Figure 0-1. The flyby between 25 September and 1 October 2026, reconstructed from JPL Horizons ephemerides and from the mission's SPICE files: the spacecraft's position, its orientation and what each instrument had in its field of view. The animation starts by itself, and the timeline at the bottom runs more slowly near perigee; click an event in the list to jump to it. The “Director” view follows a camera path prepared in advance. With a mouse, drag to rotate and hold Ctrl to zoom with the wheel; on a phone, a finger dragged sideways rotates the scene, and the “Full screen” button gives full control. Earth and the Moon are to scale; the spacecraft is greatly enlarged.
On 28 September 2026, at 11:45 UTC (14:45 in Romania), the European probe JUICE passed 8,642 km above the Indian Ocean. It did not fire its main engine: it let Earth's gravity bend its path by 21° and add 3.5 km/s to the speed at which it circles the Sun.
It was the third of the four gravity assists taking it to Jupiter, where it arrives in July 2031.
- Perigee
- 28 Sept 2026, 11:45:11 UTC
- Where
- above the Indian Ocean, at 22.3° S, 82.7° E
- Altitude
- 8,642 km
- Speed
- 13.12 km/s relative to Earth
- Deflection
- 21.0°
- Gain
- +3.50 km/s around the Sun
- Eclipse
- 2 h 53 min in Earth's full shadow, ending ten hours before perigee
1.0Eight years to Jupiter
JUICE (Jupiter Icy Moons Explorer) left Kourou on 14 April 2023, on the second-to-last Ariane 5. No rocket could send it straight to Jupiter: it would have had to leave Earth much faster, and on arrival it would have needed even more fuel to brake and enter orbit. The route chosen takes eight years and passes four times close to other bodies, which change the spacecraft's orbit with almost no fuel.
Each flyby has a different job. The double Moon–Earth flyby of August 2024, the first of its kind ever, was a braking manoeuvre: it shrank the orbit so that the spacecraft could reach Venus. Venus enlarged it again in August 2025. The September 2026 flyby and the one in January 2029 stretch it, step by step, out to Jupiter's distance.
Date (UTC) Body Altitude Speed change Orbit after flyby
vs the Sun perihelion–aphelion
─────────────────────────────────────────────────────────────────────────────────
14 Apr 2023 launch
19 Aug 2024, 21:15 Moon 752 km
20 Aug 2024, 21:56 Earth 6,836 km −3.02 km/s¹ 0.64–1.01 AU
31 Aug 2025, 05:29 Venus 5,088 km +3.78 km/s 0.71–1.58 AU
28 Sept 2026, 11:45 Earth 8,642 km +3.50 km/s 0.85–2.41 AU
Jan 2029² Earth ≈ 4,600 km +3.45 km/s 0.94–5.25 AU
Jul 2031² Jupiter orbit insertion
Date Body Altitude speed change vs the Sun · orbit after ─────────────────────────────────────────── 14 Apr 2023 launch 19 Aug 2024 Moon 752 km 20 Aug 2024 Earth 6,836 km −3.02 km/s¹ · orbit 0.64–1.01 AU 31 Aug 2025 Venus 5,088 km +3.78 km/s · orbit 0.71–1.58 AU 28 Sept 2026 Earth 8,642 km +3.50 km/s · orbit 0.85–2.41 AU Jan 2029² Earth ≈ 4,600 km +3.45 km/s · orbit 0.94–5.25 AU Jul 2031² Jupiter orbit insertion
The altitudes, speed changes and orbits are calculated here from the trajectory, not taken from press releases. The speed relative to the Sun is compared at the flyby distance, before and after. ¹ For the double Moon–Earth flyby, taken as a whole. ² From the planned trajectory; the dates and values may change.
2.0How you gain speed by passing a planet
Seen from Earth, the flyby is symmetrical. JUICE comes in from space with a certain speed relative to the planet, called the speed at infinity, v∞, speeds up as it falls towards perigee and leaves with exactly the same speed. This time, v∞ was 10.91 km/s, and at perigee the spacecraft reached 13.12 km/s. In Earth's frame of reference, the flyby gives it no energy; it only changes its direction.
The gain appears when you look from the Sun. The spacecraft's velocity relative to the Sun is the sum of Earth's orbital velocity, 29.7 km/s, and the spacecraft's velocity relative to Earth. The flyby rotates the second arrow without changing its length, and Earth's arrow stays the same. If the rotation brings v∞ closer to the direction in which Earth is moving, the sum grows. For JUICE it grew from 31.53 to 35.03 km/s.
