August 13, 2010 Last summer a massive mystery object struck Jupiter and disappeared into its opaque atmosphere. Now, research led by Shu Lin Li of Peking University in China has revealed that billions of years ago Jupiter’s core might have been vaporised in huge collision with a planet up to ten times the size of Earth. Computer simulations showed that the incoming rocky body flattened when it hit the gas giant’s atmosphere before drilling into the giant’s core with the energy of the collision vaporising much of the the planet's core. Jupiter, which is more than 120 times bigger than the Earth, has an extremely small core that weighs just two to 10 Earth masses, while Saturn's comes in at 15 to 30.
These vaporised heavy elements would then have mixed with the hydrogen and helium of the gas giant's atmosphere, leaving only a fraction of the gas giant's former core behind. This could explain not only why Jupiter's core is so small, but also why its atmosphere is richer in heavy elements compared with the sun, whose composition is thought to mirror that of the nebula that gave birth to the solar system's planets (arxiv.org/abs/1007.4722).
These vaporised heavy elements, reported New Scientist, would then have mixed with the hydrogen and helium of the gas giant’s atmosphere, leaving only a fraction of the gas giant’s former core behind, which could explain not only why Jupiter’s core is so small, but also why its atmosphere is richer in heavy elements compared with the Sun, the scientists said.
Study co-author Douglas Lin at the University of California, Santa Cruz, told New Scientist that the super-Earth might have grown into a gas giant itself one day if it had not collided with Jupiter.
“It may very well have been on its way to becoming a gas giant, but lost the race and got gobbled up.” Saturn has a similar overabundance of heavy elements in its atmosphere and the scientists believe this could also be due to impacts by rocky objects smaller than Earth that decelerated and broke up before they could reach Saturn’s core. Jupiter and Saturn are thought to have begun life as rocky worlds with the mass of at least a few Earths. Their gravity then pulled in gas from their birth nebula, giving them dense atmospheres.
“It’s an interesting explanation of why you might have a variety of core masses in giant planets,” said William Hubbard of the University of Arizona in Tucson. “It’s a very useful contribution.” The new findings help clarify the evidence that the solar system's birth was a violent and chaotic business, with perhaps five of its eight extant planets having suffered impacts by other planet-sized objects, and the rest by objects not much smaller. Giant collisions are thought to have spawned Earth's moon, blasted away the outer layers of Mercury, reshaped Mars's northern hemisphere and knocked Uranus onto its side. Smash-ups may also have led Neptune to acquire a moon and slowed Venus's spin rate.
Casey Kazan via New Scientist http://www.newscientist.com/article/mg20727733.600-jupiter-swallowed-a-superearth.html and http://www.indianexpress.com/news/jupiter-swallowed-planet-10-times-the-size-of-earth/659441/
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