ESA’s Jupiter Icy Moons Explorer (Juice) is well on its way to exploring the cold satellites that may host extraterrestrial life. In a month, Juice will execute its first gravity assist in a double maneuver involving both the Moon and Earth. This groundbreaking “lunar-Earth gravity assist” will represent a milestone in space exploration. Never before has a spacecraft performed such a complex series of maneuvers.

Jupiter has a lot of moons — we’re not even sure how many. Some of them, like Europa or Ganymede, are particularly interesting. Although they’re frozen solid on the surface, researchers now believe that they harbor oceans of liquid water beneath. This makes these moons potential candidates for extraterrestrial life and definitely among the most interesting places in the solar system.

This is where Juice comes in.

The Jupiter Icy Moons Explorer mission was launched by the European Space Agency (ESA) on April 14, 2023. It’s an ambitious eight-year journey aimed at studying Jupiter and its three largest icy moons: Ganymede, Callisto, and Europa. The mission’s primary objective is to investigate these moons’ potential subsurface oceans.

When it gets to Jupiter, Juice will conduct detailed observations of Jupiter’s atmosphere, magnetosphere, and the surface and subsurface characteristics of its moons. The mission could provide unprecedented insights into the formation of planetary systems and the potential for extraterrestrial life.

But getting there is not so easy.

Gravitational slingshot

Our solar system is flat like a pancake. Flying from one place to the other requires a lot of fuel and energy. However, researchers have found a resource that greatly helps shuttles: gravity.

A gravity assist, also known as a gravitational slingshot, is a space navigation technique. This technique alters the path and speed of a spacecraft by utilizing the gravitational pull of a planet or other celestial body. By carefully flying close to the body, the spacecraft can “borrow” some of its orbital energy. The result is a significant change in the spacecraft’s velocity and trajectory without using additional fuel.

This maneuver is crucial for missions to distant planets, allowing spacecraft to achieve the necessary speed and direction while conserving onboard fuel.

In August 2024, the Earth will bend Juice’s trajectory through space, slowing it down and redirecting it on a course for Venus, where a similar maneuver will happen. The innovation here is that Juice will also leverage the Moon’s gravitational pull to fine-tune its trajectory before encountering Earth’s more substantial gravity. This technique not only conserves fuel but also shortens the mission timeline, making it a critical component of Juice’s flight plan.

So this “exotic” route, while longer than a direct flight to Jupiter, is both faster and more efficient. It’s basically a shortcut to Jupiter.

Direct travel to the gas giant, located approximately 800 million kilometers from Earth, would require an impractical amount of onboard fuel—around 60 tons. Additionally, Juice would need even more fuel to decelerate upon reaching Jupiter to avoid overshooting into deep space.

As you may imagine, this is anything but easy. Executing the Earth-moon maneuver requires Juice to navigate with pinpoint accuracy. The spacecraft must arrive at the Moon and then at Earth at the precise moment, speed, and direction needed to optimize its trajectory. This navigation challenge is like threading a needle at high speed while maintaining an almost impossibly tight margin for error.

For now, however, things are looking to be on track.

Juicy science incoming

Juice’s journey to Jupiter is the culmination of two decades of meticulous planning by ESA’s mission analysis team. This intricate dance of gravity assists is a pinnacle of spacecraft navigation and energy conservation. Scientists carefully plot each maneuver to ensure that Juice not only reaches Jupiter but does so with the necessary speed and direction to enter orbit and begin its scientific mission.

The spacecraft is expected to reach the Jupiter system in 2031; from thereon, it’s expected to send a trove of scientific data.

It features an advanced camera system that can capture high-resolution images, providing detailed geological context and helping correlate spectral, laser, and radar data. It’s also equipped with a spectrometer that will observe cloud features and minor gas species on Jupiter while analyzing the composition of ices and minerals on the moons’ surfaces.

The Ganymede Laser Altimeter (GALA) will map the topography and study tidal deformations on Ganymede, offering insights into its internal structure, while the Radar for Icy Moons Exploration (RIME) will explore subsurface structures down to 9 km deep — potentially getting data about the moon’s liquid oceans. Add in magnetic and gravity sensors that can conduct precise field measurements, and you have a near-complete suite of instruments to study the moons’ geology and understand them better than ever before.