Earth’s UV Signature Revealed

On its way to rendezvous with a comet, the spacecraft Rosetta turned an eye toward Earth and recorded its ultraviolet signature. The information it collected may help astrobiologists study the atmospheres of space objects.

On Nov. 13, 2009, Rosetta, a comet orbiter spacecraft commissioned by the European Space Agency swooped by Earth for its third and final gravity assist on the way to humankind’s first rendezvous to orbit and study a comet in great detail.

One of the instruments aboard Rosetta is the NASA-funded UV imaging spectrometer, dubbed Alice, which is designed to probe the composition of the comet’s atmosphere and surface. It will be the first UV spectrometer to study a comet up close. During the spacecraft’s recent Earth flyby, researchers successfully tested Alice’s performance by viewing the Earth’s UV appearance.

“It’s been more than five years since Rosetta was launched on its ten-year journey to comet 67P/Churyumov-Gerasimenko, and Alice is working well,” said instrument principal investigator Dr. Alan Stern, who is associate vice president of the Space Science and Engineering Division at Southwest Research Institute (SwRI). “As one can see from the spectra we obtained during this flyby of the Earth, the instrument is in focus and shows the main UV spectral emission of our home planet. These data give a nice indication of the scientifically rich value of UV spectroscopy for studying the atmospheres of objects in space. We’re looking forward to reaching the comet and exploring its mysteries.”

Dr. Paul Feldman, professor of physics and astronomy at The Johns Hopkins University, and an Alice co-investigator, has studied the Earth’s upper atmosphere from the early days of space studies. “Although the Earth’s UV emission spectrum was one of the first discoveries of the space age and has been studied by many orbiting spacecraft, the Rosetta flyby provides a unique view from which to test current models of the sun’s interaction with our atmosphere.”

SwRI also developed and will operate the NASA-funded Ion and Electron Sensor (IES) aboard Rosetta. The IES will simultaneously measure the flux of electrons and ions surrounding the comet over an energy range extending from the lower limits of detectability near 1 eV, up to 22,000 eV.

Thanks to an Earth gravity assist swing-by in November, Rosetta is now on a course to meet its cometary target in mid-2014. Before the spacecraft reaches its main target, it will explore a large asteroid called Lutetia in July. The Alice UV spectrometer will be one of the instruments mapping this ancient asteroid.

NASA’s Jet Propulsion Laboratory in Pasadena, Calif., manages the U.S. Rosetta project for NASA’s Science Mission Directorate.

For more information, visit: www.esa.int/esaMI/Rosetta