BepiColombo Completes First Mercury Flyby

The joint Japanese/European Space Agency’s Mercury mission encountered the innermost planet for the first time this past weekend.

Mercury (annotated) as seen from BepiColombo during Friday’s flyby. ESA

Welcome to Mercury. An ambitious mission completed its first flyby of its final destination this past Friday, as the joint JAXA/ESA BepiColombo made its first flyby of the innermost world.

The flyby occurred on Friday, October 1^st at 23:34 UT/7:34 PM EDT, as the spacecraft skimmed just 199 kilometers above Mercury’s surface. Images relayed back depicted a crater-marked surface, very similar to Earth’s Moon.

The name ‘BepiColombo’ comes from the 20th century Italian scientist and mathematician Giuseppe ‘Bepi’ Colombo, who first pioneered the flyby gravitational assists now used by planetary missions today. The spacecraft was launched atop an Ariane 5 rocket out of Guyana Space Center on October 20, 2018, and is really composed of two spacecraft: the European Space Agency’s Mercury Planetary Orbiter and JAXA’s Mercury Magnetospheric Orbiter (MPO and MMO respectively), stacked one on top of the other.

The cameras on the Mercury Transfer Module were positioned looking back at Mercury, past the spacecraft instrument boom in the foreground.

Unfortunately, BepiColombo made its closest approach over the nighttime side of the planet, but managed to snap images along the sunrise day/night terminator a few minutes after its closest pass until about four hours out.

Entering the orbit of a planet in the inner solar system is difficult, and BepiColombo must make nine planetary flybys in total to reach orbit around Mercury on December 5, 2025: One of Earth, (completed in April 2020), two of Venus (also complete), and six of Mercury. Next up, BepiColombo will fly past Mercury a second time on June 23, 2022.

“The flyby was flawless from the spacecraft point of view, and it’s incredible to finally see our target planet,” Says Elsa Montagnon (ESA-Spacecraft Operations Manager) in a recent press release.

Though Mercury superficially resembles our Moon, it is much denser, and has no analog to the bright surface highlands seen on the lunar surface: instead, Mercury is almost uniformly dark.

Mercury has always been difficult to explore with Earth-based telescopes, owing to its close proximity to the Sun. NASA’s Mariner 10 gave us the first good look at Mercury during its March 29, 1974 flyby, managing to map about 45% of Mercury’s surface closeup on three flybys. In 2011, NASA’s Mercury MESSENGER became the first and only mission thus far to enter orbit around Mercury mapping and exploring the planet until April 30, 2015, when it became the only human artifact to impact Mercury.

BepiColombo will take up the mantle of Mercury exploration in the coming years, probing the planet from its core to its magnetic field and tenuous exosphere. The surface seen by previous missions shows signs of ancient volcanic activity and heavy bombardment. Could Mercury be the remnant of a planetary core that sustained a major impact early on in the solar system’s history? Is there any volcanic activity or outgassing today? ESA’s BepiColombo team hopes to answer these questions and more.

Looking far into the future, Rosocomos even has tentative plans for a Mercury lander named Mercury-P sometime in the 2030s. The usual cadence for planetary exploration is flyby, orbiter then lander, and such a mission would build on our understanding of previous missions such as BepiColombo.

We’ll be sure to follow this intriguing mission, as ESA’s BepiColombo makes a convoluted journey to Mercury.