The energy does not come from nowhere. Earth receives an equal and opposite push, but with its mass, its speed changes by something of the order of 10−18 m/s.
- Altitude
- Deflection
- Speed relative to the Sun
- Gain
- Orbit after the flyby
- Orbital period
Passing lower, JUICE would have been deflected more and would have gained more: at 500 km, almost 6 km/s, and the orbit would have reached 3.8 AU from the Sun. But the aim is not the highest speed; it is the right orbit, the one that brings the spacecraft back to Earth in January 2029, exactly where it needs to be for the last flyby. The side you pass on matters too: JUICE passed through Earth's wake, that is, behind it relative to the direction in which it moves along its orbit. On the opposite side, at the same altitude, the flyby would have slowed the spacecraft down by 3.9 km/s, as the double flyby of 2024 did on purpose.
3.0The night before perigee
JUICE approached Earth from the side opposite the Sun, so it crossed the planet's shadow cone in the night before perigee, hundreds of thousands of kilometres away. It entered the umbra beyond the Moon's orbit and stayed there for almost three hours, between 22:50 and 01:43 UTC, with Earth's disc covering the Sun completely.
Date and time (UTC) What happens Distance ───────────────────────────────────────────────────────────────────── 27 Sept, 19:29:38 enters penumbra 650,062 km 27 Sept, 22:50:07 enters umbra 518,087 km 28 Sept, 01:42:46 leaves umbra 404,286 km 28 Sept, 02:33:23 passes 124,638 km from the Moon 370,890 km 28 Sept, 04:09:23 leaves penumbra 307,482 km 28 Sept, 11:15–11:30 passes over Australia 28 Sept, 11:45:11 perigee, at 8,642 km altitude 15,017 km
Date and time (UTC) Distance what happens ───────────────────────────────── 27 Sept, 19:29:38 650,062 km enters penumbra 27 Sept, 22:50:07 518,087 km enters umbra 28 Sept, 01:42:46 404,286 km leaves umbra 28 Sept, 02:33:23 370,890 km passes 124,638 km from the Moon 28 Sept, 04:09:23 307,482 km leaves penumbra 28 Sept, 11:15–11:30 passes over Australia 28 Sept, 11:45:11 15,017 km perigee, at 8,642 km altitude
Distances are measured from Earth's centre. ESA announced the shadow interval as 19:24–04:03 UTC; the model here treats Earth as a sphere without an atmosphere, and the difference, a few minutes, does not change the sequence of events.
Without light, the solar panels produce no power, so the spacecraft ran on batteries for almost nine hours. The team decided in advance which observations would be made during this interval, so that the batteries would not run down completely. In the animation, the timeline at the bottom colours the penumbra light violet and the umbra dark violet, and the indicator next to “Telemetry” changes from “Sunlit” to “Penumbra” and “Umbra”.
The magnetotail also stretches out on the night side: Earth's magnetic field, drawn out by the solar wind like a windsock. JUICE flew through it for several days and measured the magnetic field and the charged particles there, while the European–Chinese mission Smile watched the aurorae and the environment close to Earth. Together, the two can link what happens far out in the tail with what is seen at the poles.
4.0What the instruments looked at
Between 23 September and 3 October, the ten science instruments were switched on, one after another, to observe Earth and the Moon. For the teams it was a rehearsal: instruments behave differently in space than in the laboratory, and at Jupiter each of the 35 flybys of the moons will be a unique opportunity. It was the third rehearsal of this kind, after the double flyby of 2024 and the 2025 observations of the interstellar comet 3I/ATLAS.
The “Instruments” panel in the animation shows, moment by moment, which celestial body each instrument had in its field of view, computed from the spacecraft's orientation and the geometry of the instruments: the JANUS science camera, the navigation camera, the MAJIS spectrometer, the UVS ultraviolet spectrograph, the GALA laser altimeter, a monitoring camera, and the high-gain and medium-gain antennas. The fields of view of JANUS and of the navigation camera are also drawn in the scene. The panel shows where the instruments were pointed, not whether they were switched on.
The navigation camera, which at Jupiter will guide the spacecraft past the moons, looked at the edge of the Moon to test a new optical navigation technique. The two monitoring cameras, mounted to watch the antennas and booms unfold after launch, photographed Earth: the images taken shortly after perigee show Africa and Madagascar. The high-resolution images from JANUS will be published once the data have reached Earth and have been checked by the teams.
