Thanks to keen-eyed amateur astronomer Anthony Wesley of Australia, the world became aware of a second giant impact on planet Jupiter within 15 years. The event occurred on July 19. Fifteen years earlier-almost to the day-20 fragments of Comet Shoemaker-Levy 9 smacked into Jupiter. The July 1994 event was televised around the world.
"I noticed a dark spot rotating into view in Jupiter's south polar region and started to get curious," Wesley told reporters about his recent discovery. "When first seen close to the limb, and in poor conditions, it was only a vaguely dark spot, I thought likely to be just a normal dark polar storm. However, as it rotated further into view, and the conditions improved, I suddenly realized that it wasn't just dark, it was black in all channels-meaning it was truly a black spot."
The impact blemish discovered by Wesley is big-very big; it's about the size of Earth's Pacific Ocean. Had the giant asteroid or comet that created this Jovian event collided with Earth, it would have been 1,000 greater in explosive power than the Tunguska comet airburst over the remote tundra of Siberia in 1908.
Other professional and amateur astro photographs of the impact site are being posted on the Internet almost weekly. The images show the atmospheric aftermath of the event as a spreading black ink spot. But what happened down below the Jovian clouds after such a cosmic wallop?
Jupiter's slushy "surface" is under titanic pressure; it is composed of a very weird liquid-metallic form of hydrogen. This "surface" (the term is used loosely by astronomers) lies deep beneath an increasingly dense and smoggy atmosphere composed of 90 percent hydrogen, 12 percent helium, along with methane, water, ammonia, silicon-based compounds, carbon, ethane, hydrogen sulfide, neon, oxygen, nitrogen, phosphine, and sulfur. With a lot of this "porridge" to plow through, there's probably no impact craters from either last month's event or the 1994 comet spectacle. Besides, where would you begin to look in Jupiter's "surface" environment?