BepiColombo: First Rendezvous with Mercury First measurement of the magnetic field of Mercury's southern hemisphere

After the Venus flyby in August 2021, BepiColombo is targeting the next planet: On October 2, 2021, the satellite will reach Mercury, the actual destination of its journey. Until the mission is completed, it will make a flyby several more times until it enters Mercury’s orbit. The excitement at Technische Universität Braunschweig is particularly high because the satellite is equipped with TU measurement technology. New data can be collected from an unexplored site: the southern hemisphere.

On October 2, 2021, the BepiColombo spacecraft will make a flyby of its target planet, Mercury. By December 2025, the maneuver will be repeated five more times to gain momentum for the destination flight in the most fuel-efficient way possible: After this precision work, BepiColombo will reach Mercury’s orbit. During the flyby, the magnetometers developed at the Institute of Geophysics and Extraterrestrial Physics (IGEP) at TU Braunschweig are permanently activated.

Then the researchers led by Dr. Daniel Heyner, who heads the magnetometer team at IGEP, will be able to evaluate the first of their own data from Mercury’s magnetosphere. So far, only the Northern Hemisphere has been magnetically surveyed by NASA’s MESSENGER mission. “It’s like having just explored North America and seeing South America through binoculars, but unfortunately having to abort the expedition. As a researcher, you’re naturally curious and desperate to go back,” says Dr. Heyner. That makes this flyby particularly interesting, as it is the first time that data from the planet’s southern hemisphere is available – even if it is just a small sample.

Can the characteristics of the magnetic field from the northern hemisphere be easily transferred to the southern hemisphere? Has the magnetic field generated by the dynamo perhaps even changed in the last six years after the last NASA mission – as it continuously does on Earth? These are currently the burning questions on the minds of the Braunschweig researchers. For this purpose, the new magnetic field data are compared with global models based on the NASA data. These global models can be thought of as magnetic maps. In the case of Earth, the maps have continued to improve over time and become more accurate. Now, to find out what geophysical processes are taking place inside Mercury, we need the most accurate magnetic map possible.

What will happen after the Mercury flybys?

BepiColombo consists of three components until it is launched into its final orbit: Mercury Planetary Orbiter (MPO), Mercury Magnetospheric Orbiter (MIO) and Mercury Transfer Module (MTM). Shortly before reaching the target orbit, the transfer module is separated, and shortly thereafter the two probes MPO and MIO also separate from each other, continuing their journey in different orbits around Mercury, which is close to the Sun. In the process, they are not only exposed to high temperatures (300 degrees Celsius). During the primary mission, which will last about a year, the satellites will also have to withstand solar radiation and infrared radiation – emitted by Mercury’s surface, which has a temperature of up to 470 degrees Celsius. When the satellite enters Mercury’s shadow, there is a rapid change to very cold temperatures. It will be the first time that a planet other than Earth has been surveyed simultaneously with two satellites.

Goals of the magnetometer measurements

This dual approach has the advantage of simultaneously measuring the solar wind in front of Mercury with MIO and Mercury’s magnetosphere with the MPO satellite. This allows us to see how the magnetosphere responds to solar storms, for example. At Mercury, these massive particle ejections cause the magnetosphere to oscillate. Sometimes these solar storms are so violent that the magnetosphere collapses, leaving the planet “naked” in the solar wind because it lacks a magnetic shield. However, the declared main goal of the Braunschweig researchers remains to complete the magnetic map of the planet as precisely as possible. “Of course, such precision requires sophisticated sensor calibration,” emphasizes Dr. Ingo Richter, who runs the calibration laboratory in Braunschweig. This magnetic field map can then be compared with dynamo models that were also created at IGEP. This then allows important conclusions to be drawn about the long-term thermal evolution of Mercury.

Close European-Japanese cooperation

The overall management of the mission lies with the European Space Agency (ESA), which was also responsible for the development and construction of the Mercury Planetary Orbiter (MPO). The Mercury Magnetospheric Orbiter (MIO) was contributed by the Japanese space agency JAXA. This second satellite is also equipped with magnetometers, for which IGEP cooperates with Japanese institutes. The German contribution to BepiColombo is predominantly financed by DLR Space Management with funds from the Federal Ministry for Economic Affairs and Energy (BMWi).