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Juice uses Earth's gravity to save fuel on its Jupiter journey

English हिंदी ಕನ್ನಡ മലയാളം தமிழ் తెలుగు

First brief 29 Sep, 2:17 pm IST Updated 29 Sep, 2:17 pm IST 1 development 3 min read Latest ↓

Earth from Juice, 28 Sep 2026 — ESA/Juice/JMC; S. Schmauß · CC BY-SA 3.0 IGO

Where it stands

Europe's Juice spacecraft flew past Earth on 28 September 2026 and used the planet's gravity to change its route. The spacecraft is travelling to Jupiter to study the giant planet and three of its icy moons. Coming back near Earth is part of that journey, not a return from Jupiter. At its closest point, Juice passed 8,640 km above the Indian Ocean. Careful navigation meant the team used only a small part of the fuel set aside for this encounter. The saved fuel remains available for later work around Jupiter and its moons. The flyby also let scientists test instruments by observing the more familiar Earth and Moon. Juice still has a long journey ahead. Another Earth flyby is planned for January 2029, followed by arrival at Jupiter in 2031. This week's success completes one important step. The mission's observations at Jupiter, including its search for conditions that could support life, are still to come.

Background

A rocket can launch a spacecraft away from Earth, but reaching another planet needs more than pointing at it. Earth and the destination are both moving around the Sun. The spacecraft must follow a path that meets the destination at the right time and with a manageable speed. Changing that path with engines alone can consume a great deal of fuel. A gravity assist offers another way. As a spacecraft passes a moving planet, the planet's gravity bends its path. With the right approach, the spacecraft gains energy from the planet's motion around the Sun. The planet gives up an extremely small amount of energy, while the much lighter spacecraft receives a useful boost. Energy is transferred, not created. Mission planners arrange these encounters before launch and make small corrections along the way. The route may look like a detour, but it can achieve a journey that would otherwise need much more fuel. Saving fuel during the cruise matters because the spacecraft must also change course and position once it reaches its scientific destination. For Juice, that destination includes Ganymede, Europa and Callisto, three large moons of Jupiter. Scientists have evidence suggesting oceans beneath their icy surfaces. Studying the ice, interiors and surroundings can help explain whether these worlds have conditions suitable for life. Finding suitable conditions would be different from discovering living organisms.

How it developed

April 2023; Juice begins its journey

How it started
An eight-year route is designed around planetary encounters

Juice launched in April 2023 on an ESA-led mission, with contributions from international partners including NASA. The mission is designed to study Jupiter and its large icy moons. It will first travel around Jupiter and make close passes of the moons, before entering orbit around Ganymede. The long cruise uses planetary encounters to shape the route. These passes reduce the amount of engine work needed for the journey. The spacecraft still carries fuel for course corrections and later operations; gravity assists do not remove that need.

NASA European Space Agency European Space Agency
28 September 2026; Earth flyby completed

New fact
Precise navigation leaves more fuel for later observations

Juice made its closest approach at 5:15 pm Indian time. The flyby changed its direction by 20 degrees. In the preceding weeks, controllers needed only one small course correction out of six opportunities reserved for that purpose. ESA says the resulting fuel saving leaves more available for observations at Jupiter. The encounter also gave instrument teams a chance to check measurements against Earth and the Moon. Such checks help scientists understand how an instrument behaves before relying on it at a distant, less familiar world. Further images and measurements will be assessed after they reach Earth.

European Space Agency NASA

Why it matters for UPSC

GS3 · Space missionsGS3 · Gravity assists

For GS3, connect gravity assists with conservation of energy and fuel limits in space travel. Explain why a spacecraft may revisit Earth while travelling to an outer planet. Distinguish a completed navigation step from a future scientific finding about an icy moon.

Key terms

JuiceThe European Space Agency's Jupiter Icy Moons Explorer. It is a robotic spacecraft studying Jupiter and its icy moons, not a crewed mission. Its targets include Ganymede, Europa and Callisto, with a later orbit around Ganymede planned for closer study.

Gravity assistA close pass that uses a planet's gravity and motion to change a spacecraft's path and energy. The approach determines whether the spacecraft gains or loses energy relative to the Sun. The method can save fuel that engines would otherwise need for a similar change.

FlybyA passage near a planet, moon or other object without entering orbit around it. A flyby can support navigation, scientific observations, or both. Juice's Earth flyby was a brief encounter along its wider journey, not a landing or a permanent Earth orbit.

TrajectoryThe path followed by a moving object through space. Gravity, speed and engine firings all affect a spacecraft's trajectory. A small adjustment made early can change where it passes a planet much later, which is why precise navigation matters.

PropellantMaterial carried by a spacecraft and expelled to produce thrust. Thrust changes its motion. A spacecraft has a limited supply, so spending less on one manoeuvre can leave more for later operations. Gravity assists help conserve this supply but do not replace every engine firing.

Instrument calibrationChecking an instrument's readings against a known or well-understood reference. This helps identify offsets and other effects that could distort measurements. Observing familiar objects during the cruise gives scientists a chance to test equipment before interpreting unfamiliar conditions near Jupiter.

HabitabilityWhether a place has conditions that could support life, such as suitable chemistry and access to liquid water and energy. It is a question about the environment. Evidence that a moon may be habitable is not evidence that organisms have actually been found there.

Sources (4)

NASA · official · Juice: mission, targets and July 2031 arrival
European Space Agency · official · Juice factsheet
European Space Agency · official · What are gravity assists?
European Space Agency · official · Successful Earth flyby improves Juice's course to Jupiter