Exploring an accelerating universe.

Throughout his remarkable career, the late cosmologist David N. Schramm sought to unite the very tiny--the study of elementary particles--with the very big--the origins of the universe. At a recent conference honoring Schramm, NASA Administrator Daniel S. Goldin, along with representatives of the National Science Foundation and the Department of Energy, urged scientists to develop space missions that would explore the profound connections between these two realms.

One such example has just been put on the drawing board. Saul Perlmutter of the Lawrence Berkeley (Calif.) Laboratory proposes a mission that he says could determine unequivocally whether the universe is expanding at an increasing rate, as some recent observations have suggested.

Perlmutter leads one of two teams studying distant type la supernovas, a class of exploded stars. These supernovas appear dimmer than would be expected if the universe's rate of expansion was constant or slowing down (SN: 12/19 & 26/98, p. 392). However, researchers have only studied about 100 supernovas and have not ruled out other explanations. For example, distant supernovas might be intrinsically fainter than nearby ones.

"We're really trying to nail down the supernova story and make sure that all possible variables are covered," he says.

A space-based telescope with a huge field of view--one square degree, or twice the apparent size of the full moon--could within a year hunt down and extensively study 2,000 type la supernovas, Perlmutter said at the Schramm memorial meeting, held in late May at the Fermi National Accelerator Laboratory in Batavia, Ill.

Crucial to the proposed mission, which Perlmutter calls SNAPSAT (Supernova/Acceleration Probe Satellite), are the size and sensitivity of its light detectors--large mosaics of solid-state sensors known as charge-coupled devices. Such detectors are now common, but Lawrence Berkeley scientists have figured out a way to stitch together several hundred of the largest ones, allowing for an unusually wide field of view, Perlmutter says. They have also devised a way to manufacture the detectors at less than a fourth their current cost, he adds.

"It's a great idea," says Wendy L. Freedman of the Carnegie Observatories in Pasadena, Calif., who notes that such a mission would avoid the vicissitudes of weather and the atmospheric blurring that plague ground-based studies. Perlmutter notes that if the universe is indeed accelerating, SNAPSAT may shed light on the nature of the "funny energy" that is driving the cosmos to speed up its expansion