THERE are faint, mysterious objects orbiting high above the Earth that NASA believes could be gossamer-thin sheets of insulation torn from satellites. Their relatively high speed could make them a danger to working satellites.
Early this year, astronomers from the European Space Agency using a 1-metre telescope in the Canary Islands to scan the skies above the equator reported seeing about 55 faint objects, each about 30 centimetres across. They appeared to be orbiting once a day, tens of thousands of kilometres above the Earth. But unlike geosynchronous satellites, which also take a day to circle the equator, these objects follow highly elongated routes.
These “eccentric” orbits could be explained if the objects were extremely light, weighing about 50 grams per square metre. This would make them highly susceptible to the pressure exerted upon them by photons from the sun, says J-C Liou, an astronomer at Lockheed Martin Space Operations in Houston, Texas, who calculated the orbits of various kinds of debris, along with NASA colleague Jonathan Weaver.
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Pat Seitzer, an astronomer at the University of Michigan in Ann Arbor, who has observed the faint objects with a telescope in Chile, agrees. “You can think of it like throwing up a piece of paper,” he says. “The paper flops back and forth on its way down, but a pen goes straight down.” Just as the paper’s relatively large surface area increases the effect of air resistance, so the space debris is heavily influenced by solar radiation.
But Liou’s calculations suggest that even a piece of paper would be too dense to explain the eccentric orbits. However, the thin layers of satellites’ thermal blankets – made of aluminised Mylar, for example, and used to shield satellites from radiation, cold and impacts from space debris – fit the bill perfectly.
The layers, which are not glued together, have been observed peeling off satellites flying at altitudes below about 2000 kilometres. Now, Liou and colleagues believe high-flying geosynchronous satellites, which orbit at altitudes of about 36,000 kilometres, shed them as well, because of impacts from small meteoroids, or satellite explosions.
It is not yet clear what risk the debris poses to working satellites. The stretched-out orbits of these objects mean that they cross the paths of satellites for only short periods of time. But if they do collide with spacecraft, they could pack a bigger punch than ordinary debris, hitting with speeds of more than 1 kilometre per second.
Both Seitzer and ESA will continue to study them. Liou’s calculations show that if the objects are indeed blankets, their orbits should change throughout the year as the Earth orbits the sun. “If we can identify those as pieces of thermal blankets, the logical way to mitigate it is to talk to the manufacturers of the blankets to come up with a better design,” he says.