The European Space Agency’s Juice spacecraft has successfully completed the first ever Moon-Earth flyby on its way to Jupiter.
The Jupiter Icy Moons Explorer made its close approach to the Moon at 21:15 UTC on 19 August, before making a close approach whizzing past Earth at 21:56 UTC on 20 August.
Juice’s 2024 Earth-Moon flyby was a key moment for the mission.
Juice flew 6,840km above Southeast Asia and the Pacific Ocean, capturing images of Earth and our Moon with its onboard cameras, recording data with its scientific instruments.
The move was part of a gravity-assist manoeuvre to reroute the Juice spacecraft’s journey through space on its way to Jupiter.
This is a common technique used to navigate planetary probes across the Solar System to reach their destination.
Flying directly from Earth to another planet in the Solar System, then effectively ‘braking’ to enter orbit around that planet, would consume too much fuel.
Instead, flybys of other Solar System bodies are used to speed up, slow down or reroute a space probe.
The flyby of the Moon sped up Juice by 0.9 km/s relative to the Sun, guiding it towards Earth.
Then the flyby of Earth slowed down Juice by 4.8 km/s relative to the Sun, guiding it onto a new trajectory towards Venus
ESA says the manoeuvre was risky, but it saved the mission around 100–150 kg of fuel.
“The gravity assist flyby was flawless, everything went without a hitch, and we were thrilled to see Juice coming back so close to Earth,” says Ignacio Tanco, Spacecraft Operations Manager for the mission.
“Thanks to very precise navigation by ESA’s Flight Dynamics team, we managed to use only a tiny fraction of the propellant reserved for this flyby.
“This will add to the margins we keep for a rainy day, or to extend the science mission once we get to Jupiter.”
Juice data on Earth and the Moon
Planetary scientists can’t have a spacecraft fly by so close to Earth and the Moon without taking the opportunity to do some science!
So while the main aim of the flyby was to alter Juice’s trajectory, the team took the opportunity to test out Juice’s science instruments.
All ten of Juice’s instruments were switched on during the Moon flyby; 8 of those were switched on for the Earth flyby.
ESA says more images and spectra on Earth and the Moon will be published over the next few weeks.
“The timing and location of this double flyby allows us to thoroughly study the behaviour of Juice’s instruments,” says Claire Vallat, Juice Operations Scientist.
“It happens early enough in Juice’s journey that we can use the data to prepare the instruments for arrival at Jupiter.
“And given how well we know the physical properties of Earth, the Moon, and the surrounding space environment, it’s also the ideal location to understand how the instruments respond to a real target.”
And now for Venus
Juice’s next step will be a meeting with Venus in August 2025.
This will redirect the spacecraft towards Earth, where it will fly by our planet in September 2026 and again in January 2029: two more boosts before it arrives in orbit around Jupiter in July 2031.
There it will begin its main mission, studying Jupiter and three of its large Galilean moons, Ganymede, Callisto and Europa.
These moons are targeted because they are thought to harbour subsurface oceans of liquid water.
Water being a primary condition for life as we know it, this makes them potentially habitable worlds and a key target for planetary scientists exploring the possibility that life might exist – or might ever have existed – beyond Earth.