A U.S. spacecraft has taken the closest images of Jupiter since the Galileo probe perished in a programmed dive into the huge planet's atmosphere four years ago. The spacecraft's destination is icy, distant Pluto, but the U.S. space agency NASA wanted to fly close to Jupiter on the way out to get a scientific update and a speed boost. VOA's David McAlary reports.

New Horizons spacecraft

More than 13 months after its launch, NASA's New Horizons spacecraft has made its closest pass to Jupiter on its 10-year voyage to Pluto. The head of NASA's science directorate and chief investigator for the mission, Alan Stern, says the flyby has been eagerly awaited.

"Between the demise of Galileo with the end of its very successful mission in 2003 and the arrival of the Juno Jupiter orbiter that we are all looking forward to in 2016, this is the only train going this way," said Alan Stern.

Jupiter's Little Red Spot

New Horizons has been taking pictures of Jupiter since January and will continue to dispatch them through June, but the close pass more than two million kilometers away is giving astronomers another detailed look at the gas giant, its rings, and its four biggest moons.

A mission scientist from the Southwest Research Institute in Boulder, Colorado, John Spencer, spoke of the goals before Wednesday's Jupiter pass.

"We very carefully tailored our observations so we will be not repeating things that have have been done by the other seven missions that have already been to Jupiter," said John Spencer. "Sometimes we are just looking for changes."

Jupiter flyby trajectory

The observations have included Jupiter's auroras and its giant red spot, a swirling centuries-old storm larger than Earth. New Horizons' advanced instruments have also peered at the planet's rings in an effort to find more tiny moons. In addition, it studied the surface composition of the big moons Gannymede; Callisto; Io, which has a volcano; and Europa, which is thought to have a liquid water ocean under a shell of ice.

The spacecraft will also become the first to take a trip down the long tail of Jupiter's magnetosphere, a wide stream of charged particles extending tens of millions of kilometers.

Alan Stern says the observations are intended as practice for the duties New Horizons faces at Pluto when it arrives in 2015.

"We have designed this particular flyby to be a stress test on our spacecraft to work out the kinks so that at Pluto, we do not learn a thing about our spacecraft, we have worked out those kinks at Jupiter, putting our spacecraft through 700 different observations," he said.

These observations are only one reason for the visit to Jupiter. The pass also lets the planet's strong gravity sling it away, providing a 14,000 - kilometer per hour speed boost. This cuts the spacecraft's flight time to Pluto by three years.

After the Jupiter encounter, New Horizons' electronics will become dormant for much of its cruise. Mission controllers will shut off all but the most critical systems and check in once a year to test those systems, calibrate instruments, and correct the course if needed.