New Horizons flew by Jupiter in 2007, capturing images and data that provided new insights. It observed lightning on Jupiter near both poles, unlike on Earth where lightning concentrates near the equator. It also witnessed an eruption of the Tvashtar volcano on Io and found pollution from Io's volcanoes has reached Europa. As it flew through Jupiter's magnetotail, New Horizons detected pulses of energetic particles that flow along the tail in sync with Jupiter's rotation and every few days as plasma blobs are fed down.

1. SPECIALSECTION
INTRODUCTION
New Horizons
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Grand Tour at Jupiter
TRAVELING OUT TO THE FARTHEST REACHES OF THE SOLAR SYSTEM, TO PLUTO AND
the Kuiper belt where it will arrive in 2015, the New Horizons probe has to CONTENTS
endure a long and mostly uneventful journey. But luckily there are some spec-
tacular sights along the way. On 28 February 2007, New Horizons flew past Perspective
Jupiter, where it used the gas giant’s gravity to slingshot it to even greater speeds 216 New Surprises in the Largest
and also test its instruments in flight. New Horizons’ transit took it to unvisited Magnetosphere of Our Solar System
areas of the planet’s spacescape. The papers in this special issue record how the N. Krupp
probe witnessed lightning and aurorae in Jupiter’s atmosphere, volcanic erup-
tions on the moon Io, and the pulsing of Jupiter’s magnetosphere, a cocoon of Reports
charged particles that swathes the entire system. 217 Diverse Plasma Populations and
On Earth, although seen planetwide, the most powerful thunderstorms concen- Structures in Jupiter’s Magnetotail
D. J. McComas et al.
trate near the equator and in the tropics. Not so on Jupiter. Lightning flashed near
both poles as well as elsewhere, suggesting that convective electrical storms bub- 220 Energetic Particles in the Jovian
ble up everywhere in Jupiter’s atmosphere because of global heat imbalances. Magnetotail
R. L. McNutt Jr. et al.
Nighttime auroral glows, on the other hand, were not as widespread as expected.
Skirting the giant planet, New Horizons also flew by Jupiter’s rings and 223 Jupiter Cloud Composition,
attendant moons, big and small. Surprisingly, no moonlets smaller than a kilo- Stratification, Convection, and Wave
Motion: A View from New Horizons
meter in size were seen in Jupiter’s faint rings, a puzzle if they are built from the
D. C. Reuter et al.
debris of shattered moons. Rubble also clumps together in locations favored by
gravity resonances with larger moons. 226 Polar Lightning and Decadal-Scale
Cloud Variability on Jupiter
An eruption of the Tvashtar volcano on the satellite Io was caught in the act,
K. H. Baines et al.
allowing the mechanics of the sulfurous plume and the lava temperature to be
measured. Pollution from Io’s volcanoes has even reached the shores of Europa, 229 Jupiter’s Nightside Airglow and Aurora
G. R. Gladstone et al.
an icy moon that may harbor oceans beneath its frozen surface. Io’s volcanic
emissions feed extra sulfur and oxygen ions into a vast particle cloud that circles 232 Clump Detections and Limits on Moons
the entire Jupiter system, held in place by the planet’s strong magnetic field. in Jupiter’s Ring System
M. R. Showalter et al.
Behind the planet, it is pulled into a magnetic shadow billions of kilometers
long, streaming away from the Sun as the solar wind deflects around Jupiter. 234 New Horizons Mapping of Europa and
Ganymede
CREDIT: PAM ENGEBRETSON AND JEFF MOORE (MONTAGE)
Acting like a giant pipe, this magnetic tail drains half a metric ton of charged
W. M. Grundy et al.
particles out of the jovian system each second. New Horizons’ route took it
down the magnetotail, to regions unexplored by earlier Galileo or Voyager mis- 237 Io’s Atmospheric Response to Eclipse:
sions (see the Perspective on p. 216). Pulses of energetic particles flow along the UV Aurorae Observations
K. D. Retherford et al.
tail in synchrony with Jupiter’s 10-hour rotation rate and also every few days as
plasma blobs are fed down the tube. 240 Io Volcanism Seen by New Horizons: A
With Pluto still in its sights, New Horizons’ snapshots show that Jupiter inhab- Major Eruption of the Tvashtar Volcano
J. R. Spencer et al.
its an active landscape, experiencing storms, the pumping of the magnetosphere,
and volcanic ash falls. A pity then that it is the last time we will visit Jupiter until
the Juno mission in 2016. So sit back, enjoy these views, and think of New Hori-
zons as it races along the solar system’s back roads to an even stranger destination.
– JOANNE BAKER
www.sciencemag.org SCIENCE VOL 318 12 OCTOBER 2007 215
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