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The largest mission to Jupiter will search for life in oceans buried under ice

The European Space Agency’s ‘Juice’ probe is set to begin an eight-year journey to one of the most hostile environments in the Solar System to explore some of the moons of the giant planet

Surface of Europa, Jupiter's moon, taken by the European probe Galileo in the 1990s.
Surface of Europa, Jupiter's moon, taken by the European probe Galileo in the 1990s.ESA

Jupiter is so large and violent that many astronomers compare it to a mother star around which the planets orbit, or in this case, its more than 80 moons. Among them are the four that Galileo Galilei discovered in 1610 and whose mere existence helped to overthrow the theory that the Earth is the center of the universe: Callisto, one of the oldest bodies in the Solar System; Io, the one with the most volcanoes; Europa and Ganymede, the largest moon in the entire Solar System. Jupiter is at an average distance from the Sun of 778 million kilometers, five times further than Earth, but even so it is thought that within several of these satellites there are vast oceans of liquid water able to sustain life.

“A few years ago I would have said that it was unthinkable to find living beings in this environment, but now I know that we are close to achieving it,” acknowledges the Spanish astrophysicist Luisa María Lara in a telephone interview on the way to the European spaceport in French Guiana, where the Juice mission of the European Space Agency (ESA) is scheduled to launch on Thursday.

In 2007, when this mission was approved, Lara was 40 years old. Now she is 56 and, in eight years, when the spaceship reaches Jupiter, she will have one year left of active work life. “I will have a year to enjoy the new data and then I will retire,” says Lara, who has participated in the development of two of the 10 scientific instruments on the mission. The Juice mission is set to end in 2035, when the ship will crash into the icy surface of Ganymede, leaving a crater about 6.5 feet (two meters) in diameter.

“This mission is a monster,” sums up Nicolas Altobelli, a 46-year-old Frenchman and head of the mission’s scientific activities, which will be directed from the ESA center in Villanueva de la Cañada, on the outskirts of Madrid, Spain. The solar arrays have a surface area similar to that of a medium-sized apartment — 85 square meters or over 900 square feet — the largest ever created for an interplanetary mission. The total mass of the ship is over six tons, more than half of it just for the propellant needed to carry out all its scientific maneuvers, especially the orbital jumps between Callisto, Europa and Ganymede. The ship is so large and heavy that to send it from Europe to Kourou in French Guiana, one of the largest planes in the world had to be used, the Antonov 124, operated, despite the war, by a company from Ukraine.

Juice is an acronym for Jupiter Icy Moons Explorer. It has to take off on Thursday at precisely 9:15 a.m. local time. This will allow it to optimize the fuel, carrying out a complex interplanetary choreography in which it will gain speed using the force of gravity of the Earth, the Moon and Venus, in a total of four flybys and eight years of travel. The journey will take so long that the probe’s computer programming can be updated from Earth so that it does not become obsolete, explains Altobelli, scientific leader of a €1.6 billion ($1.7 billion) project involving some 2,000 people.

The vast majority of the 5,000 known exoplanets beyond our solar system are worlds like Jupiter. They probably also have several icy moons around them. The discoveries that this probe can make on the Galilean moons, Altobelli argues, could change the way we think about these worlds and the possibility of life on them. “One of the usual requirements is for there to be oxygen, but this gas was not necessary for the appearance of life on early Earth,” notes the astrophysicist. “However, you do need oxygen for complex life to appear like it is on Earth today.”

The presence of liquid water is an essential condition for life to exist, but it is not enough. There must also be a rocky bottom with the essential elements for any form of life, which planetary scientists call CHNOPS: carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. The first moon to be visited by Juice, Callisto, may harbor an ocean in contact with the bedrock, so it could meet those requirements. But confirming that there is life down there is a huge challenge for human technology, since the liquid water is probably about 155 miles (250 km) under the ice. Despite this, this moon is interesting on its own, points out Claire Vallat, mission scientist. “It is one of the oldest bodies in the Solar System; it has witnessed its entire history and we hardly know anything about its internal structure”, she highlights. The instruments on board the ship will make it possible to map the surface and prospect its interior thanks to visible light, laser and radar cameras, among others.

Then Juice will focus on the favorite in the bets in terms of providing a habitable environment, Europa, which the probe will fly over twice at an altitude of about 248 miles (400 km). “This moon should have many more craters than we are seeing and we believe that something is erasing them,” says Vallat.

This satellite has ice volcanoes similar to those on Earth, but made entirely of frozen water of different densities and temperatures. “Temperate ice” flows are believed to periodically renew the surface, which would explain the mystery. On this moon the ocean is about 62 miles (100 km) underground, which makes it entirely unreachable, but in this case there is indirect evidence that there are geysers on the rocky bottom that spew out particles and perhaps also microbes to the outside. Juice and NASA’s orbital probe Clipper, launching in 2024, may be able to locate the geysers and, in the event of the European mission, to identify possible pockets of liquid water that have remained close to the surface.

The last part of the project will come with a historical record: in 2034 Juice will become the first artificial satellite in orbit of a natural satellite: the moon Ganymede, bigger than Pluto and Mercury and the only one that has a magnetic field. The ESA probe will spend nine months in this world, with the goal of performing a tomography, as if it were a patient, which will include the most detailed map of its surface and an estimate of its interior structure.

Ganymede could hold more water than there is on the entire surface of the Earth. If so, it would also be located inside an ocean of salt water buried 93 miles (150 km) under the ice. It is possible that the moon’s enigmatic magnetic field is generated by the rotational movement of this enormous mass of liquid water. To find out, Juice has a magnetometer installed on the tip of a 10-meter antenna, manufactured by the Spanish company Sener, which will measure the magnetic field from a distance sufficient so that the rest of the ship’s systems do not cause interference.

In 2035 the probe will use its remaining propellant to head for the surface of Ganymede, where it will crash. The global agencies that monitor the contamination of other worlds with terrestrial life consider that there is no risk that if there are any microbes on board they might survive the conditions of this moon. For Juice, dying on Ganymede is also a way of making sure terrestrial life doesn’t invade the very interesting Europa.

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