For only the second time in recent history, scientists have observed the results of an object plunging into the solar system's largest planet.
The object, thought to be an asteroid or comet, left a large dark bruise that can still be seen spreading over Jupiter's southern hemisphere, according to Leigh Fletcher, a planetary scientist at the Jet Propulsion Laboratory in La Canada-Flintridge.
"This is an incredible event," Fletcher said in an interview. The last time something like this happened was 15 years ago, when fragments of the Shoemaker-Levy comet plunged into the huge gaseous envelope that makes up most of the planet.
Scientists were able to follow all 20 or so fragments as they entered the outer atmosphere, made up mostly of hydrogen and helium.
This time, the object that hit the planet was not observed. The first announcement of a new scar on the planet's exterior came Sunday from amateur Australian astronomer Anthony Wesley.
As word spread, professional astronomers around the world turned their attention to the planet, which is so large it could hold 1,400 Earths. At its closest, Jupiter is about 390 million miles from Earth, four times as far as the Earth is from the sun.
Some of the sharpest observations came from the Keck II telescope in Hawaii. UC Berkeley astronomer Paul Kalas had previously requested viewing time on the telescope and used the opportunity Monday to confirm the amateur observation.
"We don't see other bright features along the same latitude, so this was most likely the result of a single asteroid, not a chain of fragments" as with Shoemaker-Levy, UC Berkeley astronomer Franck Marchis said in a statement.
The event could help scientists better understand the meteorology on Jupiter, Fletcher said. The scar was probably a result of the object disturbing high altitude aerosols, or dust particles, in the atmosphere.
When first analyzed, it was about the size of the Pacific Ocean. Fletcher said Tuesday that the bruise was growing and would probably continue to do so until fading away in a few days or weeks.
Even at its largest, the feature will probably remain a mere blot compared with the planet's Great Red Spot, a long-lasting storm that is twice the diameter of Earth.