The Rise of the Dwarf Planets
February 18th is the 82nd anniversary of the discovery of Pluto, the dwarf planet. The find was made in 1930 by an observer at Lowell Observatory in Arizona by the name of Clyde Tombaugh. He had spent months searching through and comparing photographic plates of the sky, looking for a possible new planet. His discovery was confirmed, and the name Pluto was bestowed on March 24, 1930. I had the pleasure to meet Clyde at a conference some years ago, when he spoke enthusiastically about his work to uncover this distant, frozen world.
Pluto is classified as a dwarf planet — which means it’s a special class of planet, much as white dwarfs are special classes of stars, and some galaxies are termed “dwarfs” based on the characteristics that differentiate them from spiral, elliptical, and irregular galaxies.
One of the fascinating things (among many) about Pluto is that its discovery really opened up a new phase of solar system exploration, resulting the discovery of more dwarf planets in the outer solar system.
Granted, we’ve done quite a bit of solar system exploration since Clyde’s momentous discovery. We’ve sent probes to most of the other planets, and studied them with ground- and space-based telescopes. But, until recently, we didn’t have the technical wherewithal to do more than study Pluto from Earth (or Earth orbit, with Hubble Space Telescope, for example). That changed when the New Horizons spacecraft was launched in 2006 on an voyage of exploration of the outer solar system.
New Horizons will arrive at Pluto in 2015. It will study the planet’s atmosphere, surface characteristics, and its nearest moons. After that, it will continue out to other outer solar system objects — in fact, its larger mission is to study the Kuiper Belt, a region of space that extends out from the orbit of Neptune and in which Pluto orbits . It’s really the gateway to all the outer solar system worlds, including Pluto.
I mentioned that astronomers have found other icy worlds out in Pluto’s domain, and beyond. Eris is the most massive known dwarf planet (so far), and orbits the Sun out well beyond Pluto. It’s an icy world roughly the size of Plut0. Then, there are Makemake, Haumea, Charon, Orcus, Quaoar, and Sedna. They’re all smaller and more distant than Pluto, but there’s no doubt they’re worlds in their own right. Undoubtedly others are out there, making trans-Neptunian space a sort of new frontier. This is why I see Pluto’s discovery as momentous. So, in celebration of Pluto Discovery Day, I raise a toast to Clyde Tombaugh — whose ashes are aboard the New Horizon spacecraft bound for Pluto space. Not only did he discover a dwarf planet, but he also opened the gates to discoveries in a sector of the solar system once thought empty and barren. It’s a bigger solar system than we thought, folks, and we have visionaries like Clyde to thank for helping us figure that out.