Mystery shrouds origins of giant planet

 作者:赵枞捧     |      日期:2019-03-07 10:13:07
By Charles Seife THE “suicide note” left behind by a space probe has presented astronomers with a puzzle: where did Jupiter come from? The dying breaths of the Galileo atmospheric probe hint that the planet might have wandered towards the Sun after forming on the fringes of the Solar System. In 1995, the Galileo mission dropped a probe into the Jovian atmosphere. A mass spectrometer on board returned data on the composition of the atmosphere before the probe was crushed by pressures of 20 atmospheres. If Jupiter had formed from colliding comets, as many planetary physicists believe, then the levels of argon and other volatile elements in its atmosphere should be roughly the same as those observed in comets. However, the probe measurements reveal that they are not the same, says Tobias Owen, a physicist at the University of Hawaii. “Argon is as abundant relative to hydrogen as carbon and sulphur,” he says. “It was expected to be much less abundant.” Krypton and xenon, too, are present at higher levels than expected. “The pattern in the Jupiter data is not what is seen in comets,” agrees Kevin Zahnle of NASA’s Ames Research Center in Moffett Field, California. “It’s very interesting, because it was thought that comets were the building blocks.” Although Zahnle admits that the data analysis is very difficult and potentially error-prone, he says that if the findings are correct, the implications are important. One possibility is that Jupiter formed in a cold region much farther away from the Sun, allowing the young planet to trap volatile gases. The planet may then have migrated inwards to its current position. Another possibility is that Jupiter formed from material that was more primitive than anyone realised. Owen says: