The voyage of NASA's Pluto-bound New Horizons
spacecraft through the Jupiter system
earlier this year has provided a bird's-eye view of a
dynamic planet that has changed since the last
close-up looks by NASA spacecraft.
New Horizons passed Jupiter on Feb. 28, riding the
planet's gravity to boost its speed and shave
three years off its trip to Pluto. Designed, built and
operated at the Johns Hopkins University Applied
Physics Laboratory, New Horizons was the eighth
spacecraft to visit Jupiter, but a combination of
trajectory, timing and technology allowed it to explore
details no probe had seen before, such as
lightning near the planet's poles, the life cycle of fresh
ammonia clouds, boulder-size clumps speeding
through the planet's faint rings, the structure inside
volcanic eruptions on its moon Io and the path of
charged particles traversing the previously unexplored
length of the planet's long magnetic tail.
"The Jupiter encounter was successful beyond our
wildest dreams," said New Horizons principal
investigator Alan Stern, of NASA Headquarters, Washington,
D.C. "Not only did it prove out our
spacecraft and put it on course to reach Pluto in 2015, it
was a chance for us to take sophisticated
instruments to places in the Jovian system where other
spacecraft couldn't go, and to return
important data that adds tremendously to our understanding
of the solar system's largest planet and
its moons, rings and atmosphere."
The New Horizons team presented its latest and most
detailed analyses of that data on Oct. 9
at the American Astronomical Society's Division for
Planetary Sciences meeting in Orlando, Fla., and in
a special section of the Oct. 12 issue of the journal
Science. The section includes nine technical papers
written by New Horizons team members and collaborators.
From January through June, New Horizons' seven science
instruments made more than 700
separate observations of the Jovian system — twice
the activity planned at Pluto — with most of them
coming in the eight days around closest approach to
Jupiter.
"We carefully selected observations that complemented
previous missions so that we could
focus on outstanding scientific issues that needed further
investigation," said New Horizons Jupiter
science team leader Jeff Moore, of NASA Ames Research
Center, Moffett Field, Calif. "The Jupiter
system is constantly changing, and New Horizons was in the
right place at the right time to see some
exciting developments."
Jovian weather was high on the list, as New Horizons'
visible light, infrared and ultraviolet
remote-sensing instruments probed Jupiter's atmosphere for
data on cloud structure and composition.
They saw clouds form from ammonia welling up from the lower
atmosphere and heat-induced lightning
strikes in the polar regions — the first polar
lightning ever observed beyond Earth — demonstrating
that
heat moves through water clouds at virtually all latitudes
across Jupiter. They made the most detailed
size and speed measurements yet of "waves" that run the
width of the planet and indicate violent
storm activity below. Additionally, New Horizons snapped
the first close-up images of the Little Red
Spot, a nascent storm about half the size of Jupiter's
Great Red Spot and about 70 percent of Earth's
diameter, gathering new information on storm dynamics.
Under a range of lighting and viewing angles, New
Horizons also captured the clearest images
ever of the tenuous Jovian ring system. Scientists spotted
clumps of debris that may indicate a
recent impact inside the rings, or some more exotic
phenomenon, and movies made from New Horizons
images offer an unprecedented look at ring dynamics, with
the tiny inner moons Metis and Adrastea
shepherding the materials around the rings. A search for
smaller moons inside the rings — and possible
new sources of the dusty material — found no bodies
wider than a kilometer.
Investigations of Jupiter's four largest moons focused
on the closest one, Io, whose active
volcanoes blast tons of material into the Jovian
magnetosphere (and beyond). New Horizons spied 11
volcanic plumes of varying size, three of which were seen
for the first time, and one — a spectacular
200-mile-high eruption rising above the volcano Tvashtar
— that offered an unprecedented opportunity
to trace the structure and motion of the plume as it
condensed at high altitude and fell back to the
moon's surface. In addition, New Horizons spotted the
infrared glow from at least 36 Io volcanoes,
and measured lava temperatures up to 1,900 degrees
Fahrenheit, similar to many terrestrial volcanoes.
New Horizons' global map of Io's surface backs the
moon's status as the solar system's most
active body, showing more than 20 geological changes since
the Galileo Jupiter orbiter provided the
last close-up look, in 2001. The remote imagers also kept
watch on Io in the darkness of Jupiter's
shadow, noting mysterious glowing gas clouds above dozens
of volcanoes. Scientists suspect that this
gas helps to resupply Io's atmosphere.
New Horizons' flight down Jupiter's magnetotail gave
it an unprecedented look at the vast
region dominated by the planet's strong magnetic field.
Looking specifically at the fluxes of charged
particles that flow hundreds of millions of miles beyond
the giant planet, the New Horizons particle
detectors saw evidence that tons of material from Io's
volcanoes move down the tail in large, dense,
slow-moving blobs. By analyzing the observed variations in
particle fluxes over a wide range of
energies and scales, New Horizons scientists are exploring
how the volcanic gases from Io are ionized,
trapped and energized by Jupiter's magnetic field, then
ultimately ejected from the system.
New Horizons lifted off from Cape Canaveral Air Force
Station, Fla., in January 2006. The
fastest spacecraft ever launched, it needed just 13 months
to reach Jupiter. New Horizons is now
about halfway between the orbits of Jupiter and Saturn,
more than 743 million miles from Earth. It
will fly past Pluto and its moons in July 2015 before
heading deeper into the Kuiper belt of icy rocky
objects on the planetary frontier.
New Horizons is the first mission in NASA's New
Frontiers Program of medium-class spacecraft
exploration projects. APL manages the mission for NASA's
Science Mission Directorate.