It’s been a busy week or so for news stories about the solar system! Last Friday was the list time we would get to see Juice, Jupiter Icy Moons Explorer, before it was shipped off to Kourou in French Guiana for launch on an Ariane 5 rocket in April. Juice is heading off to the Jupiter system to explore the planet, its magnetic fields, and some of its largest moons: Europa, Ganymede and Callisto. This mission has been in development for years, having been selected in 2012 as the first “large-class” mission in ESA’s Cosmic Vision 2015-2025 programme, and has contributions from both NASA and the Israeli Space Agency.
Jupiter Icy Moons Explorer
As BBC local radio stations amusingly described it last Friday, Space Juice will achieve several firsts. It will be the first spacecraft to orbit a moon in the outer solar system – we’ve orbited our own Moon, but never the moon of another world. It will also be the first flyby of the Earth-Moon system (called a lunar-earth gravity assist), which is a flyby of the Moon first and then another flyby of the Earth just 1.5 days later – by doing this manoeuvre, Juice will save a significant amount of propellant.
Flybys are always important for getting to the outer solar system, they can save you a lot of propellant which gives you more mass to use for funky, exciting science instruments! In this case, although Jupiter is only about 600 million km from Earth, there is no rocket powerful enough to go directly there. By making flybys of Earth (August 2024), Venus (August 2025), and Earth again (September 2026, January 2029), Juice will travel more like 6.6 billion kilometres! It’s worth it though, for the extra science payload.
What’s it going to do? Juice will give us the most detailed view of Jupiter and its icy/water world moons (Ganymede, Callisto and Europa). Jupiter is the archetype gas giant planet. We keep finding Jupiter-like planets around other stars, but they are very difficult to study due to their distance – it’s very hard to image them. Jupiter is much easier to study, and learning more about this solar system giant can help us understand those Jupiter-like exoplanets in more detail. All three moons thought to have subsurface oceans of liquid water, so are important places to go searching for evidence of life.
Jupiter and its moons are like a mini solar system. Jupiter sits in the middle of a dancing melee of smaller rocky objects in (almost) circular orbits around it. Why will Juice visit these three moons in particular? Well, we think they all have some liquid water below the surface. And they are all quite different, so comparing them will be really interesting.
Europa has an obvious icy crust, so the surface features are actively changing. Imagine watching the ice creak and move slowly in Antarctica – but on a planetary scale! Juice will make a couple of flybys of Europa to search for biosignatures, to see how much water there might be under the surface, and explore the moon’s geology and activity. Europa is very close to Jupiter, it’s a very harsh environment so Juice will only make two flybys of this moon.
Ganymede is older and has a less active crust. It has an older surface which is rocky, rather than icy, and gives us a window on a geological record that spans billions of years of solar system history. It’s also the only known moon with a magnetic field, implying that it has a molten core like the Earth. Juice will explore Ganymede’s magnetic field, look for subsurface pockets of water or evidence of a sub-surface ocean, measure its complex core, its interaction with Jupiter, and help us determine the potential for habitability – now, or in the past.
Callisto has the oldest known surface in the solar system. It appears heavily cratered, an indicator of its age, and is inactive (no volcanos on Callisto!). Given its age it will help us explore the history of our own solar system. It may also contain a salty subsurface ocean, something else the sensors on board Juice will be looking for.
After launch (hopefully!) in April, Juice will then set off on its eight-year cruise out to Jupiter. On the way it will have to brave harsh radiation and temperature environments (+250C at Venus flyby, -230C at Jupiter!), but it has been designed to cope with all this. For its science operation phase it will be a long way from Earth, so it will need a powerful antenna to send back data, and largely autonomous systems due to the time delay. Sunlight is 25 times weaker at Jupiter than on Earth, so it also has very large solar panel arrays (an area of 85 square metres!) producing 700-900 Watts (plus batteries for use during eclipses).
Jupiter will be a busy place over the next decade or so. Juno is already in orbit, mapping Jupiter’s gravity and magnetic fields, and NASA are also sending Europa Clipper which will arrive in 2030and will work in collaboration with ESA’s Juice. Keep an eye out for results from these missions!
For much more on Juice, its instruments and mission goals, see ESA’s Juice Launch Kit.