Mercurial Encounter

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Mercurial Encounter

A spacecraft that’s scheduled to enter orbit around Mercury in late 2025 will tap the brakes tomorrow. It’ll fly past Mercury, using the planet’s gravity to slow it down a bit. It’ll take a peek at Mercury as it speeds by.

BepiColombo is a European mission. It consists of two separate spacecraft that are linked up for the ride. Once they arrive at Mercury to stay, they’ll go their own ways, following separate orbits around the planet. One of them will probe Mercury’s interior and its surface, while the other monitors the planet’s magnetic field.

Entering orbit around Mercury is tough. Mercury is the closest planet to the Sun, so a craft can use the Sun’s gravity to pull it inward. The problem is, that gravitational pull is too strong, so falling toward the Sun is like rolling down a steep hill. A craft really needs to ride the brakes to slow down enough to enter orbit.

There are a couple of ways to do that. One is to carry a big honkin’ rocket engine. But that’s expensive. The other is to use the gravity of the planets. If you target a craft just right, the planet exerts a slight “drag” on it, slowing it down.

BepiColombo flew past Earth once and Venus twice. And tomorrow, it’ll make its third pass by Mercury. Even with all of that, it’ll need three more encounters to get it just right — to slow down enough to enter orbit and begin exploring the Sun’s closest and smallest planet.

Script by Damond Benningfield

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