Next stop for NASA: Jupiter.
With the space shuttle retired, the agency’s marquee missions now feature robots, not astronauts. And so on Friday morning, the agency is set to launch a $1.1 billion probe that will give the solar system’s largest planet a good, long look after a looping five-year journey of 1.7 billion miles.
Juno, a four-ton, solar-powered craft, will peer deep below Jupiter’s swirling clouds when it arrives in July 2016, seeking clues to the giant planet’s formation, searching for a hard core and mapping Jupiter’s intense magnetic field and radiation belt.
Juno will even listen for lightning amid Jupiter’s raging storms and gather unprecedented views of the planet’s sparkling auroras.
Planetary scientists say Jupiter was the first planet in the solar system to form, about 4.5 billion years ago. As a great cloud of hydrogen and helium gas coalesced, it spun into a giant ball about 1,300 times larger than Earth. But the ingredient list for this gas giant remains incomplete, its deep structure unknown.
“We don’t know if there’s a core of heavy elements in the middle or if it’s just gas all the way down,” said the mission’s chief scientist, Scott Bolton of the Southwest Research Institute in San Antonio.
To find out, scientists will use Juno — the entire craft — as a gravity probe. As Juno repeatedly zooms past Jupiter, ground stations on Earth will detect the tiny changes in the craft’s velocity. When Juno passes an especially dense region, it will speed up a smidge, tugged by stronger gravity. “If Jupiter is really massive in the middle, it will be clear from this map of the gravity field,” Bolton said.
At the same time, Juno’s microwave detector will peer about 300 miles beneath the top of Jupiter’s colorful surface, mapping the planet’s deep clouds while searching for water and, by proxy, oxygen.
Oxygen is the third-most-abundant element in the universe — after hydrogen and helium — but previous missions have failed to detect much of it inside Jupiter. “It’s the water we’re really after,” Owen said. “That will be very important” for testing theories of how Jupiter — and the other planets — formed.
Owen said that because Jupiter has changed very little since its formation, piecing together its composition will be like looking back in time to the beginning of the solar system.
Other instruments on Juno will map Jupiter’s magnetic field — by far the strongest in the solar system — and probe its stunning auroras, which, like those on Earth, girdle Jupiter’s north and south poles. Jupiter’s auroras are “truly spectacular,” said mission scientist Jack Connerney of NASA’s Goddard Space Flight Center in Greenbelt, but their source is unknown.
Jupiter is the biggest of the planets, and so it’s fitting that Juno enjoys its own list of superlatives. After swinging past Earth for a speed boost in 2013, Juno will be flung outward at 160,000 mph, making it the fastest man-made object in history.
Juno will dive closer to Jupiter — within 3,100 miles of the surface on each of its 30 planned orbits — than any previous spacecraft.
Juno is also the first sun-powered craft to visit the outer system. Three bus-length solar panels will provide the electricity for Juno’s instruments and communications systems. Previous missions to Jupiter, Saturn and beyond employed electric generators powered by radioactive materials. But advances in solar panel efficiency led to their inclusion on the Jupiter mission.
And Juno will become the first craft to orbit Jupiter pole-to-pole, which will allow the craft to map every strip of Jupiter as the planet rotates. “We’re basically casting a net of observations around the entire planet,” Bolton said.
But it will be a hostile ride for the 66-foot-wide craft, which is “armored like a tank” to withstand Jupiter’s blistering radiation belt, Bolton said. Deep in the heart of Juno lies a 500-pound titanium vault that shields sensitive electronics. The looping, leisurely path of Juno’s orbits — which will take 11 Earth days — will also provide some protection, sending the craft under the most intense portions of the radiation field.
Still, after a year in orbit, Juno will have absorbed a huge dose of radiation. “It’s going to fry eventually,” Connerney said.
If Juno arrives at Jupiter on schedule — July 4, 2016 — it will become the eighth NASA craft to visit the planet. Pioneer 10 was the first, zooming by in 1973, followed by five other probes that glimpsed the fifth planet from the sun before heading deeper into space.
Only one other craft has orbited Jupiter. NASA’s Galileo probe arrived in 1995 and surveyed the gas giant until 2003, when operators plunged the craft into the planet.
Juno will meet a similar fate — a destruction prescribed by international rules meant to protect any body in the solar system with more than a minuscule chance of harboring life. According to NASA, three of Jupiter’s moons — but not Jupiter itself — likely carry frozen water and so qualify for such protection: Europa, Ganymede and Callisto.
To prevent any possible Earthly contamination from reaching their surfaces, after an Earth year of intensely scrutinizing Jupiter, Juno’s operators will steer the windmill-like probe into the huge planet’s clouds, where intense pressure will squeeze it to oblivion.