This is what Pluto looks like.
The New Horizons spacecraft, launched 2006 Jan. 19, will around noon today hurtle past Pluto at a distance of about 12,500 kilometers (7,800 miles) and a speed of 45,000 km per hour (28,000 mph).
On the way, the spacecraft passed an asteroid called 132524 APL, then on 2007 Feb. 28 got a gravitational boost toward Pluto by whipping around Jupiter. Getting nearer to Pluto, it revealed that the dwarf planet has cliffs and canyons larger than the Grand Canyon, and an icy northern cap, and a diameter of 2,370 kilometers (1,473 miles), rather wider than some previous estimates, so that it must be less dense and have more ice (the Moon is 3,474 km wide); and on Sunday (July 12) at a distance of a million miles New Horizons took this photo. Fuller data will come tomorrow afternoon when the craft reports back after its passage. If it survives – collision with a near-Pluto particle the size of a rice grain could destroy it.
When Pioneer 10 and 11 and Voyager 1 and 2 were launched in the 1970s for their “Grand Tour” of the outer planets in the 1980s, this was made possible by the grand curve that had happened to come about: Neptune ahead of Uranus ahead of Saturn ahead of Jupiter, each allowing a gravitational slingshot onward to the next. Pluto, then considered an outer planet too, was left out because it was far behind this curve. (One day I will try to get the several diagrams I have made of this, in the Astronomical Calendar and Companion, printed as a poster.) So now we have the first visit to Pluto.
I remind you of the idiot story of why Pluto, now classified as a dwarf planet like the largest asteroid 1 Ceres, has an unrememberable official number. The late Brian Marsden, a magisterial scientist and a wise and courteous gentleman, keeper of the records for the International Astronomical Union, foresaw that Pluto would have to be downgraded from the status of major planet; the numbering of minor planets (asteroids) was growing toward 10000, so he suggested that this number should be reserved for Pluto. This would have kept it at the head of the list of trans-Neptunians, the others like Eris not yet having been numbered. His suggestion didn’t necessarily imply downgrading Pluto yet, but because of opposition to that possibility it was rejected by the IAU. Result, when Pluto was downgraded some years later, it became minor body number 134340.