Jupiter and the Juice launch: What you need to know

A scientific mission of great importance began at the spaceport in Kourou, French Guiana on Friday. The European Space Agency (ESA) is sending up its Jupiter Icy Moons Explorer, Juice, to ― well, explore three of Jupiter's icy moons.

Doesn't sound too exciting yet? Then consider that one of the mission's goals is to characterize "these moons as both planetary objects and possible habitats," according to ESA. In other words, the mission aims to find out if life could be possible on Ganymede, Europa or Callisto, or whether life has existed on the moons in the past.

The launch was originally scheduled for one day earlier, but had to be pushed because of lightning risk in Kourou on Thursday.

The Juice project is a mission of many firsts. The spacecraft, which is being sent up on an Ariane 5 rocket, will be the first to change orbits from another planet (Jupiter) to one of its moons. And it will be the first to orbit a moon other than the Earth's.

The total costs of the mission stand at around €1.6 billion ($1.7 billion). Juice will carry several high-tech systems on board, "including the most powerful remote sensing, geophysical and in situ payloads ever flown to the outer solar system," ESA says.

While the mission is  European-led, there has been wider international collaboration.NASA contributed one of the instruments, a UV imaging spectrograph. The Japanese space agency JAXA contributed hardware for several of the instruments on board the spacecraft, while the Israeli space agency ISA contributed hardware for a radio science experiment.   

If things go according to plan, Juice will arrive at Jupiter in July 2031 — a marathon journey time of eight years. It will do 35 flybys of the three moons between July 2031 and November 2034 and will then enter Ganymede's orbit, where it's scheduled to stay and collect information until December 2035.  

Here are a couple of facts to get you excited.

Jupiter, our solar system's largest planet

While the Juice mission is concerned with three moons, Jupiter has a total of 95 moons with confirmed orbits. 

It is the largest planet in our solar system, and twice the mass of all the other planets combined. As NASA puts it: "If Earth were the size of a nickel [a US five-cent coin], Jupiter would be about as big as a basketball."

Jupiter's size gives it a powerful magnetic field. Part of the Juice mission is to find out how this affects the icy moons surrounding the planet.

Scientists already know the magnetic field moves gases between Jupiter's moons. Sulphur and oxygen released by volcanos on Jupiter's volcanic moon Io reach three other moons Juice will be exploring. What researchers are looking to learn is how this process works.

The moons at the center of the Juice mission

Ganymede, Callisto, Europa and Io were discovered by Italian astronomer Galileo Galilei in 1610 and are known as the four "Galilean moons." They were the first objects found in our solar system to orbit a body other than the sun or Earth.

Ganymede, the Juice mission's primary target, is the only moon in our solar system that generates its own magnetic field. It's also the biggest moon in our solar system, with a diameter of 5,268 kilometers (3,273 miles) and a metallic core made up of an iron-heavy liquid. Its subterranean ocean is thought to hold more water than all of Earth's oceans combined. 

Callisto is Jupiter's second-largest moon and ESA scientists hope that by orbiting it, Juice will gather information about the environment around Jupiter in the planet's early days. Callisto is made up of equal parts rock and ice and may have a subsurface, liquid ocean located at depths greater than 100 kilometers.

Europa is slightly smaller than Earth's moon and possibly holds vast underground oceans. It is primarily made of silicate rock and has a water-ice crust. Juice scientists suspect that Europa may release water vapor into space via plumes and geysers. One the mission's main goals is finding out whether there are biosignatures and pockets of water on Europa ― signs of life.

The three moons are all named after figures from Greek mythology, according to which Ganymede was supposedly the most beautiful mortal on Earth and abducted by the gods to serve as the cup bearer of the king of the gods, Zeus. Callisto was a nymph who was turned into a bear and later became the constellation Ursa Major. Europa was the mother of King Minos of Crete and lover of Zeus, whose Roman equivalent is Jupiter.   

Jupiter's challenging environment

The Juice spacecraft will operate in extreme conditions. The area around Jupiter and its moons is one of the most intense radiation environments in our solar system. The temperature around the gas planet stands at a chilly -230 degrees Celsius (-382 degrees Fahrenheit). This contrasts starkly with the scorching 250 degrees Celsius that it will have to withstand during its Venus flyby on the way to Jupiter. 

The gravity-assisted flyby, a casual 300 million kilometer detour, will set the spacecraft on course for its 2031 arrival at Jupiter.

The researchers behind Juice hope that the mission will answer several questions on Jupiter's atmosphere, its magnetic field and how these factors interact with each other and influence the planet's moons.

The hope is that the answers to these questions will help scientists better understand the fundamental physics of planetary environments and eventually figure out whether life on one of Jupiter's moons would be possible.

Edited by: Fred Schwaller

Editor's note: This story was originally published on April 12, 2023, and updated after the rescheduled launch on April 14, 2023.