The European Space Agency's Jupiter probe, Juice, will fly by Earth and the Moon on 19 - 20 August 2024, and may even be a visible object in the night sky.
In what's being described by ESA as a "double world first", the Jupiter Icy Moons Explorer (Juice) will perform the first ever lunar flyby and the first ever double gravity assist manoeuvre.
The flyby is being undertaken as part of Juice's journey to Jupiter, and will use Earth's gravity to change the spacecraft's speed and direction as it makes its way to the gas giant.
This is known as a 'gravity assist'.
Juice Earth flyby explained
ESA's Juice mission is tasked with studying Jupiter, the largest planet in the Solar System, and its icy Galilean moons Europa, Ganymede and Callisto.
The Juice mission launched from Earth on 14 April 2023, beginning its journey to Jupiter. So what's it doing returning to Earth? Shouldn't it be well on its way?
Getting a spacecraft to travel from Earth to another body in the Solar System isn't as simple as drawing a straight line between the two and following that trajectory.
Jupiter is 800 million km away from Earth, and so a spacecraft like Juice needs to be launched on powerful rocket in order to escape our planet's gravity and begin its journey across the Solar System.
And if it were to simply head straight for Jupiter, an enormous amount of fuel would be required to effectively 'brake' once at the Jovian system, so Juice could enter a stable orbit around the planet and not simply fly past it.
This braking can be done earlier on in the journey by using the gravity of the other planets to alter the spacecraft's course, enabling it to change direction and slow down.
Sometimes a planet's gravity can even be used to speed up a spacecraft, whereby a probe is allowed to hurtle towards the body in question before slingshotting away at the last minute.
What will happen during the flyby?
As Juice flies by Earth, our planet's gravity will alter Juice’s trajectory through space, slowing it down and redirecting it on course for another flyby: that of Venus in August 2025.
Juice will speed up as it flies by Venus and then twice by Earth.
So why not just use this 2024 Earth-Moon flyby to speed Juice up?
"Somewhat counterintuitively," says ESA, "using the lunar-Earth flyby to slow Juice down at this point in its journey is actually more efficient than using the flyby to speed it up.
"If we had instead used this flyby to give Juice a boost towards Mars, we would have had to wait a long time for the next planetary flyby.
"This first ‘braking’ manoeuvre is a way of taking a shortcut through the inner Solar System."
"It’s like passing through a very narrow corridor, very, very quickly," says Juice Spacecraft Operations Manager Ignacio Tanco, "pushing the accelerator to the maximum when the margin at the side of the road is just millimetres."
From 17–22 August, Juice will be in contact with ground stations around the world, as engineers keep an eye on the data and make required adjustments.
Bonus science
Juice's instruments will be turned on as the spacecraft passes by the Moon and Earth.
This will enable the team to test the instruments' ability to collect data from Solar System body in space for the first time.
This gives the science team a good chance to calibrate and tweak the instruments before Juice arrives at Jupiter.
Will Juice be visible from Earth?
According to ESA, the Juice spacecraft could be visible from Earth during the flyby, but you'll need to have clear skies and, crucially, be in the right location.
Juice's close approach to Earth will be 23:57 CEST on 20 August (01:57 UTC on 21 August) 2024.
Juice will fly over Southeast Asia and the Pacific Ocean, meaning anyone in that part of the world may be able to see it in the night sky.
Powerful binoculars or a telescope will be needed if you want to catch a glimpse of the Juice spacecraft.
But perhaps more exciting will be Juice's view of us, rather than the other way round.
The spacecraft has two onboard monitoring cameras and will be capturing images throughout the Moon-Earth flyby.
Expect to see them shared widely on this very website and our social media channels.
If you do manage to catch a glimpse (or even an image?) of Juice during the flyby, share it with us via contactus@skyatnightmagazine.com.
