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Clouds come in countless shapes, from fluffy cotton candy to wispy lines that streak across the sky, but they are all formed from one simple ingredient—water vapor. In an experiment conducted September 19, scientists created the first artificial, high-atmosphere noctilucent cloud. But rather than water, the cloud formed from dust particles spewed out of a rocket.
The project, led by the U.S. Naval Research Laboratory (NRL) in Washington, D.C., focused on fabricating a noctilucent cloud, or one that floats at an altitude of 80 to 100 kilometers in the mesosphere (a layer of the atmosphere starting at about 50 kilometers above the surface). Because these clouds block sunlight, they play a part in, and may one day offer a solution to, global warming. Scientists have been able to use radar to track the behavior of natural noctilucent clouds, gleaning their speeds and densities. But studying artificial clouds offers "more of a controlled situation," says Paul Bernhardt, a senior research associate in the NRL's Plasma Physics Division and leader of the project.* "People [who] study the natural clouds, they have to sit there and wait" to come across one in Earth's upper atmosphere.
Scientists at the NRL and the U.S. Department of Defense Space Test Program set out to form and follow noctilucent clouds, as part of the Charged Aerosol Release Experiment (CARE). They built their rocket using 80s-era solid motors handed down from NASA. Then, when conditions were right, as they were on Saturday evening—meaning there were few natural clouds to obscure the view—the team launched their dust delivery system from NASA Goddard Space Flight Center's Wallops Flight Facility in Virginia.
Although most rocket engines leave a trail of debris close to where they are ignited, Bernhardt explains that the group timed the rocket's fourth stage motor to dump 100 kilograms of aluminum oxide dust after it had reached its peak altitude of around 280 kilometers. By knowing the rocket's exact point of release, researchers at stations ranging from Virginia to New Jersey as well as in Bermuda could point their lasers and wide-angle lens cameras at the cloud's birthplace, off the east coast, to study its behavior.
The CARE scientists managed to pursue the dust cloud for 20 minutes Saturday before losing its trail. In this time, they collected terabytes of data in the form of images and radio signals bounced off the cloud. Although Bernhardt says it could be months before all the data is processed, his assessment of the first run is that "we met every success criterion we had."
Bernhardt is already thinking of how the group will design future cloud-making launches. For one, because noctilucent clouds are usually found at higher latitudes, he thinks that sending a rocket into the atmosphere above Alaska or Norway would give a better idea of these clouds' natural behavior, and perhaps allow researchers to follow one for a longer period. If so, residents in northern latitudes could be treated to quite a show during the next experiment. When light from the setting sun bounced off the CARE dust particles on Saturday evening, some residents in regions ranging from New Jersey to Massachusetts bore witness to "a series of spooky lights."
*Note (9/23/09): This sentence was edited after publication to correct Paul Bernhardt's title.
