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Boston

SOMETHING strange is happening on Jupiter. Its magnetic field extends
hundreds of times further out into space than previously thought, creating
auroras that make the Earth鈥檚 northern lights seem feeble in comparison.

Jupiter is the giant of the Solar System, more than a thousand times as
massive as Earth. In January 2001, the combined power of the Cassini and Galileo
space probes, the Chandra X-ray telescope and the Hubble Space Telescope were
all trained on the Jovian magnetosphere鈥攖he region controlled by the
planet鈥檚 magnetic field.

Magnetic field lines fan out from a planet like the lines of iron filings
from the poles of a bar magnet. Auroras are caused by ions zipping along these
lines, so researchers can use the location of auroras to track how far out into
space the planet鈥檚 magnetic field lines can trap ions from the solar wind.

Randy Gladstone and his colleagues at the Southwest Research Institute in San
Antonio, Texas, used Chandra to map the Jovian auroras. Earth鈥檚 northern lights
shine only with visible light, but the more violent Jovian auroras emit
X-rays.

The X-ray auroras on Jupiter extend surprisingly far from the planet鈥檚 poles,
showing that field lines reach far out into space. Gladstone also found that the
auroras pulsated regularly every 45 minutes in certain places he鈥檚 calling 鈥渉ot
spots鈥�, unlike anything seen on Earth. 鈥淭hose field lines go way further out
than expected,鈥� says Gladstone. 鈥淪omething weird is happening.鈥�

Theorists have trouble explaining why Jupiter鈥檚 magnetosphere is so much more
powerful than Earth鈥檚, even allowing for the planet鈥檚 greater size. 鈥淛upiter鈥檚
magnetosphere is like Earth鈥檚 on steroids,鈥� says Thomas Hill, who works on the
theory of magnetospheres at Rice University in Houston, Texas.