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The path of BepiColombo.

(Science Week, Day 5!)

Speaking of astronomical frontiers in 2025, the BepiColombo probe remains on en route to Mercury – though, arguably, “en route” might imply it’s heading directly for the planet, and that’s far from true.

This is an incredible aspect of intraplanetary travel for probes: the deliberate use of planets’ gravity fields to steer and direct their course as desired. Memorable examples include Voyager 1 and 2, travelling outward from Earth toward deep space, using the gas giants as slingshots between each other by almost falling to their surface, but not quite; enough to veer and pick up significant speed while ultimately escaping their fields.

Apparently visiting our innermost planet comes with an immense challenge intrinsic to its inner-ness. The gravity of the giantest “gas giant” of all, the sun, is so immense that firing a probe straight at Mercury would be pointless: the speed at which the probe would be “falling” by the the time it reached the gray rock would doom its chances of entering orbit, to put it mildly. What’s needed is a gentle and synchronized convergence, like a car driving a guy smoothy up alongside a train who wants to shout an analogy at the engineer.

BepiColumbo’s solution is to make nine of these aforementioned fly-bys to cajole it into this gentler rendezvous. The first is, fascinatingly, with the Earth itself, and more than the last several are with Mercury itself; in fact, its first brush with Mercury this coming fall will occur several years before it’s softened into its ultimate approach.

The planning involved! And of course, the underpinning work stemming from Kepler, Newton and Einstein regarding gravity and planetary motion, to be crudely brief.

And along the way, images of these encounters for everyone to see.