91av

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’s 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—the region controlled by the
planet’s 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’s 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’s 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’s 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’s calling “hot
spots”, unlike anything seen on Earth. “Those field lines go way further out
than expected,” says Gladstone. “Something weird is happening.”

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