BepiColombo orbiters separate ahead of Mercury arrival; Strofio to sample exosphere
The European-Japanese BepiColombo mission has released its two orbiters from the transfer module, clearing the way for Mercury orbit insertion in November 2026. NASA's Strofio instrument, built by Southwest Research Institute, will measure Mercury's exosphere to map surface composition from orbit, offering a global view impossible from a lander.
Bottom line — BepiColombo becomes only the second mission to orbit Mercury, with Strofio data expected to reveal surface composition and origin clues.
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- The orbiters separated last week, removing protective covers from Strofio, per Southwest Research Institute (SwRI).
- Strofio is a basketball-sized neutral mass spectrometer weighing just over 3 kg, designed to sample sparse exosphere particles kicked up by meteor impacts and solar wind, the institute said.
- Orbiting Mercury is harder than Jupiter: solar gravity accelerates the craft, requiring multiple gravity assists from Earth, Venus, and Mercury over nearly 10 years, versus 4-5 months for a flyby, per SwRI.
- Mercury's weak gravity sustains only a tenuous exosphere; Strofio will measure surface material globally, unlike a lander that would sample one site, explained SwRI's Dr. Frederic Allegrini.
- SwRI's Jared Schroeder said the team hopes to clarify Mercury's surface composition and its interaction with the exosphere, potentially answering questions about the planet's origin.
- The mission, launched in 2018, is named after Italian scientist Giuseppe Colombo, whose gravity-assist calculations enabled Mercury encounters, per SwRI.