AIM Satellite Sets Its Sights High

Posted: April 18, 2007 at 1:00 am, Last Updated: November 30, -0001 at 12:00 am

By Catherine Probst

After more than five years of planning, the Aeronomy of Ice in the Mesophere (AIM) Climate satellite is set to launch on April 25 from Vandenberg Air Force Base in California.

Though Michael Summers, professor of planetary science and astronomy at Mason, won’t be there in person, he will be there in spirit as one of the co-investigators of the mission.

The two-year AIM experiment is a NASA space mission designed to study the highest clouds in Earth’s atmosphere — clouds at the edge of space, called Polar Mesospheric Clouds (PMCs).

These clouds are visible from the ground and form in the spring and summer. Made of frozen water, or ice crystals, they form 50 miles high in a layer of the atmosphere called the mesosphere, unlike the more common clouds, which form up to five miles above the surface of Earth.

“The clouds we are studying may be the most sensitive indicator of global warming,” says Summers, an expert in planetary atmospheres. “This mission won’t prove it, but it will help us understand if the two are connected.”

When observed from the ground near twilight when the sun is just below the horizon, these clouds are called Noctilucent Clouds (NLCs), which means “night-shining.” When viewed from space they are called PMCs because they usually form only at high latitudes near the north and south poles.

Since first observed by scientists in 1885, people have reported seeing NLCs at lower latitudes in states such as Utah and Colorado. In addition, NLCs seem to be getting brighter and more frequent. Scientists do not understand why this is happening and are using AIM to try to explain why PMCs form in the first place and if these changes are caused by natural variations in Earth’s atmosphere, or if they are influenced by human activities.

According to Summers, his main purpose in the mission is to understand the participation of water in forming these clouds.

The AIM satellite is 55 inches tall and 43 inches wide and weighs 430 pounds. It will orbit 373 miles above Earth and have three instruments to help observe the chemicals and small dust particles created by the PMCs for at least two years. One instrument is designed to take pictures of the clouds to determine when and where they form and what they look like.

Another instrument called SOFIE will measure the temperature of the mesosphere and how much water vapor is present to determine what combination of these is necessary to freeze the water into ice crystals that form PMCs. In addition, SOFIE will measure the amounts of other gases to tell scientists more about the chemistry and movement of air in the mesosphere that might lead to cloud formation or evaporation.

The third instrument will measure how much dust from meteors enters Earth’s atmosphere. Using this information, scientists want to find out if a tiny speck of dust is necessary to provide a surface on which water vapor condenses and freezes. It is possible that without dust, PMCs are much less likely to form.

For more information about the AIM Climate satellite, visit the web site.

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