Origin of Water on Jupiter Discovered: Comet Smashed into Planet

Water has been observed in Jupiter's stratosphere before. Now, though, researchers may have found what brought the liquid to the planet in the first place. A new study proposes that the Shoemaker-Levy 9 comet impact on Jupiter nearly 20 years ago is the culprit.

In July 1994, a comet slammed into the giant planet and left visible scars on the Jovian disk for weeks. The event itself excited astronomers at the time; it was the first, direct observation of an extraterrestrial collision in the solar system.

The comet didn't happen on the planet by "chance," though. SL9 was orbiting Jupiter for quite some time before actually hitting the planet. It was first discovered by David Levy and Carolyn and Eugene M. Shoemaker in 1993. At the time, it was the first ever comet recorded orbiting a planet instead of the sun.

The comet itself was composed of 21 fragments, and orbital studies revealed that it had passed within Jupiter's Roche limit in July 1992. Inside this limit, the planet's tidal forces are powerful enough to disintegrate a body held together by its own gravity; this helped explain why the comet had broken into so many fragments. The study of the space object also revealed that the comet's orbit was due to pass within Jupiter in July 1994, which meant that it would smash into the planet.

While the physical scars remained for weeks after the impact, the chemical scars lasted even longer. Emission from water vapor was observed during the fireball phase of the meteor's impact--the point at which it became a bright streak across Jupiter's atmosphere. Yet it was difficult to assess exactly how this vapor would modify Jupiter's atmosphere in the long term.

In 1997, though, researchers detected water vapor in the giant planet's atmosphere. They predicted that it could be caused by the comet, but they weren't able to make any firm predictions; there were other sources of water available, such as interplanetary dust particles or asteroid collisions. Now, though, they have been able to link back the water to the comet.

Using the ESA Herschel Space Observatory, the scientists were able to map the abundance of water vs. latitude and altitude in Jupiter's stratosphere. The data, in fact, showed a clear north-south asymmetry in the distribution of water, with more in the south. This, in turn, indicates that about 95 percent of the water currently observed on the massive planet comes from the comet.

The findings could have implications not only for how water originated on Jupiter, but also for how it originated on Earth. Similar comet strikes could have helped supply our atmosphere with water and, in turn, created the water in our oceans.

The findings are published in the journal Astronomy & Astrophysics.