BepiColombo Is Eight Years In and Finally Closing In on Mercury

Eight years is a long time to wait. But then again, getting to Mercury is not easy. The planet sits so close to the Sun that reaching it requires an extraordinarily complex series of gravitational assists, looping around Earth, Venus, and Mercury itself multiple times to bleed off enough energy to enter orbit without getting flung back out into space or swallowed by the Sun's gravity. Europe's BepiColombo mission has been doing exactly that since its launch in 2018, and as of September 2026, it is finally on its final approach to its destination.

BepiColombo is a joint mission between the European Space Agency and the Japan Aerospace Exploration Agency, and it is carrying two separate science orbiters: ESA's Mercury Planetary Orbiter and JAXA's Mercury Magnetospheric Orbiter. The two spacecraft have been travelling together in a stacked configuration, a Mercury Transfer Module sandwiched between them, providing propulsion and power for the cruise phase of the journey.

Why Mercury Matters

Mercury is one of the least studied planets in the solar system relative to its proximity to Earth. That seems counterintuitive until you try to understand how difficult it is to get there. The same gravitational well that makes it hard to visit also makes it scientifically fascinating.

The planet is far denser than models of its formation predict it should be, suggesting it has an unusually large iron core relative to its total size. One leading theory is that Mercury was once a much larger planet whose outer layers were stripped away by a catastrophic collision early in the solar system's history. Another is that the intense heat and radiation from the Sun drove off lighter materials during formation. BepiColombo's instruments are designed to help settle that debate.

The mission's science teams have described their core question clearly: they want to understand the origins of Mercury and how it came to be the way it is. That sounds simple, but answering it requires detailed measurements of the planet's surface composition, its magnetic field (which is surprisingly active for such a small planet), its exosphere, and its geology. BepiColombo's twin orbiters will study all of these from complementary orbits once they separate after insertion.

What Happens Next

Mercury Orbit Insertion is now the critical event on the timeline. The spacecraft needs to fire its engine at precisely the right moment to slow down enough to be captured by Mercury's gravity rather than skipping off into space. After eight years of travel, the margin for error is essentially zero.

Once in orbit, the two science craft will separate and move into their respective operational orbits. The Mercury Planetary Orbiter will take up a highly elliptical orbit that takes it from about 480 kilometres above the surface to around 1,500 kilometres at its highest point, which is close enough to image the surface in high resolution. The Mercury Magnetospheric Orbiter will work from a more polar orbit, focusing on the planet's magnetic environment.

The science phase is expected to last at least one Earth year, with a possible extended mission if the spacecraft remain healthy. Given that the planet's surface temperatures swing from minus 180 degrees Celsius on the night side to over 430 degrees Celsius in full sunlight, keeping delicate instruments functioning is no small achievement.

Why This Matters Right Now

We are at an interesting moment for planetary science. NASA's Artemis programme is focused almost entirely on the Moon, and Mars gets the lion's share of media attention. Mercury sits in a strange position: too difficult and expensive to visit regularly, but scientifically important enough that the answers BepiColombo brings back could reshape our understanding of how terrestrial planets form.

If it turns out that Mercury's unusual density is the result of a giant impact early in the solar system, that has implications for how we model planet formation everywhere, including around other stars. The data coming from this mission over the next year or two could be some of the most important planetary science of the decade, even if it never quite gets the headlines that a Mars sample return or a crewed lunar landing would.