Chemical collisions cause shuttle's halo - why orbiting spacecraft sometimes develop a golden glow

An experiment to test a 50-year-old theory of astrophysics has solved the myster of why orbiting spacecraft sometimes develop a golden glow.

The study also revealed an unsettling finding. The team detected what appears to be a bright red halo around B2 0902 34. If the halo is confirmed, it suggests that stars at the outskirts of the galaxy are redder, and possibly older, than those at the core -- a phenomenon never before observed."It's like looking at a roomful of babies ranging from 1 day to 1 year old," says Mark Dickinson of the University of California, Berkeley. "A small difference in age can make a big difference in appearance -- and in the case of galaxies, not all were born at the same time."In studying another distant radio galaxy, B2 0902 34, which lies only slightly closer to Earth, Dickinson and Peter R. Eisenhardt of the Jet Propulsion Laboratory in Pasadena, Calif., have solved an old puzzle. The researchers began their ground-based infrared study after astronomer Simon J. Lilly, now at the University of Toronto, reported that although the galaxy is observed soon after the birth of the universe, it has very red stars -- indicating that the stars are more than 1 billion years old (SN: 4/23/88, p.262). That finding spells trouble for most cosmology theories, which can't explain how a galaxy could have evolved so rapidly after the Big Bang.The halo along a satellit's leading edges results when nitric oxide combines with oxygen atoms to form nitrogen dioxide, reports Edmond Murad of the Philips Laboratory at the Hanscom Air Force Base in Massachusetts. After this reaction occurs, electrons in the molecules become temporarily excited and the molecules leave the shuttle surface, Murad and his colleagues explain in the Nov. 7 NATURE. Then, as the electrons return to their normal state, the molecules emit light, creating an aura that extends about 20 centimeters out from the shuttle surface.During last April's flight of the shuttle Discovery, Murad and his colleagues were testing whether accerated atoms or molecules can reach high enough speeds to become charged briefly and then release energy as they return to a neutral state. This phenomenon, called the critical ionization velocity, can help explain the formation of the solar system; it was first suggested by Hannes Alfven, a Nobel-winning plasma physicist.Neither the astronauts nor the ground-based researchers expected what they saw when they ejected nitrix oxide into space.Eisenhardt and Dickinson now report that Lilly's view of B2 0902 34 was colored by the red glow of ionized oxygen gas in the galaxy. They say that the stars at the center of the galaxy are actually bluer, and thus younger, than believed -- no more than 300 million years old. Indeed, B2 0902 34 could be a proto-galaxy, a galaxy caught in the act of formation, the researchers report in the Nov. 1 ASTROPHYSICAL JOURNAL LETTERS. In contrast to 4C 41.17, light from the galaxy is not aligned with its radio emissions, they note. In addition, B2 0902 34 has a somewhat younger star population and a blobby, less elongated shape.

Now that scientists know how the glow originates, Murad says, they should try to mount space-bound instruments to face away from the craft's leading edge to present these instruments from "seeing" the glow. Otherwise, they should adjust their measurements to account for any artifacts caused by the halo.

Author: Elizabeth Pennisi