Star Points for September 2009 by Curtis Roelle Jupiter, an Enabler of Life on Earth On July 19 Australian amateur astronomer Anthony Wesley became the first person to notice a strange, new, dark marking on the planet Jupiter. It was later determined that this was a tell-tale bruise left in Jupiter's atmosphere caused by an impact with either an asteroid or a comet. And it was not the first time in recent years that Jupiter had been struck by such an object. Previously, almost fifteen years ago to the day, Jupiter was bombarded with fragments from Comet Shoemaker-Levy 9 (SL9). Astronomers concluded that SL9 had been "captured" by Jupiter and had been orbiting the planet for 20-30 years prior to impact. Then, during a close encounter in 1992, the tidal forces of massive Jupiter's gravitational influence caused the comet to break into pieces. Two years later, more than 20 large chunks of the comet rained down on Jupiter. It was as if Jupiter had chewed up, and then swallowed, the comet's every crumb. Although astronomers knew about Jupiter's ability to "bully" comets and asteroids smaller than itself, the events of 1994 and 2009 were the first time in history that anyone had witnessed it in action. These bodies impacted Jupiter because its gravity had robbed them of energy, slowing them down, and causing them to come crashing in. Jupiter can do the opposite as well. Its gravity can accelerate other bodies, giving them enough speed to cast them, in slingshot fashion, out of the solar system, never to return again. Jupiter's useful service of vacuuming up or ejecting comets and other bodies careening into the solar system from the far reaches has been credited with protecting life on Earth by shielding it from calamitous impacts. The geologic history of Earth suggests that certain epochs of mass extinction have occurred in the past. Evidence has been found linking some of these epochs of mass extinction to impacts with interloping comets or asteroids. For example, the discovery of a layer of iridium in rock layers here on Earth provided evidence to link the extinction of the dinosaurs to the impact of an extraterrestrial body. The discovery and dating of a large crater, now known as "Chicxulub," in the sea along the coastline of Mexico's Yucatan Peninsula, was the smoking gun of the dinosaur-killing event 65 million years ago. Without Jupiter's immense gravitational influence, it is much more likely that small celestial bodies would continue to collide with the Earth, causing similar extinctions. The more common such events would be, the less likely that life could have an opportunity to recover and evolve further. Jupiter keeps the solar system tidy, sweeping away the dirt and gravel, although every once in a while a chunk of something slips through, wreaking great havoc. Although the chance that an extinction event will occur in any given year is small, the result would be catastrophic. Not only would the impact itself cause destruction and death, the effect on the weather, from the amount of dust excavated and cast into the upper atmosphere, would be long-lasting. The blocking of sunlight would reduce the photosynthesis of plants, and the lack of plants for food would have a negative effect on other life farther up the food chain. The human race shouldn't thank only its lucky stars for its continued survival. We should also be thanking our lucky planets, too, especially Jupiter.