Europa’s Juice Mission launches to Jupiter and its moons

Jupiter, king of the solar system, gets a new robot visitor.

The Jupiter Icy Moons Explorer, or Juice, launched Friday morning from the Guyana Space Center in Kourou, French Guiana, on the northeast coast of South America. The original launch, scheduled for Thursday, was postponed after lightning was detected near the launch site.

On Friday, the weather improved and the spacecraft, aboard an Ariane 5 rocket, lifted off flawlessly. Half an hour later, Juice separated from the rocket’s second stage and began its long journey.

Jupiter, the largest planet to orbit the sun, is fascinating in its own right, but its huge moons are the ultimate reward. Some of them are pieces of icy rock that can hide life-sustaining oceans beneath their surface. Juice, from the European Space Agency, or ESA, wants to closely study three of Jupiter’s satellites: Callisto, Europa, and Ganymede.

“This is one of the most exciting missions we’ve ever flown in the solar system, by far the most complex,” said Josef Aschbacher, the head of ESA.

Weighing six tons, the European spacecraft carries 10 advanced scientific instruments to study the moons and capture images. Jupiter is not the mission’s primary target. Instead, it aims to explore Ganymede, the largest moon in the solar system, and two other moons, Europa and Callisto.

But reaching Jupiter will take Juice more than eight years, with a series of swings or gravity assists past Venus, Mars and Earth to give the spacecraft the push it needs to enter Jupiter’s orbit in July 2031.

When Juice finally reaches Jupiter, it will repeatedly fly past the three moons in a looping orbit, staying outside the giant planet’s dangerous radiation belts as it collects data. A total of 35 flybys are planned as the spacecraft searches for magnetic signals and other evidence to confirm the presence and size of oceans sloshing beneath the moons’ surface. It will also track how the outsides of the moons move in response to Jupiter’s gravitational pull, possibly influenced by the subsurface oceans.

The moon that may be most promising in the search for life is Europa. Astronomers think the ocean is in direct contact with a rocky bedrock, which could provide food and energy for life if hydrothermal vents burst upward. Juice will conduct two flybys of Europe.

The spacecraft will also perform 21 flybys of Callisto, which may also have a salty ocean but is believed to be less capable of supporting life.

But the Juice mission’s primary goal is the study of Ganymede, a moon so large that it is larger than the planet Mercury. The spacecraft’s path around the Jovian system should allow the spacecraft to be captured in orbit around Ganymede in December 2034 — the first spacecraft to orbit a moon in the outer solar system. Starting at about 3,100 miles above the surface, the spacecraft’s altitude will gradually decrease to just over 300 miles by 2035 — and perhaps lower, fuel permitting.

“Once we have enough propellant, meaning we’ve had a good trip to Jupiter without too much trouble, we’ll reduce the orbit to” an altitude of about 150 miles, said Giuseppe Sarri, the project manager for Juice at ESA.

Orbiting Ganymede allows scientists to understand the Moon’s features in an intricate way. It is the only moon in the solar system known to have its own magnetic field, possibly from a liquid iron core like our own planet’s. “If you stand on the surface of Ganymede and you have a compass needle, it points to the north pole like on Earth,” said Michele Dougherty of Imperial College London, who directs the magnetometer instrument on Juice. “We want to understand why.”

Juice should be able to discern Ganymede’s internal structure, including the size and expanse of the ocean. It should even be able to measure the salinity of the ocean due to minerals circulating in it that can sustain life. “We’re trying to understand where the salts came from,” Dr. Dougherty up.

Ganymede’s ocean is significantly different from Europa’s, but may still be habitable.

“For habitability you need liquid water, a source of heat and organic materials,” said Dr. Dougherty. “If we confirm or deny those three things, we did what we said we were going to do.”

The mission will end with an emergency landing on Ganymede’s surface in late 2035, unless a discovery is made during the mission that suggests it could contaminate the moon’s ocean.

What other missions will study Jupiter?

Juice isn’t the only mission exploring Jupiter and its moons.

Juno, a NASA mission, has been orbiting Jupiter since 2016. The focus has been on the planet itself rather than its moons, though it has recently completed several close flybys of Europa and Ganymede and will fly past volcanic Io soon.

But Juice is also expected to be whisked to Jupiter by another new NASA mission, Europa Clipper, launching in October 2024. It is scheduled to arrive at the Jupiter system in April 2030, thanks to its more powerful launch vehicle, a SpaceX Falcon. Heavy missile. But there is no competition; the two missions are meant to work together.

“There will be two spacecraft looking at Jupiter and its moons at the same time,” said Dr. Ashbacher. “There’s a lot of science to be gleaned from that.”

The two missions were born in 2008 in response to exciting results from NASA’s Galileo spacecraftwhich orbited Jupiter from 1995 to 2003.

“Galileo found this very intriguing magnetic signal that suggested there was a conductive layer of ice under the shell of Europa,” says Louise Prockter of the Johns Hopkins Applied Physics Laboratory, who is part of the Europa Clipper team.

Scientists now think this was a sign of a global ocean that encompassed the interior of Europe.

Observations by the Hubble Space Telescope in 2018 suggest that Europa may occasionally spout its ocean in plumes through cracks in its icy shell, which is at least 10 miles (16 kilometers) thick. This could be a new way to directly study the ocean and look for signs of life as Clipper skims over the lunar surface, sometimes as low as about 15 miles.

“We could potentially fly through a plume,” said Dr. Prockter.

The results from both Juice and Clipper will reveal whether a landing on a moon of Jupiter on a future mission, likely to Europe, should be attempted to look for life directly in the ocean, something NASA has suggested. Such a mission could be two decades from now, but its scientific value is immense. Dr. Aschbacher said Europe was interested in something similar.

“We discussed an example of a return mission from one of the icy moons,” he said, which would bring material back to Earth for further study. “What we learn from Juice will be extremely important input for that.”

For now, the spotlight is on Juice’s, the first of a new era of spacecraft specifically designed to hunt alien worlds on oceans. “I can’t wait,” Dr. Dougherty said. “This is the next step.”