Cloud photos suggest that Jupiter is wet.

The Galileo probe that dropped into Jupiter's atmosphere in December, 1995, detected a smaller amount of water than scientists expected. However, researchers at California Institute of Technology, Pasadena, have new thundercloud photographs and a theory to suggest that the solar system's largest planet may be "wet" after all.

According to Andrew Ingersoll, professor of planetary science, the probe didn't find much water because it dropped into a cloud-free area of the Jovian atmosphere. Since water likely would be manifested in clouds, he thinks the probe might have detected the predicted amount of water had it fallen into another region. As it stands. the probe data suggest that water is about 10 times more scarce than most scientists once thought. "This was the most cloud-free area on the planet, so the probe went into an anomalous region. A low cloud abundance means that there's less of the condensable substances, including water."

Ingersoll and colleagues are offering photographic evidence to back up their assertion that water on Jupiter merely was hidden from the probe. A series of near-infrared images taken by the Galileo orbiter show several dozen thunderclouds to the northeast of the Great Red Spot. These round clouds jut about 20 miles above the cloud cover and are of similar diameter. The researchers are not sure yet whether the clouds are made of water, but they do know that the clouds are high and evolve rapidly, like terrestrial thunderstorms.

The theory Ingersoll developed jointly with graduate student Adam...