BepiColombo launch — to Mercury

Europe and Japan's Mercury mission — seven years of braking through nine flybys to fall sunward.

The moment of BepiColombo launch — to Mercury: https://nowsky.org/e/bepicolombo-launch — opens at the right place and time, replayable, no login.

Available views: Orbit ✓ · Sky — (not visible in the sky)

The story

On 20 October 2018 BepiColombo, a joint mission of ESA and JAXA, left for Mercury on an Ariane 5. Europe's Mercury Planetary Orbiter (MPO) and Japan's Mercury Magnetospheric Orbiter (Mio) ride together on an electric-propulsion module as a single stack. The name honours Giuseppe "Bepi" Colombo, the Italian mathematician who designed Mariner 10's Mercury trajectory in the 1970s.

Going to Mercury is a descent. The acceleration gained by falling toward the Sun has to be cancelled by nine gravity assists over seven years — one at Earth, two at Venus, six at Mercury — before orbit insertion is possible; that is why it is harder than going to Jupiter. Earth was passed in April 2020, Venus in 2020–2021 and Mercury six times from 2021.

A power problem in the propulsion module in April 2024 reduced thrust and delayed arrival by eleven months; orbit insertion is scheduled for 27 November 2026. The two orbiters then separate — MPO to survey the surface and interior from low orbit, Mio to study the magnetosphere from a long ellipse — measuring the same planet inside and out at once.

It is the first Mercury orbiter since MESSENGER (2011–2015) and the first time two agencies operate two orbiters at one planet simultaneously. The orbit replay shows the spiral descent winding in around the Sun.

Why it matters

Mercury is the nearest planet and the least explored — only Mariner 10 (1974) and MESSENGER have visited, and the southern terrain and the interior are still roughly mapped. BepiColombo aims to map the whole surface and to explain the enormous core, 85 percent of the planet's radius.

Two orbiters measuring at once from different orbits is the point. When the solar wind strikes Mercury's magnetosphere, simultaneous readings near the surface (MPO) and far out (Mio) cannot be obtained by one spacecraft — the same reason multi-satellite missions became standard for Earth's magnetosphere.

Mercury was the first test bed of general relativity (the precession of its perihelion). BepiColombo's precise ranging doubles as an experiment measuring relativistic parameters in the Sun's gravitational field an order of magnitude better than before.

How to watch

BepiColombo is near Mercury and cannot be seen from the ground. Select it in the orbit view for its current position and its track over the last 120 days, winding in resonance with Mercury's orbit; move the time to 27 November 2026 for the arrangement at the planned orbit insertion.

The orbit replay runs from the 2018 launch through nine flybys of Earth, Venus and Mercury to orbit insertion; at high speed the orbit can be seen tightening sunward at each pass.

Mercury never strays more than 28° from the Sun and appears only low in the dawn or dusk sky. Select Mercury in the sky view for when it is visible from your location, its bearing and its phase.

See this for yourself — replay the moment in the orbit view

Background

During the six Mercury flybys MPO's monitoring cameras photographed the surface at close range, and on the fourth pass in September 2024 imaged the permanently shadowed craters of the south pole from a new angle for the first time. Most science instruments cannot be used before orbit insertion because of the stacked configuration.

MPO's science mission is one year after insertion, extendable to two. Surface temperatures of 430 °C mean the orbiters' thermal design sets the limit of the mission; Mio spins to keep changing the face it turns to the Sun.

The propulsion module is jettisoned just before insertion and left in solar orbit; the two orbiters then settle into their own orbits on chemical thrusters.

BepiColombo’s transfer module carries the four largest ion engines ever flown on a European spacecraft, firing two at a time for up to 290 millinewtons of thrust — the weight of a few coins, but run for thousands of hours it handles the orbit adjustments between flybys. When a power problem in April 2024 cut thrust to 90 percent of design, ESA chose an alternative trajectory reordering the remaining flybys and delaying arrival by eleven months, which preserved the science mission intact.

FAQ

Why does it take seven years?

The speed gained by falling sunward has to be shed with nine gravity assists before orbit insertion is possible.

When does it arrive?

Orbit insertion is scheduled for 27 November 2026, eleven months late after a 2024 propulsion problem.

Are there two spacecraft?

Yes — Europe's MPO (surface and interior) and Japan's Mio (magnetosphere) fly as one stack and separate on arrival.

Who is it named after?

Giuseppe "Bepi" Colombo, the Italian mathematician who designed Mariner 10's Mercury trajectory.

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Times and figures are approximate — verify with official sources when planning travel. Simulation uses J2000 mean elements.