Images reveal stormy collision on Jupiter.

The stock market may still take another nosedive, but on Jupiter the crash of '98 is already history. Several years after astronomers first had evidence that two neighboring hurricanes in Jupiter's southern hemisphere were drawing closer together (SN: 8/16/97, p. 10T), the storms have collided.

The impact has forged a single vortex that has the same oval shape as its predecessors but is slightly larger and moves significantly faster. Although astronomers did not witness the collision--the merger apparently occurred in February, when Jupiter was hidden behind the sun--a variety of before and after images are helping to flesh out the story.

The giant storms, or anticyclones, known as BC and DE, had persisted for 58 years at a latitude of 33 [degrees] S. Pictures taken Jan. 17 at the Pic du Midi Observatory in Bagneres-de-Bigorre, France, showed them close together but distinct. NASA's Infrared Telescope Facility atop Hawaii's Mauna Kea recorded images on March 27, after Jupiter had emerged from behind the sun, showing but a single oval. In a June 17 circular of the International Astronomical Union, a U.S.-French team reported that BC and DE had merged. The researchers dubbed the new storm BE.

Some scientists, however, cautioned that the two storms might not have actually joined forces. Instead, one of them might simply have become too faint for ground-based telescopes to detect.

Images taken with the sharp eye of the Hubble Space Telescope on July 16 confirmed that a merger had indeed taken place, says Amy A. Simon of New Mexico State University in Las Cruces. "We just wanted to make to make sure, without a doubt, that [the other storm] was gone," she says.

The Hubble images reveal that BE is moving eastward at 2.5 meters per second. At 12,500 kilometers long and 8,400 km wide, the storm is second in size only to Jupiter's Great Red Spot. By comparing the data to vortex models, Simon and Reta F. Beebe, also of New Mexico State, hope to deduce the water content at the storm site, which determines the temperature and pressure across the vortex.

It remains unclear, says Simon, how the storms managed to collide despite being separated by a vortex rotating in the opposite direction. That vortex appears unchanged, even though one of the storms must have plowed through it to merge with the other. A third anticyclone, known as FA, that traveled along with BC and DE persists with no visible changes.

Another puzzle, notes Glenn S. Orton of NASA's Jet Propulsion Laboratory in Pasadena, Calif., is that the new storm lacks a dark ring like those that encircled BC and DE. The rings indicated that gas rising and cooling from the center of the storms had fallen back at the edges. A cloud layer may be covering the new storm's ring, Orton suggests.