BepiColombo’s Close‑up Scan of Mercury’s Solar Assault Reveals New Space‑Weather Clues

Eight years after launch, ESA’s and JAXA’s BepiColombo mission has already skimmed Mercury six times, each pass peeling back layers of mystery surrounding the smallest rocky world. From icy deposits at the poles to puzzling “hollows” in the crust, the twin orbiters have been busy.

One of the most striking experiments aboard the spacecraft is the Solar Intensity X‑ray and Particles Spectrometer, or SIXS, built by a team at the University of Helsinki. Their goal? To watch, in real time, how the Sun’s tempestuous outbursts batter a planet that lives practically on the solar furnace.

It was on September 4 2024, during BepiColombo’s fourth flyby, that the planet‑hugging probe dove to a hair‑raising 165 km (about 102 mi) above Mercury’s scarred surface. At that very moment the Sun erupted, hurling a wave of high‑energy charged particles straight toward the innermost planet.

“The fourth flyby was truly unique,” says Prof. Emilia K. J. Kilpua, the SIXS principal investigator, in a press release from Helsinki. “We were lucky enough that a major particle eruption happened right when we were at our closest approach.”

SIXS captured a deluge of particles that punched through Mercury’s modest magnetic shield and slammed into the regolith over a broad swath. When those energetic particles struck atoms on the surface, they set off a cascade of X‑rays—signatures that the instrument logged with impressive detail.

Why does this matter for Earth? Mercury’s magnetic field is far weaker than ours, and its magnetosphere is tiny. By watching how the solar storm seeped through that thin barrier, scientists can refine models of what would happen if a comparable eruption compressed Earth’s own magnetosphere. The stakes are high: severe solar storms can fry satellites, knock out power grids, and wreak havoc on any technology that relies on space‑based assets.

Co‑author Prof. Rami Vainio of the University of Turku adds, “These observations give us a laboratory for testing the worst‑case particle radiation scenarios that could affect Earth’s near‑space environment.” The data are already feeding into the Center of Excellence in Space Resilience, a program aimed at safeguarding low‑Earth‑orbit operations against extreme space weather.

Later this month the two BepiColombo modules—the Mercury Planetary Orbiter and the Mercury Magnetospheric Orbiter—will part ways from their shared carrier. By November they will slip into orbit around Mercury, and by December they will separate from each other, beginning a new chapter of close‑up exploration.

For anyone fascinated by how our star’s tantrums ripple across the solar system, the latest SIXS findings are a reminder that even the most diminutive planets can teach us big lessons about protecting our own world.