It's nice to live in a solar system with an enormous gas giant making itself a big target, and absorbing some of the impacts that could possibly befall the inner solar system (although, theoretically Jupiter could also "bend" the trajectory of passing objects towards Earth too, and Jupiter didn't have the Dinosaurs back 65-million-years ago). On July 19th, an amateur astronomer by the name of Anthony Wesley noticed a dark spot on the south polar region of Jupiter. At the time it was unclear whether this was an impact or some sort of weather phenomenon.
New infrared images from NASA's Jet Propulsion Laboratory seem to provide evidence of an impact exactly 15 years after Jupiter was bombarded by the comet Shoemaker-Levy 9. Scientists are not sure what hit Jupiter (asteroid, rogue comet, monolith, etc.), but the resulting impact scar is big.
How big? The size of Earth.
From NASA:
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Following up on a tip by an amateur astronomer, Anthony Wesley of Australia, that a new dark "scar" had suddenly appeared on Jupiter, this morning between 3 and 9 a.m. PDT (6 a.m. and noon EDT) scientists at NASA's Jet Propulsion Laboratory in Pasadena, Calif., using NASA's Infrared Telescope Facility at the summit of Mauna Kea, Hawaii, gathered evidence indicating an impact.
New infrared images show the likely impact point was near the south polar region, with a visibly dark "scar" and bright upwelling particles in the upper atmosphere detected in near-infrared wavelengths, and a warming of the upper troposphere with possible extra emission from ammonia gas detected at mid-infrared wavelengths... This image was taken at 1.65 microns, a wavelength sensitive to sunlight reflected from high in Jupiter's atmosphere, and it shows both the bright center of the scar (bottom left) and the debris to its northwest (upper left). "It could be the impact of a comet, but we don't know for sure yet," said Orton. "It's been a whirlwind of a day, and this on the anniversary of the Shoemaker-Levy 9 and Apollo anniversaries is amazing."
According to New Scientist, the object that hit Jupiter could have been a huge "block of ice from somewhere in Jupiter's neighborhood, or a wandering comet that was too faint for astronomers to detect before the impact."
"Our first image showed a really bright object right where that black scar was, and immediately we knew this was an impact," Orton says. "There's no natural phenomenon that creates a black spot and bright particles like that." Supporting evidence came from measurements of Jupiter's temperature. Thermal images also showed a bright spot where the impact took place, meaning the impact warmed up the lower atmosphere in that area.
The researchers have also found hints of higher-than-normal amounts of ammonia in the upper atmosphere. Extra ammonia had been churned up by the previous Shoemaker-Levy comet impact.