Two distant galaxies provide new puzzles - 4c 41.17, B2 09021+34

Astronomers exploring the nature of galaxy formation and evolution have shed new light on two of the most distant galaxies known in the universe. Both bodies were initially identified by their unusually intense radio emissions, and both lie so far away from Earth that astronomers observe them as they appeared billions of years ago, when the universe was just 10 percent of its current age. Nonetheless, the galaxies sport several differences.

"They were startled by the light; it lit up the shuttle," says Murad. The plume of nitrix oxide created an intense blue-white glow. Then the orange halo along the shuttle's tail got much brighter for about 3 seconds as the nitric oxide settled back onto the shuttle surface and reacted with the oxygen that collided with the craft.Scientists then tried to reproduce the glow in their laboratories, but they got a different color than what shuttle astronauts saw outside their windows, says Murad. And for good reason, he adds: The researchers needed air filled with oxygen atoms, not the two-atom oxygen molecules found in air at Earth's surface. Also, since the shuttle orbits Earth at about 7.8 kilometers per second, the free-floating oxygen atoms that collide with the shuttle hit their target quite fast. "It's not easy to make a very fast neutral oxygen in the lab," Murad says.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.The Mars Observer will enter orbit, 248 miles above the Martian surface, on Aug. 24 (see p. 104). Once in orbit, the spacecraft will send back detailed pictures of geologic features such as the polar ice cap, where layers of dust surround icy deposits. These deposits "may reflect a much more arid period of Mars' past," says Bevan M. French, program scientist for the Mars Observer mission at NASA headquarters in Washington, D.C.

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.

Author: Ron Cowen