Juno spacecraft braves the unknown at Jupiter to enter orbit

NASA's Juno spacecraft, spinning once every 12 seconds for stability, fired its main engine for more than 35 minutes Monday to brake into orbit around Jupiter. Credit: NASA/JPL-Caltech
NASA’s Juno spacecraft, spinning once every 12 seconds for stability, fired its main engine for more than 35 minutes Monday to brake into orbit around Jupiter. Credit: NASA/JPL-Caltech

Setting up post at the king of planets, NASA’s Juno spacecraft fired its main engine for 35 minutes Tuesday, steering into orbit around Jupiter to peer inside the gas giant and give scientists a better idea of how the Solar System took shape 4.6 billion years ago.

Spinning on its axis once every 12 seconds, the probe’s British-built rocket thruster ignited and slowed down Juno just enough to be snared by Jupiter’s strong gravity field into a looping, 53-day-long orbit.

Confirmation of the burn’s successful conclusion reached Earth at 0353 GMT via a radio tone broadcast by Juno, prompting applause and smiles inside the control room at NASA’s Jet Propulsion Laboratory in Pasadena, California.

“All stations… we have the tone for burn cutoff on delta-v,” a ground controller said over a radio loop. “Welcome to Jupiter.”

Powered by three solar panels arranged in a propeller-like pattern around Juno’s main body, the Jupiter orbiter wrapped up a five-year, 2.8-billion-kilometre (1.7-billion-mile) trip with Monday’s automated rendezvous with the Solar System’s biggest planet.

“Tonight, through tones, Juno sang to us, and it was a song of perfection,” said Rick Nybakken, Juno’s project manager at JPL. “After a 1.7-billion-mile journey, we hit our burn target within one second.”

The record-setting journey made Juno the farthest spacecraft from the sun to ever rely on solar power, and Monday’s maneuver made the $1.1 billion mission the second to ever orbit Jupiter.

Built by Lockheed Martin, Juno braved harsh radiation and dodged tiny particles of ice and dust from Jupiter’s thin rings on its approach Monday, speeding over the planet’s north pole and flying within 4,667 kilometres (2,900 miles) of the gaseous world’s churning cloud tops, closer than any previous mission not on a trajectory to plunge into the atmosphere.

With Jupiter’s gravity tugging it in, the spacecraft became one of the fastest space probes in history Monday, topping out at more than 58 kilometres per second (36 miles per second), during the arrival sequence.

The unknowns going into Juno’s Fourth of July encounter with Jupiter gave many scientists caution, and mission managers highlighted the risks ahead of the spacecraft’s date with destiny.

But Juno performed like a champ Monday, according to initial data radioed back to Earth.

“We just did the hardest thing NASA’s ever done! That’s my claim,” shouted Scott Bolton, Juno’s principal investigator from the Southwest Research Institute in San Antonio, in excitement moments after the spacecraft’s was verified in orbit.

Members of the Juno team celebrate after confirming the spacecraft entered orbit around Jupiter on Monday. Credit: NASA/Aubrey Gemignani
Members of the Juno team celebrate after confirming the spacecraft entered orbit around Jupiter on Monday. Credit: NASA/Aubrey Gemignani

Bolton leads an international science team seeking to use Juno’s instruments to peel back the layers on Jupiter, revealing the dynamics of its deep atmosphere and the structure of its central core for the first time.

“Now the fun begins — the science,” Bolton said.

Named for the wife of Jupiter in Roman mythology, a figure who could see through the cloak of clouds kept by the chief deity, Juno will reveal the gaseous world’s poles in detail for the first time, peer beneath Jupiter’s clouds with a microwave radiometer, and search for evidence of a solid core.

Earlier missions left open questions about the inner workings of Jupiter, and instead focused on taking pictures and surveying the planet’s many moons.

Steven Levin, Juno’s project scientist at JPL, said the most important measurement the mission will collect, in his opinion, is the amount of water inside Jupiter.

“Just by measuring that one number, the amount of water inside Jupiter, we can learn a lot about how Jupiter formed, and that teaches us not just about Jupiter, but about the whole solar system,” Levin said.

Leading theories hold that Jupiter formed after the sun, but before the rest of the worlds in the solar system, so learning about the early history of Jupiter is a bridge to learning how the rest of the planets were born.

A suite sensors on Juno will also study the origin of Jupiter’s intense magnetic field and auroras. Scientists will use the data to infer information about the planet’s deep interior and measure the environment around Jupiter.

“Oddly enough, Jupiter’s interior is quite a mystery to us, and that’s ironic because it’s made up of two of the simplest and and most abundant elements in universe, and those are hydrogen and helium,” said Jack Connerney, Juno’s deputy principal investigator and head of the magnetometer team at Goddard Space Flight Center. “But the problem is it’s under such great pressure in that environment that it behaves in very mysterious ways.”

“The whole univerise is almost all hydrogen and helium,” Bolton said. “But when we look closely at the composition of Jupiter, we learn that it has an enrichment of what scientists call heavy elements — all the elements beyond helium in mass, so the carbon, the nitrogen, the sulphur, the noble gases — Jupiter is enriched with these elements compared to the Sun. We don’t know exactly how that happened, but we know it’s really important.”

Jupiter has a magnetic field 20,000 times more powerful than Earth’s, Connerney said, trapping high-energy electrons along magnetic field lines and giving the planet the most hazardous environment in the Solar System other than the Sun.

“Jupiter is a planet on steroids,” Bolton said. “Everything about it is extreme.”

It has more than twice the mass of all the other matter in the Solar System besides the Sun. Jupiter has a diameter of 139,822 kilometres (86,881 miles) and is 318 times more massive than Earth, containing 1,321 times the volume of our home planet.

“When you go to study Jupiter and learn about how it formed, what you’re really learning about is the history of those volatiles, those elements that eventually made us,” Bolton said. “We’re learning about what state and how they might have been distributed early in the solar system, which will fold into models about how you not only make Jupiter, but how you eventually make the other planets.”

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