BepiColombo to swing by Mercury for the sixth time

BepiColombo is more than six years into its eight-year journey to planet Mercury. In total, it is using nine planetary flybys to help steer itself into orbit around the small rocky planet: one at Earth, two at Venus, and six at Mercury. Making the most of this sixth close approach to the small rocky planet, BepiColombo’s cameras and various scientific instruments will investigate Mercury’s surface and surroundings.  

BepiColombo will approach on the night side of the planet. Its monitoring cameras will get the most interesting views of Mercury’s surface as the spacecraft comes around to the planet’s sunlit side, from about 07:06 CET, seven minutes after the closest approach. We expect to release the first images on 9 January, with other scientific data to follow.  

“We can’t wait to see what BepiColombo will reveal during this sixth and final flyby of Mercury. While we’re still two years away from the mission’s main science phase, we expect this encounter to provide us with beautiful images and important scientific insights into the least-explored terrestrial planet,” says Geraint Jones, ESA’s BepiColombo Project Scientist. 

Warming up for Mercury’s shadow 

While Mercury’s sunlit side is scorching, the first part of the upcoming flyby will be spent on Mercury’s cold, dark night side. While in Mercury’s shadow, BepiColombo will not receive any direct sunlight for more than 23 minutes and will rely only on its batteries. 

Mission operators at the European Space Operations Centre (ESOC) are gearing up for this critical moment of the flyby. One day ahead of the eclipse, they will warm up the spacecraft and only stop the heating a few minutes before BepiColombo enters Mercury’s shadow. This operation will help save battery power by ensuring that the spacecraft does not need to use its heaters during the eclipse. 

“This is the first time BepiColombo stays in the shadow of Mercury for so long. We have fully charged its batteries and raised the temperature of all components. From ESA’s mission control centre, we will keep a close watch on the battery status and the temperature of all systems during the flyby,” says Ignacio Clerigo, BepiColombo’s Spacecraft Operations Manager. 

The Italian Spring Accelerometer (ISA) will record the accelerations felt by the spacecraft as it experiences not only the gravitational pull of the planet, but also the change in solar radiation and temperature as the spacecraft enters and exits Mercury’s shadow. ISA will also record any movements and vibrations of the spacecraft caused by the motion of, for example, the spacecraft’s solar arrays. 

Key views of Mercury’s shadowy north pole

Excitingly, BepiColombo’s route takes it right over Mercury’s north pole. This allows the spacecraft to peer down into craters whose insides never get touched by the Sun. Despite temperatures reaching 450 °C on Mercury’s sunlit surface, the polar ‘permanent shadow regions’ are literally ice-cold.  

Data gathered by instruments on NASA’s Messenger spacecraft between 2011 and 2015, plus radar observations from Earth, have provided strong evidence for water ice in some of these craters. Whether there is really water ice on hot Mercury is one of the top five mysteries that BepiColombo has set out to solve. 

During this flyby, BepiColombo’s monitoring camera 1 (M-CAM 1) should get some nice views of the permanently shadowed Prokofiev, Kandinsky and Tolkien craters. 

Other exciting features that BepiColombo’s monitoring cameras will see are the deep Stieglitz and Gaudí craters, Mercury’s largest impact crater (the more than 1500 km-wide Caloris Basin), and the vast northern plains known as Borealis Planitia.  

Below is a simulation of M-CAM 1’s views of Mercury during the flyby, using a digital topography model prepared by the Messenger mission team. There is a gap in this model around the poles. BepiColombo’s upcoming flyby views, and the mission’s polar orbits around Mercury from 2026, will greatly improve the coverage in these regions. 

More insight into Mercury’s surroundings

BepiColombo’s sixth flyby also takes it on a unique route through Mercury’s magnetic and particle environment. The spacecraft will fly through regions around Mercury that haven’t been sampled before and parts of which won’t be visited by BepiColombo during the main science phase of its mission.  

The upcoming flyby route, crossing the equator opposite the Sun on Mercury’s night side before flying over the planet’s north pole, makes it particularly interesting. In darkness, the spacecraft will pass through regions where charged particles can flow from the planet’s magnetic tail towards its surface. At the poles, in regions called the cusps, planetary magnetic field lines also funnel particles coming from the Sun down to Mercury’s surface. The spacecraft will pass through the northern cusp. 

Two particle analysers (SERENA and MPPE) will ‘taste’ the particles in these fascinating regions, parts of which won’t be visited when orbiting the planet. Meanwhile, two magnetometers (MPO-MAG and MMO-MGF) will sense Mercury’s magnetic field, while a dust monitor (MDM) will measure larger dust particles. (Read more about BepiColombo’s science instruments on ESA’s Mercury Planetary Orbiter and JAXA’s Mercury Magnetospheric Orbiter.) 

This will build on measurements taken during BepiColombo’s earlier Mercury flybys, as well as by NASA’s Messenger mission.

About BepiColombo

Launched on 20 October 2018, BepiColombo is a joint mission between the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA), executed under ESA leadership. It is Europe’s first mission to Mercury.  

The mission comprises two scientific orbiters: ESA’s Mercury Planetary Orbiter (MPO) and JAXA’s Mercury Magnetospheric Orbiter (Mio). The European Mercury Transfer Module (MTM) carries the orbiters to Mercury.   

After arrival at Mercury in late 2026, the spacecraft will separate and the two orbiters will manoeuvre to their dedicated polar orbits around the planet. Starting science operations in early 2027, both orbiters will gather data during a one-year nominal mission, with a possible one-year extension.  

All M-CAM images will be made publicly available in the Planetary Science Archive. 

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