After a near five year journey, NASA's Juno spacecraft reached Jupiter. e
The poles of Jupiter glow in brilliant blues when viewed by scientists through ultraviolet filters, a swarm of energy similar to, but more powerful than Earth's Northern Lights.
Researchers understand little about how Jupiter's massive and powerful magnetic field triggers that constant aurora because the gaseous giant's size and distance from the sun make it so different from Earth. They believe the largest planet could offer lessons about how massive clouds of energized particles collapsed to form the solar system and other parts of the universe.
NASA's Juno spacecraft, which entered orbit around Jupiter on the Fourth of July, will give scientists their first close-up look at the auroras and the clouds of energetic particles swirling around the solar system's second-largest body after the sun. Researchers at the Johns Hopkins Applied Physics Laboratory in Laurel, who oversaw studies of Jupiter's magnetic field in past NASA missions, will again help lead that part of the exploration.
"We are traveling in regions no spacecraft has flown before, so we expect to see some surprises," said Barry Mauk, a project scientist at the lab who is lead investigator for Juno's Jupiter Energetic Particle Detector instrument, known as JEDI.
Juno is only the second spacecraft to orbit Jupiter, following Galileo's visit in the 1990s. NASA hopes the Juno mission can answer some big remaining questions about the planet. Half a dozen instruments on board will gather data not just on Jupiter's magnetic field, but on how much water exists on the planet, whether it has a solid core beneath its gaseous surface, and just what is going on within its famous red spot, which is shrinking.
The spacecraft won't get its first chance to make what are expected to be its most valuable observations until late August, when it swings within 3,000 miles of Jupiter's clouds in the closest approach of its elliptical, 53-day-long orbit.
"It's the end of the voyage, but it's the beginning of the science," said Michael Watkins, director of the NASA Jet Propulsion Laboratory in Southern California, on July 4 when Juno successfully completed its five-year, 1.8 billion-mile journey to Jupiter.
That NASA lab is in charge of the mission, the same role the Hopkins lab holds on the New Horizons mission that flew by Pluto last July.
As with New Horizons, the Juno mission is a broad effort, with key researchers coming from the Southwest Research Institute, the University of Hawaii, California Institute of Technology, the University of Colorado at Boulder, the Planetary Science Institute and the Hopkins lab.
Juno's instruments include JunoCam, slated to capture the first close-up images of Jupiter's poles, and a microwave radiometer that will map the planet's interior structure by detecting subtle gravitational tugs on the spacecraft. Several other instruments are using magnetometry, spectroscopy and an infrared camera to focus on the auroras.
The JEDI instrument will measure electrons and other charged particles streaming around Jupiter to learn how they interact with the planet's magnetic field.
Mauk and colleagues at the Laurel lab developed their proposal for JEDI in 2003 and 2004. They had experience with similar instruments on Galileo and both Voyager missions, which flew by Jupiter in 1979 on their way to the outer reaches of the solar system. They also employed similarly designed instruments on the New Horizons mission, to see how the "solar wind" of charged particles from the sun influence Pluto, and the Van Allen Probes, two spacecraft launched in 2012 to measure belts of radiation surrounding Earth.
"I love Jupiter," said Mauk, who started working at the Hopkins lab in 1982. "It's a great scientific target."
Jupiter differs dramatically from Earth. At more than 300 times Earth's mass, Jupiter's belts of radiation are about 1,000 times more intense than Earth's, Mauk said. And while activity in Earth's magnetic field comes from interactions with bursts of energy from the sun, Jupiter generates its own energy with its rotation and with material ejected from volcanoes on Io, one of its many moons.
With the JEDI instrument, the Hopkins scientists will zero in on an area near Jupiter's poles where the charged material speeds up before it bombards the planet's atmosphere, triggering the auroras.
Auroras occur when charged particles excite gases in an atmosphere, causing them to glow. While it is a temporary phenomenon on Earth tied to solar storms, it is constant on Jupiter.
"These auroras are very dramatic and among the most active I have ever seen," said Jonathan Nichols, a member of Juno's science team who studies auroras at the University of Leicester in the United Kingdom.
Some scientists believe the process that leads to the auroras is similar to one that caused a swirling mass of energy to organize into the solar system some 4.6 billion years ago, though that remains a controversial theory, Mauk said. Learning more about it could help humans better understand space, he said.
"We feel that's a very important general process operating throughout the universe," Mauk said.
Juno will orbit around Jupiter 37 times to learn as much as it can, traversing a treacherous environment with each trip. The high-energy electrons around Jupiter are a constant and penetrating barrage.
To withstand them, most of Juno's electronics are protected within a titanium vault that makes the spacecraft like "an armored tank," said Scott Bolton, principal investigator of the Juno mission at the Southwest Research Institute.
Though the spacecraft is designed to survive the bombardment, it ultimately is doomed by design.
So it doesn't disturb any of Jupiter's moons — such as the icy, but potentially habitable Europa, which NASA plans to explore in a future mission— it will crash onto Jupiter itself in February 2018.
Tribune Newspapers and the Associated Press contributed to this article.