A NASA space probe called New Horizons, launched more than nine years ago, is approaching Pluto. In a New York Times column yesterday, science writer Dennis Overbye looked back at exploratory missions to other planets, beginning with Venus in the early 60s, and made this remark: “the inventory of major planets — whether you count Pluto as one of those or not — is about to be done. None of us alive today will see a new planet up close for the first time again.”
As I said when I quoted his remark on Twitter, this isn’t certain but is probably true, and it’s rather heart-tugging. Overbye’s conclusion can be questioned on a technical basis; as another Times article reminded me, a few large objects have already been discovered in the Kuiper belt, and some scientists speculate that an object of a few Earth masses in size is circulating in that belt—there may, in other words, be more things we’ll come to call planets. And as Overbye suggests, Pluto itself has been reclassified, from full-fledged planet to what the IAU calls a dwarf planet, so in one sense we’ve already finished visiting all the major planets. Nonetheless, Pluto is included in what most people think of as the planets of our solar system. Some of them we could see in the night sky (and still can, despite the depredations of light pollution), others we could only be told about or shown on a diagram, but since school days we’ve known about all of these objects that in some sense are like the Earth, and many of us were taught mnemonics to preserve their order. From Mercury to Pluto, these are our neighbors; whether we think of them often or hardly ever, we all recognize their names. It’s surprising, even breathtaking, to think that, since I was born, a little more than half a century ago, mankind has managed to send scientific instruments to every one of them. Nine planets, and soon (barring an unlikely accident) we’ll be able to say that we’ve gotten a good look at all of them.
That’s a threshold of some sort, yet it’s no conclusion. In pondering this point we’re reaching I recall a line from Eliot’s Little Gidding: “We shall not cease from exploration.” As Eliot also wrote in that poem, “to make an end is to make a beginning.” We will go on from here. We have learned much; much remains to be learned.
I’m a little disappointed that Overbye omits the Soviet Union’s role in early planetary exploration and that he also sidesteps the work of other countries in exploring what he calls “the supporting cast of solar system characters.” But on the whole I admire his evocation of this grand period we’ve been living in. It has been, as he suggests in his conclusion, quite a ride.