In Bastille Day, the human race will visit the final planet – or ex-planet. The fastest-ever spacecraft was launched in 2006, fast-tracked for a rendezvous with the most controversial world. Finally, next week, it arrives – or rather, speeds past. The New Horizons spacecraft will not stop to orbit; it will merely continue outward into the cold lonely depths of space, cameras clicking. At its closest Tuesday morning, it will skim just one Earth-diameter above Pluto’s surface. Its window of close-approach will only last about a half-hour.
Meantime, by sheer coincidence, this Monday (July 6), Pluto arrives at its closest and brightest of the year. That’s not good enough. It’s too dim to appear in the finest binoculars. Even a large amateur telescope merely shows it as a faint speck in Sagittarius, and you’d need a super-accurate star chart to distinguish it from the zillions of other faint dots just to the left of our galaxy’s center. Pluto shines feebly at 14th magnitude. It’s 600 times fainter than the dimmest naked-eye stars.
It’s dim because it’s not just far away; it’s tiny – roughly half the size of our Moon. But it’s not an “it”; it’s a “they.” There are two of them, dual balls with a mere two-to-one size difference: Pluto and Charon (pronounced like the feminine name Karen). The pair orbit around an empty piece of space between them, once a week. Both worlds rotate, too, so that just one hemisphere of each always faces the other, eyeball-to-eyeball. A few other tiny moons are there too, with names like Nyx.
Pluto’s orbit is more than twice as tilted as any other, which carries it into odd places in the nightly heavens. It’ll still dwell in traditional zodiac constellations until 2060, but then it will move into Cetus the Whale, where it will lurk for more than a half-century.
No spacecraft has ever visited Pluto’s frozen surface, but now we will suddenly see features for the first time. Mountains? Craters? Or will it just be a flat, blotchy ice surface? We’re about to find out.
As we all know, in 2006 the International Astronomical Union (IAU), the world body that decides such things, demoted Pluto to a “Dwarf Planet.” This produced howls of protest that will probably get reamplified next week. Pluto remains a popular world, and the public is unhappy with the decision to demote it from the ranks of major planets.
We’ll get into that and more next week. Meantime, like Mickey, we’re all about to say or think, “Hello, Pluto!”