On October 1, 2021, the combined European Space Agency and Japan Aerospace Exploration Agency BepiColombo spacecraft completed its first flyby of Mercury, the solar system’s innermost planet. The flyby is the first of six such occurrences that BepiColombo will perform before entering orbit around Mercury in late 2025.
Following the flyby, preliminary science results from several types of equipment onboard BepiColombo revealed intriguing facts about the atmosphere surrounding Mercury, as well as details about the planet itself.
BepiColombo’s first Mercury flyby sequence occurred on October 1 and October 2, with the closest approach coming on October 1 at a distance of 199 km from the surface of Mercury when the spacecraft’s monitoring cameras collected photographs of the planet.
These same cameras captured photographs of Venus during BepiColombo’s second flyby of the planet in August 2021. The three monitoring cameras onboard BepiColombo’s Mercury Transfer Module took photographs of the planet for four hours, commencing around five minutes after the closest approach.
While the images of Mercury are visually impressive with the planet seen behind some of BepiColombo’s instruments and stunningly clear, they also allow scientists to identify specific surface craters on the planet and marked the start of the craft’s scientific objectives at Mercury, as some regions around the planet will not be accessible once the craft enters orbit, so they must be studied during the flybys.
From the perspective of the spacecraft, the flyby was faultless, and it’s fantastic to finally have a glimpse at the targeted planet.
As the flyby continued, many equipment onboard BepiColombo’s modules collected data on Mercury and its surroundings. It may have been a brief flyby, but for several of BepiColombo’s sensors, it signaled the start of science data collecting and an opportunity to begin planning for the main mission.
These flybys also provide an opportunity to sample portions of Mercury that will be inaccessible once they are in orbit. The PHEBUS UV spectrometer on BepiColombo’s Mercury Planet Orbiter module acquired data on Mercury’s exosphere, which is an extremely thin, low-density atmosphere, during the flyby. The exosphere is now assumed to exist as a result of either solar wind or surface material.
PHEBUS studied the area for an hour. Following BepiColombo’s escape from Mercury’s shadow, PHEBUS detected significant concentrations of hydrogen and calcium. These two elements are considered to be prevalent in Mercury’s exosphere.
The Mercury Gamma-ray and Neutron Spectrometer instrument, which is also situated on the MPO, found intense fluxes of neutron and gamma-rays in the exosphere, which are frequently created by galactic cosmic rays interacting with a planet’s topmost surface layers.
Furthermore, these emissions might reveal information on the composition of Mercury’s surface. The BepiColombo research team is presently analyzing the MGNS data as well as the MGNS data from BepiColombo’s second Venus flyby in August.
Once in orbit around Mercury in 2025, PHEBUS and the MGNS will conduct in-depth studies of the planet’s exosphere, describing its composition and behavior. PHEBUS will also monitor changes in the exosphere’s position over time.
Because of Mercury’s near closeness to the Sun, one could anticipate the planet to be bombarded by solar wind expelled from the Sun’s corona regularly. Mercury’s magnetic field, like that of Earth, helps to protect the planet from the full power of coronal ejections.
Until BepiColombo’s flyby, only Mercury’s northern hemisphere had been magnetically scanned by a spacecraft, leaving scientists in the dark about how the planet’s magnetic field and solar wind interacted in the planet’s southern hemisphere.