Telescope finds tiny moon of Jupiter Jan. 7, 1610, was a red-letter day for as-

tronomy. That evening, as Jupiter rose above the domes of Padua’s majestic San Antonio Basilica, Galileo Galilei took his usual window seat on the top floor of his house. Peering through a small, hand- crafted telescope, Galileo discovered three small objects hovering near the planet. A week later, he reported a fourth body “wandering around Jupiter, as do Venus and Mercury around the sun.” Galileo was the first to recognize moons orbiting Jupiter.

Those four moons-the only ones big enough for Galileo to see-have 1,000 times the girth of the latest Jovian find. Astronomers last week reported Jupiter’s 17th known moon, an object some 5 kilo- meters wide. If confirmed, it would rank as the tiniest satellite identified for any planet, as well as the first Jovian moon discovered in 25 years.

The astronomers made their find with a 79-year-old telescope, just 36 inches in diameter, atop Kitt Peak in Arizona. Known as Spacewatch, the telescope scans the solar system for asteroids and comets. Spacewatch researcher James V. Scotti of the University of Arizona in Tuc- son arranged for the telescope to exam- ine a region of sky near Jupiter for sever- al nights last October. Scotti knew Jupiter was near its closest approach to Earth,

Jupiter’s new moon {in box).

making the time ideal for finding any undiscovered moons.

Yet he and his colleagues didn’t notice that one of the newly observed objects, which appeared to be in the main aster- oid belt between the orbits of Mars and Jupiter, was moving too slowly to be an asteroid. Scotti followed the standard procedure of forwarding the data to the International Astronomical Union’s (lAU) Minor Planet Center at the Smithsonian Astrophysical Observatory in Cambridge, Mass. Researchers there designated the object an asteroid, 1999 UX,,.

On July 18, an astronomer at the cen-

ter, Tim Spahr, used the 1999 Spacewatch measurements to test a new computer program designed to identify slow-mov- ing objects. It revealed 1999 UX,, in addi- tional Spacewatch images over a 16-day span last fall.

When Spahr tried to construct an orbit around the sun for 1999 UX,,, he couldn’t get a satisfactory fit. He wondered if the body might instead be circling Jupiter.

Calculations by the center’s director, Brian G. Marsden, and associate director, Gareth V. Williams, revealed that a Jovian orbit fit all the Spacewatch observations. Williams’ analysis showed that the object isn’t one of Jupiter’s 16 previously known moons. He calculates that the moon be- longs to a group of moons that lies some 24 million km from Jupiter, takes about 2 years to orbit the planet, and moves in a direction opposite to the other Jovian satellites.

Researchers at Spacewatch and the cen- ter announced their findings in a July 20 circular of the MU. Even with this moon, Jupiter’s retinue would still lag behind that of Saturn, with 18 known moons, and Uranus, which has 20.

With Jupiter now rising in the morning sky, large telescopes can now observe the 17th moon, in the morning sky. The Galileo spacecraft, which has toured Jupiter since 1995, may attempt to view the object and obtain spectra next Feb- ruary, when it comes within 12 million km of the satellite. -R. Cowen

Newfound gas is greenhouse powerhouse Scientists have detected in the atmc-

sphere a gas that traps heat more effec- tively than any other previously found there. Laboratory measurements show that, pound-for-pound, it absorbs about 18,000 times as much infrared radiation as carbon dioxide does.

The researchers find the gas, trifluc- romethyl sulfur pentafluoride (SFJF,), only at trace levels-about 0.12 parts per trillion in 1999-in the atmosphere, but their analysis shows that concentrations are rising at about 6 percent per year. The research, led by scientists at the Uni- versity of East Anglia in Norwich, Eng- land, is reported in the July 28 SCIENCE.

The newly detected gas is chemically similar to sulfur hexafluoride (SF,)-an- other strong absorber of solar radiation- which manufacturers put into gas-insulat- ed electrical switches, transformers, and other high-voltage equipment. SF, is also commonly used in magnesium smelting and the manufacture of semiconductors (SN: 7/15/00, p. 45).

Samples of air trapped in Antarctic ice show that SF5CF3 first began to appear in the atmosphere in the late 1960s, says William T. Sturges, lead author of the re- port. Concentrations of this gas have risen in tandem with those of SF,;, which

suggests a link between the two, he adds. Sturges and his colleagues say they

don’t believe that SF,CF:, is a manufac- turing byproduct because they haven’t been able to detect it in freshly made batches of SF,. Instead, the researchers surmise that the newly identified gas forms when SF,: breaks down inside high-voltage equipment and then reacts with perfluorinated carbon compounds commonly included there.

If the gas does indeed form inside the high-voltage equipment, Sturges says, substantial amounts of SF,CF, may al- ready be present in those devices.

Although the sources of SFJF, haven’t been identified, they are almost certainly not natural processes, Sturges says. T h e e fore, he’s optimistic that scientists can de- velop ways to curtail the emissions.

“It would behoove us to discover the source of this gas so that we can make better-informed decisions about what to do,” agrees Stephen A. Montzka, an atmospheric research chemist at the National Oceanic and Atmospheric Ad- ministration in Boulder, Colo.

Measurements on air samples collect- ed by high-altitude balloons launched from France in 1999 and Sweden in 1997 suggest that SFSCF:, doesn’t easily break

down into compounds that are more be- nign, Sturges says. Instead, the data sug- gest that the gas slowly builds up in the atmosphere. By drawing an analogy with nitrous oxide measurements, the re- searchers estimate that SFsCF, has a life- time of at least several hundred years.

The newfound gas joins a growing group of atmospheric trace compounds, many humanmade, that strongly absorb infrared radiation and threaten to exac- erbate the greenhouse effect. Sturges and his colleagues recently reported the presence of fluoroform (CHF,), and he says he’s convinced that other green- house gases in low concentrations are yet to be identified. The researchers are now calculating the collective warming ef- fect of these compounds, which Sturges says will be significant in terms of the Ky- oto protocol. That international agree- ment seeks to substantially reduce green- house-gas emissions from industrial nations by the year 2012.

There’s clearly a need to identify long-lived, potent greenhouse gases well before their industrial production and use becomes widespread, Sturges told SciENcE NEWS. “Together, these gas- es are not very abundant, but they can make a difference,” he says. “[SFsCF3] is not a present-day threat, but it‘s one to be vigilant of.” -S. Perkins

70 SCIENCE NEWS, VOL. 158 JULY 29,2000