Rare high-altitude clouds found on Mars

August 28, 2006

Planetary scientists have discovered the highest clouds above any planetary surface. They found them above Mars using the SPICAM instrument on board ESA's Mars Express spacecraft. The results are a new piece in the puzzle of how the Martian atmosphere works.

Until now, scientists had been aware only of the clouds that hug the Martian surface and lower reaches of the atmosphere. Thanks to data from the SPICAM Ultraviolet and Infrared Atmospheric Spectrometer onboard Mars Express, a fleeting layer of clouds have been discovered at an altitude between 80 and 100 kilometres. The clouds are most likely composed of carbon dioxide.

SPICAM made the discovery by observing distant stars just before they disappeared behind Mars. By looking at the effects on the starlight as it travelled through the Martian atmosphere, SPICAM built up a picture of the molecules at different altitudes. Each sweep through the atmosphere is called a profile.

The first hints of the new cloud layer came when certain profiles showed that the star dimmed noticeably when it was behind the 90-100 kilometre high atmospheric layer. Although this happened in only one percent of the profiles, by the time the team had collected 600 profiles, they were confident that the effect was real.

"If you wanted to see these clouds from the surface of Mars, you would probably have to wait until after sunset" says Franck Montmessin, a SPICAM scientist with Service d'Aeronomie du CNRS, Verrières-le-Buisson, France, and lead author of the results. This is because the clouds are very faint and can only be seen reflecting sunlight against the darkness of the night sky. In that respect, they look similar to the mesospheric clouds, also known as noctilucent clouds, on Earth. These occur at 80 kilometres altitude above our planet, where the density of the atmosphere is similar to that of Mars' at 35 kilometres. The newly discovered Martian clouds therefore occur in a much more rarefied atmospheric location.

At 90-100 kilometres above the Martian surface, the temperature is just -193° Celsius. This means that the clouds are unlikely to be made of water. "We observe the clouds in super-cold conditions where the main atmospheric component CO2 (carbon dioxide), cools below its condensation point. From that we infer that they are made of carbon dioxide," says Montmessin.

But how do these clouds form? SPICAM has revealed the answer by finding a previously unknown population of minuscule dust grains above 60 kilometres in the Martian atmosphere. The grains are just one hundred nanometres across (a nanometre is one thousand-millionth of a metre).

They are likely to be the 'nucleation centres' around which crystals of carbon dioxide form to make clouds. They are either microscopic chippings from the rocks on the surface on Mars that have been blown to extreme altitudes by the winds, or they are the debris from meteors that have burnt up in the Martian atmosphere.

The new high-altitude cloud layer has implications for landing on Mars as it suggests the upper layers of Mars' atmosphere can be denser than previously thought. This will be an important piece of information for future missions, when using friction in the outer atmosphere to slow down spacecraft (in a technique called 'aerobraking'), either for landing or going into orbit around the planet.
-end-


European Space Agency

Related Mars Articles from Brightsurf:

Water on ancient Mars
A meteorite that originated on Mars billions of years ago reveals details of ancient impact events on the red planet.

Surprise on Mars
NASA's InSight mission provides data from the surface of Mars.

Going nuclear on the moon and Mars
It might sound like science fiction, but scientists are preparing to build colonies on the moon and, eventually, Mars.

Mars: Where mud flows like lava
An international research team including recreated martian conditions in a low-pressure chamber to observe the flow of mud.

What's Mars made of?
Earth-based experiments on iron-sulfur alloys thought to comprise the core of Mars reveal details about the planet's seismic properties for the first time.

The seismicity of Mars
Fifteen months after the successful landing of the NASA InSight mission on Mars, first scientific analyses of ETH Zurich researchers and their partners reveal that the planet is seismically active.

Journey to the center of Mars
While InSight's seismometer has been patiently waiting for the next big marsquake to illuminate its interior and define its crust-mantle-core structure, two scientists, have built a new compositional model for Mars.

Getting mac and cheese to Mars
Washington State University scientists have developed a way to triple the shelf life of ready-to-eat macaroni and cheese, a development that could have benefits for everything from space travel to military use.

Life on Mars?
Researchers from Hungary have discovered embedded organic material in a Martian meteorite found in the late 1970s.

New evidence of deep groundwater on Mars
Researchers at the USC Arid Climate and Water Research Center (AWARE) have published a study that suggests deep groundwater could still be active on Mars and could originate surface streams in some near-equatorial areas on Mars.

Read More: Mars News and Mars Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.