Mercury, the closest planet to the sun, is extremely difficult to study up close. In fact, just one spacecraft, NASA’s MESSENGER, has ever orbited the planet. But soon a second mission will begin exploring this rocky world to tease out new details about its surface, interior and interaction with our star. And on Thursday that mission—BepiColombo, a joint operation of the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA)—took a critical step closer to beginning in earnest.
After an eight-year voyage in space, BepiColombo’s two component science orbiters, which will together observe Mercury, have split off from the spacecraft’s Mercury Transfer Module: the ESA’s Mercury Planetary Orbiter and JAXA’s Mercury Magnetospheric Orbiter were released and gave out a strong signal to Earth, according to an ESA livestream of the procedure.
The job isn’t done yet. Now that they’ve separated from the transfer module, the Mercury Planetary Orbiter and Mercury Magnetospheric Orbiter will remain joined together until November, when they’ll enter orbit around Mercury. A month later, they’ll go on their separate orbital paths before full science operations begin next April.
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The ESA orbiter will gather data on Mercury’s topography and interior structure and will put Einstein’s general theory of relativity to the test, while the JAXA orbiter will study the planet’s magnetosphere and magnetic field.
BepiColombo has already had a couple of close interactions with Mercury: it conducted flybys that used the planet’s gravity to help it get toward the proper position to accomplish its mission. During one such flyby in 2021, the spacecraft captured some photographs of the surface from just 199 kilometers (123 miles) away.
An image taken by BepiColombo shows that large regions of Mercury’s heavily cratered surface are smoothed over by lava from volcanic eruptions.
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