Bepi-Colombo is scheduled to be only the second mission to orbit Mercury, the Sun’s innermost planet. But getting there hasn’t been easy. The craft has made eight close passes by Earth, Venus, and Mercury to slow itself against the Sun’s powerful gravity. And it’ll make its final close approach to Mercury tomorrow.

Bepi-Colombo actually consists of two probes that are linked up. When they enter orbit around Mercury they’ll split apart. One of them will make a detailed map of the surface. The other will map Mercury’s magnetic field. The observations will tell us much more about how the planet is put together, what it’s made of, and how it’s evolved.

Mercury is about half-again the size of the Moon. And its surface looks a lot like the Moon’s – big impact craters, rugged mountains, and tall cliffs. But Mercury’s innards are quite different from the Moon’s. The planet has a large core of iron and nickel. So as Mercury turns on its axis, it generates a magnetic field. The field traps particles of the solar wind, giving Mercury a very thin atmosphere.

Bepi-Colombo was supposed to enter orbit around Mercury late this year. But in April it had a problem with its thrusters. So flight controllers worked out a new final approach to Mercury. That will delay its arrival until late 2026.

For now, though, Bepi-Colombo will aim its instruments at Mercury as it makes one final close pass by the Sun’s closest planet.

Script by Damond Benningfield