are very simple," said Dan Cziczo, Professor of Atmospheric Chemistry at Massachusetts Institute of Technology (MIT).
    
"They have to make gross assumptions about how clouds form: As soon as it hits 100 per cent humidity, boom, you get a cloud to form. But we found you need more to kick-start the process," said Cziczo.
    
Cziczo said 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.
    
The team conducted most of the experiments in 2012 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 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 vapour can adhere to form cloud particles.
    
After "seeding" the chamber, the researchers adjusted the temperature, first setting it to the coldest temperatures at which clouds form on Earth.
    
Throughout the experiment, they cranked the temperature progressively lower, eventually stopping at the chamber's lowest setting, around minus 49 degrees Celsius — "a warm summer's day on Mars," Cziczo said.
    
By adjusting the chamber's relative humidity under each temperature condition, the researchers were able to create clouds under warmer, Earth-like temperatures, at expected relative humidities.
    
Over a week, the group created 10 clouds, with each cloud taking about 15 minutes to form. The chamber is completed insulated, so the researchers used a system of lasers, which beam across the chamber, to detect cloud formation.
    
The study was published in the Journal of Geophysical Research: Planets.

(Agencies)

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