5.0What comes next
The last Earth flyby is scheduled for January 2029. On the planned trajectory, JUICE will pass at about 4,600 km, and the aphelion of its orbit will rise to 5.25 AU, Jupiter's distance from the Sun. The spacecraft reaches Jupiter in July 2031 and enters orbit around the planet. Then come 35 flybys of Ganymede, Callisto and Europa, and in 2034 it settles into orbit around Ganymede: it will be the first spacecraft to orbit the moon of another planet.
The fuel saved now will count then. In the four weeks before the flyby, only one trajectory correction was needed, out of six windows prepared, and ESA says the flyby used only a small part of the reserve set aside for it. The rest is kept for the manoeuvres at Jupiter.
6.0How the flyby was reconstructed
The trajectory comes from JPL Horizons, where JUICE has the code −28: more than 5,000 states, denser near perigee, interpolated in the browser with cubic Hermite polynomials. The spacecraft's orientation, its shape and the instruments' fields of view come from the SPICE files published by ESA (the juice_plan_v473_20260917_002 set), that is, from the operations plan. Earth's rotation is computed from the Earth rotation angle and the IAU 2006 precession; the ground track was compared with the sub-spacecraft point given by Horizons, and the largest difference is under a kilometre.
The minimum distance, 15,016.8 km from Earth's centre, differs by 0.3 km from the one in ESA's SPICE files. The altitude of 8,642 km is measured from the Earth ellipsoid; ESA announced 8,640 km, about 20° and about 3.5 km/s. The deflection and the speed change in the animation and in figure 2.0-1 are calculated here, from the trajectory. The images of Earth come from NASA Blue Marble Next Generation and Black Marble 2016, and the map of the Moon from the NASA SVS CGI Moon Kit, made with LRO data.
7.0A few terms
- Gravity assist (flyby)
- Passing close to a planet or a moon to change the spacecraft's speed and direction without using fuel.
- Speed at infinity, v∞
- The spacecraft's speed relative to the planet, far from it. It is the same on the way in and on the way out; the flyby only changes its direction.
- Perigee
- The point of the trajectory closest to Earth. For other bodies, the general term is periapsis.
- Perihelion and aphelion
- The points of an orbit around the Sun closest to it and farthest from it.
- Astronomical unit (AU)
- The average distance between Earth and the Sun, about 149.6 million kilometres. Jupiter is about 5.2 AU from the Sun.
- Umbra and penumbra
- In the umbra, Earth covers the Sun's disc completely; in the penumbra, only part of it.
- Magnetotail
- The part of Earth's magnetic field stretched out by the solar wind on the night side, to hundreds of thousands of kilometres.
- Patched conics
- The approximation in which, close to a planet, the spacecraft feels only the planet's gravity, and far from it only the Sun's. The path is split into pieces of ellipses and hyperbolas.
- Ephemerides and SPICE
- Ephemerides are tables of a body's position and velocity over time. SPICE is NASA's file system through which missions publish the trajectory, the spacecraft's orientation and the geometry of the instruments.
8.0Sources
- ESA, Juice to fly past Earth for third gravity assist, 21 September 2026: the announced altitude, deflection and gain, the shadow, the pass over Australia, the trajectory corrections.
- ESA, Successful Earth flyby improves Juice’s course to Jupiter, 28 September 2026: the result of the flyby, the instruments, the magnetotail and Smile.
- ESA, Juice images Earth during Earth flyby, 28 September 2026, and Juice’s September 2026 Earth flyby: the movie, 1 October 2026: the monitoring camera images.
- ESA, Juice rerouted to Venus in world’s first lunar-Earth flyby, 21 August 2024.
- ESA, Juice: why’s it taking sooo long, 19 September 2023: why the journey takes eight years.
- NASA/JPL, Horizons: the ephemerides of JUICE (−28), Earth, the Moon, the Sun and the planets.
- ESA, SPICE for JUICE: the spacecraft's orientation, its shape and the instruments' fields of view.
Educational explainer. The trajectory, the spacecraft's orientation and the fields of view come from the mission's ephemerides and SPICE files; the values for 2029 and 2031 come from the planned trajectory and may change. Figure 2.0-1 is a simplified calculation, with patched conics. Page generated on 7 October 2026 at 07:02 UTC. Also in Romanian: JUICE trece pe lângă Pământ.