NASA’s Juno spacecraft poised for ‘tantalizing’ data on Jupiter

Scientists say the mission could provide a gateway to unlock clues about the early formation of the solar system

By Kenneth Chang  /  NY Times News Service, NEW YORK

Sat, Jul 09, 2016 - Page 9

On Tuesday, hours after arriving on Jupiter, NASA’s Juno spacecraft had already been flung by the planet’s immense gravity onto the outward leg of its orbit.

That was the plan, of course. The spacecraft arrived on Monday night, diving through intense barrages of radiation and reaching 209,215kph as it passed 4,668km above Jupiter’s cloud tops.

Juno fired its main engine for 35 minutes, slowing it down just enough to be captured by Jupiter’s gravity.

“Everything executed just like we designed it to,” Juno project manager Rick Nybakken said in an interview. “It’s doing very well.”

As the spacecraft sped around Jupiter, the team at NASA spent much of Tuesday eliminating its wobbles.

By design, Juno cartwheels as it flies, which helps stabilize the spacecraft. The firing of the main engine can induce slight wobbles because of fuel left in the tanks.

The mission controllers can compensate by adjusting the positions of Juno’s three 9m-long solar panels, much as a skater can adjust her spinning speed by pulling in her arms or extending them.

Once the realignment is complete, the spacecraft will resume communications via its main antenna.

This brief lull gives scientists and engineers time to catch their breath after Juno’s suspenseful, but flawless arrival and before work begins to peer deep inside Jupiter.

Mission scientists will be looking for clues that might tell how the planets came together in the early history of the solar system.

“It’s the gateway to being that much closer to getting this really tantalizing science data,” Nybakken said.

It took five years for Juno to travel this far on its US$1.1 billion mission, and the spacecraft is scheduled to make 37 orbits around Jupiter over the next 20 months.

The science instruments, which were turned off for the arrival, were to be restarted on Thursday.

However, after its close encounter with the gas giant on Monday night, Juno is already too far away to make precise measurements: As of Tuesday afternoon, it was 1.13 million kilometers from Jupiter and speeding away at 48,280kph.

Juno will swing back around on a 53-day highly elliptical orbit and make another close pass over Jupiter on Aug. 27, the first time the camera and science instruments will gather eagerly awaited data.

Juno will fire its engine again on Oct. 19 to move to a 14-day orbit, when the science measurements begin in earnest.

Slight discrepancies in Juno’s radio signals will reveal minute variations in Jupiter’s gravitational field.

From that data, scientists hope to figure out if there is a rocky core inside the gas giant.

Magnetic fields measurements will give hints of the churning electric currents deep inside the planet. Microwave emissions will tell researchers about the temperatures and the concentrations of any water.

All that information will yield clues about whether Jupiter formed where it is now or farther out in the solar system, then migrated to its current orbit. Because Jupiter is the biggest planet and formed first, the information will also tell scientists about the cosmic leftovers that coalesced into the solar system’s other planets.

Juno’s data will also provide insights into the meteorology of Jupiter’s colorful bands of clouds and will help explain how the Great Red Spot has persisted for centuries — and perhaps why it is now shrinking.

On Monday night, NASA scientists released a video of images taken by Juno as it approached Jupiter, showing the dance of the planet’s four large moons: Io, Europa, Ganymede and Callisto.

Even these early photographs hint at scientific mysteries.

Callisto, for instance, is unexpectedly dim.

“We don’t know why,” Juno principal investigator Scott Bolton said during a news conference after Juno’s arrival. “We’ll have to figure it out.”

With a different vantage on a polar orbit, the spacecraft’s cameras are likely to add to the number of Jupiter’s known moons, now 67.

“Juno is really searching for some hints about our beginnings, how everything started,” Bolton said. “But these secrets are pretty well guarded by Jupiter.”

The assault of radiation each time Juno zooms past Jupiter will take its toll on the electronics. As the mission progresses, the spacecraft is to pass through increasingly violent parts of the radiation belts.

On Feb. 20, 2018, during the 37th orbit, Juno is to make a suicidal dive into Jupiter, ending the mission the same way that Galileo, NASA’s previous Jupiter orbiter, was disposed of in 2003.

That will ensure that there is no possibility of Juno’s crashing into Europa and contaminating it with microbial hitchhikers from Earth.

The moon is regarded as one of the likelier places for life elsewhere in the solar system.

The Juno mission so far is the latest in a string of successes for NASA, including the flyby of Pluto a year ago by the New Horizons spacecraft and the landing of the car-size Curiosity rover on Mars in 2012.