COBE: seeking traces of the beginning.

COBE: Seeking traces of the beginning

Scheduled for launch as early as Nov. 9 a satellite called the Cosmic Background Explorer (COBE) will search for whatever faint glimmer remains from the birth of the universe. Looking back billions of years before the appearance of Earth, COBE's planned year-long survey will focus on neither planets nor stars but on the Big Bang that cosmologists widely believe led to both.

The long-awaited Hubble Space Telescope, due to orbit Earth next March, will look at some of the oldest stars in the sky. But even they are latecomers by COBE's standards. "Hubble has to wait until the lights come on. COBE begins before the lights come on," says Lennard A. Fisk, NASA's associate administrator for space science and applications.

COBE carries three instruments. One, the Differential Microwave Radiometer, primarily seeks to determine whether the Big Bang was equally intense in all directions. If it finds the brightness of the cosmic background radiation patchy rather than smooth, scientists will face the task of identifying as yet-unknown "seeds" around which formed galaxies, galactic clusters, and clusters of galactic clusters. If the device measures equal brightness in all directions, the question of how these systems could have condensed since the Big Bank will become even more difficult to answer.

Liquid helium will cool COBE's two other instruments to only 1.6[degrees]C above absolute zero, making them sensitive to extremely faint heat emissions. The Far-Infrared Absolute Spectrophotometer, designed to determine the spectrum of the background radiation produced by the Big Bang, will survey the entire sky twice during the mission. Many astrophysicists reason that such a spectrum should be smooth and uniform, showing no significant releases of energy between the Big Bang and galaxy formation.

Variations from this spectrum could indicate the unexpected presence in the early universe of energy sources such as the annihilation of antimatter and explosions of supermassive objects that might have driven turbulence capable of triggering galactic formation. NASA officials rate the spectrophotometer's sensitivity as 100 times greater than that yet achieved by equivalent ground-based and balloon-borne infrared instruments. Researchers hope the data will essentially answer the question, "How bright was the big Bang?"

Also supercooled is the Diffuse Infrared Background Experiment. This one is assigned to the "new" stuff. To survey distant primordial galaxies and other celestial objects that formed after the Big Bang, it will weed out the total glow of our own galaxy--the collective radiance of billions of stars and other celestial objects within the Milky Way--from the rest of the universe. This will be a matter of accounting for the many kinds of known objects whose emissions will get in the way, as well as for Earth's motion within the interplanetary dust permeating our own solar system.

After COBE has identified and subtracted all known sources and any newly discovered ones, a faint and uniform residual signal may remain. The COBE team hopes this will prove to be the long-sought light of primordial galaxies, produced by some of the young universe's first big beacons.