A curious "hot spot" near Jupiter's north pole pumps out flashes of x-rays, space scientists report. The x-rays are most likely produced by ions crashing into the planet's atmosphere, but the spot's surprising location has researchers wondering where the ions come from.
For 2 decades satellite observations have shown that Jupiter emits x-rays from somewhere near its poles. Researchers reasoned that the x-rays are produced when oxygen and sulfur ions plunge into the planet's atmosphere and capture electrons. Until now, they believed the ions came from Jupiter's magnetosphere, the region in which the planet's magnetic field is strong enough to deflect the "solar wind," a stream of particles emitted by the sun. Specifically, the ions were thought to originate in the inner and middle portions of the magnetosphere, which stretch to roughly 2 million kilometers above Jupiter's surface.
But this theory has taken a serious hit now that a team has studied Jupiter with the Chandra X-ray Observatory, a satellite that is able to pinpoint the source of the x-rays. Randy Gladstone of the Southwest Research Institute in San Antonio, Texas, and colleagues expected to see x-rays coming from a ring around each pole. That's because ions spiral along Jupiter's magnetic field lines, and the lines that loop out to 2 million kilometers pierce the planet's surface at latitudes well away from the poles. However, when Gladstone and colleagues watched Jupiter during one complete 10-hour rotation in December 2000, they found that most of the x-rays were shining from a single pulsing spot close to the north pole. The field lines that point to the spot loop out 7 million kilometers to the wispy edge of Jupiter's magnetosphere, the researchers report in the 28 February issue of Nature.
The observation leaves space scientists wondering where the torrent of particles originates, says Tom Hill, a space physicist at Rice University in Houston. "If it's coming from that far out, it probably cannot be magnetospheric ions, because there aren't enough of them out there." The ions might leak in from the solar wind, Hill says. But Alex Dessler, a space physicist at the University of Arizona, Tucson, says the same area of the planet also produces unusual radio signals, flares of ultraviolet light, and high levels of infrared radiation and even seems to be correlated with a patch in Jupiter's magnetosphere that pumps out high-energy electrons. Dessler says that all these signs might point to a single poorly understood connection between the farthest reaches of the magnetosphere and features of the magnetic field near Jupiter's surface.