Jupiter probe grabs solar-power record

While not as famed as the New Horizons spacecraft that visited Pluto last year, a plucky spacecraft called Juno has been on a mission since 2011 to visit Jupiter, seeking to peer beneath its cloud cover and reveal some of the secrets of the fifth rock from the sun.

Juno won't arrive at the Jovian skies until around July 4 of this year, but it made history Wednesday by becoming the spacecraft to travel farthest from Earth using only light from the sun.

Previous craft that have traveled this far in our solar system have used nuclear fuel to power their maneuvers, but Juno is a 100 percent solar operation. When it reached a distance of about 493 million miles (793 million kilometers) from the sun on Wednesday, it surpassed the record previously held by Rosetta and showed that long-distance operations from the sun are indeed possible, even though the sunlight out there is 25 times weaker than it is on Earth.

"While our massive solar arrays will be generating only 500 watts when we are at Jupiter, Juno is very efficiently designed, and it will be more than enough to get the job done," Rick Nybakken, Juno's project manager from NASA's Jet Propulsion Laboratory, said in a statement.

Juno has three 30-foot-long (9-meter) solar arrays spreading out from its center, and each is covered with 18,698 individual solar cells made from silicon and gallium arsenide. The craft weighs four tons (about 3.62 tonnes) and is the first probe specifically designed to operate on sunlight so far from the Sun itself.

"Prior to Juno, eight spacecraft have navigated the cold, harsh underlit realities of deep space as far out as Jupiter," NASA said. "All have used nuclear power sources to get their job done. Solar power is possible on Juno due to improved solar-cell performance, energy-efficient instruments and spacecraft, a mission design that can avoid Jupiter's shadow, and a polar orbit that minimizes the total radiation."

When Juno -- named for the wife of the mythical supreme god of the Roman pantheon, Jupiter -- reaches orbit around the planet that's most famous for its Great Red Spot, the craft will begin the first of 33 trips around Jupiter. It will get within 5,000 kilometers (about 3,000 miles) of the planet's gaseous cover and attempt to send back information about the magnetosphere and atmosphere, including just how deep the planet's colorful cloud features run. Jupiter has an intense magnetic field because hydrogen gas is compressed so much that it turns into a fluid known as metallic hydrogen, which acts like a metal that can conduct electricity.

This vigorous magnetic activity sparked as these particles shower down through the atmosphere also creates the brightest auroras in our solar system, something else Juno will observe.

"It is cool we got the record and that our dedicated team of engineers and scientists can chalk up another first in space exploration," said Scott Bolton, Juno principal investigator at the Southwest Research Institute in San Antonio. "But the best is yet to come. We are achieving these records and venturing so far out for a reason -- to better understand the biggest world in our solar system and thereby better understand where we came from."