February 4, 2011

Happy Birthday, Clyde Tombaugh

How would you like to be the first person to discover a dwarf planet? How’d you like to be the only person in the twentieth century to discover a planet? How about being the one who discovers the first Kuiper Belt Object?

Clyde Tombaugh, who was born on this day in 1906, got to be all three…all because he discovered Pluto!

During Tombaugh’s lifetime, Pluto was considered the ninth planet.

Because of recent discoveries of many other objects from as far away as the orbit of Neptune out to 55 A.U. from the sun, astronomers decided that Pluto was just a large-sized example of an rocky/icy body in an entire wide belt of rocky/icy bodies. This belt is called the Kuiper Belt, and so Pluto is now considered a Kuiper Belt Object (KBO).

When I say that there are “many” KBOs…I’m talking thousands! There are more than 70,000 KBOs that are larger than 100 km (62 miles) in diameter. Several of these KBOs are large enough to be considered dwarf planets: Eris (which is larger than Pluto), Pluto, Haumea, and Makemake. Some of the moons of planets (such as Neptune’s Triton and Saturn’s Phoebe) are considered to have once been KBOs, and the dwarf planet Pluto has a relatively large moon, Charon, plus two smaller moons, Nix and Hydra, that are of course also KBOs.

So Pluto was a planet and is now a Kuiper Belt Object and a dwarf planet—and Clyde Tombaugh’s guarantee of inclusion in the history books.

By the way…

Another name for a dwarf planet that is in the Kuiper Belt is plutoid. So we could also say that Tombaugh discovered the first plutoid!

Tombaugh was just 24 years old when he discovered Pluto.

Tombaugh wanted to go to college, but hailstones ruined his family’s crops and spoiled his hopes for being able to afford it. He didn’t give up! He built several telescopes, grinding the lenses and mirrors himself, and he sent drawings of Jupiter, Mars, and the telescopes to the Lowell Observatory in Arizona. This bold move resulted in Tombaugh being offered a job in 1929. It was on the job as an astronomer that Tombaugh made his big discovery.

After discovering Pluto, Tombaugh was able to finally go to college (apparently while still keeping his job). He ended up getting both a bachelor’s and a master’s degree in astronomy.

Tombaugh discovered nearly 800 asteroids, a comet, hundreds of variable stars, star clusters, galaxy clusters, and a galaxy supercluster.

Tombaugh helped to choose the name Pluto, but he didn’t think of the name himself. Instead, a little girl, age 11, who lived in far-away England, made the suggestion… Venetia Katharine Douglas Burney was excited about the discovery of a ninth planet and suggested the name Pluto, who was the Roman god of the underworld. It seems that Burney made that particular suggestion partly because the other planets are named for Roman gods and partly because Pluto-the-god had the power to turn himself invisible—and Pluto-the-planet had been so hard to discover, it was as if it had the power of invisibility.

One reason Tombaugh liked and chose the name Pluto is because the first two letters, P and L, are the initials of the astronomer who predicted that there would be a planet beyond the orbit of Neptune. Percival Lowell was a wealthy man who founded the observatory in which Tombaugh worked and who urged the search for “Planet X,” which, Lowell claimed, slightly displaced both Uranus and Neptune from their orbits. Unfortunately, Lowell died at age 61, fourteen years before Planet X was discovered and named Pluto.

Pluto has four known moons.

Poor Pluto?

A lot of people seem to be upset that Pluto has been “demoted” from being a planet to being a mere dwarf planet. They seem to feel hurt on behalf of poor Pluto, as if they were worrying about the feelings of Mickey Mouse’s beloved dog Pluto. (By the way, the Disney pup Pluto was named after the planet/dwarf planet—the whole world was excited by its discovery!)

If you worry about poor Pluto, read this clear and accurate explanation why the new label for Pluto as a dwarf planet is better science.

Remember, as Fraser Cain clearly points out in the link above, one of the recently discovered Kuiper Belt Objects is larger than Pluto. If Pluto were to still be considered a planet, Eris would have to be, too. No matter what, we can’t hold onto a solar system with nine planets—at this point, we can either have 8 or we can have 10, 12, or more—depending on where you draw the cut-off line of size between planets and dwarf planets. Astronomers have decided on a good, solid definition for planet that dictates that the solar system has 8 planets.