Saturn: finding the hots ... and tracking a recent storm.

Using an infrared camera, astronomers have imaged several "hot spots" never before detected on Saturn. Richard L. Baron and Tobias C. Owen of the University of Hawaii in Honolulu say the infrared-bright regions likely represent holes on the thick, heat-absorbing layer of clouds believed to blanket Saturn's lower atmosphere. The holes, they say, permit heat from the planet's interior to leak out into space.

Ordinary photographs do not reveal the hot regions, since the shorter wavelengths associated with visible light cannot penetrate Saturn's dense upper atmosphere, Owen notes. And researchers who previously searched fo rhot spots with infrared telescopes failed to find them, he adds, because the scientists used broadband filters that permit a wide range of near-infrared wavelengths to reach their detectors. Such studies record the bright, overall infrared glow from the planet, which can wash out the hot spots because they radiate only at a few infrared wavelengths, Owen and Baron discovered.

To hunt for hot spots, the astronomers attached a camera known as ProtoCAM to NASA's Infrared Telescope atop Mauna Kea in Hawaii. Instead of recording photons on film, the camera relies on an infrared array -- a group of infrared-sensitive picture elements on a semiconductor chip (SN: 11/16/91, p.312) -- to make an image. Baronand Owen used a series of special filters that allowed the array to view narrow bands of light between the near-infrared wavelengths of 4.9 and 5.3 microns.

Observing Saturn on July 8 and 9, the researchers discovered an intermittent ribbon of hot spots that stretches at least halfway around the planet at about 15 degrees N. Another infrared-bright region, partly hidden by Saturn's rings during the July study, hints that a similar ribbon exists at 15 degrees S, Owen says. the study also revealed two fainter and thinner infrared-bright zones closer to the planet's north pole, which the researchers speculate may represent unidentified structures in the lower cloud layer other rhan thermal holes.

Owen notes that part of the mechanism responsible for hot spots on Saturn resembles that which underlies similar features on Jupiter. Borth planets have thick, cloudy atmospheres. On Saturn, atmospheric helium succumbs to gravity, falling toward the planet's interior and releasing heat in the process. Holes in low-lying clouds then act like a camera with its shutter open, allowing the helium's heat, detected as infrared light, to exit from the atmosphere unimpeded.

Owen cites two key differences between the two planets' hot spots: Researchers can view Jupiter's with broadband filters, he says, because Jupiter apparently contains lower concentrations of heat-absorbing phosphine gas than Saturn. And leftover heat from the formation of Jupiter, rather than infalling helium, likely fuels the Jovian emissions.

. . . and tracking a recent storm

Comparing ground-based images with those taken by the Hubble Space Telescope, astronomers have found that a single atmospheric disturbance triggered Saturn's "white spot" -- the storm that erupted in September 1990. Reta F. Beebe and Lyle Huber of New Mexico State University in Las Cruces and their colleagues used the images to trace the movement of a closed eddy that accompanied the storm (SN: 11/24/90, p.325).