Image: Jupiter
The New Horizons Long Range Reconnaissance Imager took this 2-millisecond exposure of Jupiter on Jan. 24, 2007. At right are the moons Io (bottom) and Ganymede.
By staff writer
updated 2/27/2007 7:33:41 PM ET 2007-02-28T00:33:41

Jupiter, the largest planet in the solar system, is about to welcome a robotic visitor.

NASA’s New Horizons probe will make its closest pass by the gas giant at about 12:45 a.m. EST (0545 GMT) Wednesday in a sort of cosmic stopover on its long trek to distant Pluto and the Kuiper Belt. The planetary flyby comes just 13 months after New Horizons’ launch, with the probe hurtling through space at about 47,000 miles per hour (75,639 kph) on what NASA is billing as its fastest mission to solar system’s edge.

“We have a very narrow window in space that we have to hit,” New Horizons principal investigator Alan Stern, of the Southwest Research Institute in Boulder, Colo., has said of the rendezvous. “It’s about 500 miles (804 kilometers) across and we have to hit it from 500 million miles (804 million kilometers) away, from the Earth.”

It’s the equivalent of shooting a skeet target in Baltimore, Md., from a firing range in Washington, said Stern.

At its closest approach, the New Horizons is expected to fly within 1.7 million miles (2.3 million kilometers) of Jupiter. The first data from that pass is expected to arrive at Earth via the Deep Space Network at around 12:00 p.m. EST (1700 GMT) Wednesday, officials at the Johns Hopkins University’s Applied Physics Laboratory, which is overseeing the mission for NASA, told

New Horizons is the first probe to visit Jupiter since NASA’s Galileo orbiter plunged into the gas giant’s atmosphere to end its 14-year mission in 2003. The Cassini orbiter, currently circling the planet Saturn, swung past Jupiter in December 2000.

New science awaits
Already, the New Horizons probe has returned new views and movies of Jupiter’s moons, though the interaction of the sun’s solar wind with the planet’s vast magnetosphere takes center stage for some researchers.

Jupiter has the largest magnetosphere in the solar system, with its trailing non-Sunward direction — known as the magnetotail — stretching out towards the orbit of Saturn. New Horizons instruments have already detected a dense region of solar wind known as a shock, which develop as a fast layer of solar wind particles compress a slower layer ahead like a snow plow.

“I think the most exciting part about the next few days is that we’ll see our closest measurements to Jupiter,” SwRI’s David McComas, principal investigator for New Horizon’s Solar Wind Around at Pluto instrument, told

New Horizons’ observations of Jupiter’s magnetic field will help researchers determine which processes – such as solar wind or planetary rotation – spawn auroras and other phenomena. The results will be compared tandem studies by the Hubble Space Telescope and other space and ground-based observatories, McComas said.

The Pluto-bound probe will also be the first spacecraft ever to fly down Jupiter’s magnetotail, a journey that could take anywhere between 45 and 70 days depending on how the magnetic field “flaps” as it extends from the gas giant planet, researchers said.

“It’s sort of like a windsock…because the solar wind doesn’t flow exactly radially outward,” McComas said of the magnetotail, which may extend anywhere between 1,000 and 1,500 times the radius of Jupiter. The planet’s radius spans about 43,495 miles (70,000 kilometers).

Spacecraft shakedown
New Horizons’ Jovian magnetosphere studies are part of no less than 700 separate observations planned during the Jupiter flyby, which serves as a shakedown period for the spacecraft’s seven instruments. The probe will also grab a gravitational boost from the planetary pass, shaving three years off its journey for a July 2015 Pluto rendezvous.

Slideshow: Month in Space: January 2014 “Here on the ground we aren't yet seeing much science data, but the engineering data we're getting shows the encounter is progressing nominally and the various observations are coming off right on schedule,” Stern wrote in Monday status update on the New Horizons mission website at JHUAPL.

New Horizons began studying Jupiter and its moons in earnest on Feb. 24, and is conducting between 15 and 20 observations each day, Stern said. On Monday, the spacecraft was due to map the surfaces of Jovian moons Ganymede and Europa, study the atmospheres of satellites Io and Callisto, as well as photograph Jupiter’s “Little Red Spot,” Io’s volcanic plumes and the gas giant planet’s faint rings, he added.

It takes about 45 minutes for a signal from New Horizons to reach Earth from Jupiter’s neighborhood, according to a mission description.

Much of New Horizons’ Jupiter flyby instructions have already been uploaded to the spacecraft since the probe will be out of contact with Earth while it studies the Jovian system.

Those instructions include an auto shutdown of the SWAP instrument in case Jupiter’s near magnetosphere proves too strong for the tool, which was designed primarily for the Pluto environment, McComas said. If that occurs, SWAP should restart automatically once New shortly after Horizons’ closest swing past Jupiter, he added.

“You work on these things for many years, designing and developing, going through a launch and getting the thing up in space,” McComas said. “It’s an extremely exciting time for my team and me.”

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