Pluto the Outcast

pressable October 12, 2012

I recently attended an Astronomy and Astrophysics Public Lecture, which are held every month by our Physics and Space Sciences department. Dr. Oswalt gave a talk titled, “How I Helped Kill Pluto and Why It Had It Coming” in which he discussed the process humans have gone through while discovering what comprises our solar system and made a case for why he support the decision to vote Pluto out of the planet status.

The most basic model of our solar system includes the Sun with four terrestrial and four Jovian planets orbiting around it. The solar system has pretty much been that way since the mid-1800s. However, just like Neptune was discovered by observations of slight disturbances in Uranus’ orbit, Neptune’s orbit was a bit off, setting off the search for “Planet X.” Finally in 1930, Pluto was discovered. The discovery was made by Clyde Tombaugh (in the employ of Vesto Slipher) at the Lowell Observatory. His job consisted of taking two pictures, each a week apart, and with a machine called a blink comparator, he would rapidly switch back and forth between the pictures to see if any objects had moved. Although rather tedious, it eventually bore fruit.

The newly discovered object (coined “Pluto” by 11-year-old Venetia Burny) was accepted worldwide as a new planet. Pluto’s first moon, Charon, was discovered in the late 1970s when a strange bump was observed to appear and disappear on opposite sides of the blurry, pixelated images of Pluto every six days. More moons were not detected until 2006, when Nix and Hydra were found with the help of Max Mutchler a Florida Tech alumnus! Then in July 2012, two more moons were discovered by blocking out the brightness of Pluto and Charon; these moons have not even been named yet and are only known as S/2011 1 and S/2012 2.

Surely with all these moons, Pluto must be a planet, right? The real problem, actually, is there really was not a specific definition for what a planet was. Observations cannot be ignored, however; Pluto does not fit in with the other eight planets. While the other eight follow the predicted pattern of a solar system capable of growing life (with small, rocky planets close to the star and giant, gaseous planets further away), Pluto is pretty much a giant ice chunk, based on its composition spectrum, which tells us Pluto is covered in methane ice. Also, Pluto’s orbit is very eccentric, especially compared to the nearly circular orbits of all the other planets, and Pluto strays far from the plane of the solar system, much like a comet does.

The real clincher, however, was when the search for trans-Neptunian objects (TNOs) began – and more and more objects just like Pluto were found. If Pluto is a planet, then at least 43 other objects beyond Pluto (in the region called the Kuiper Belt) should also be planets. Because of the vast differences in composition, orbits, sizes, and distances, these TNOs (or more accurately Kuiper Belt Objects, KBOs) needed to be classified differently than our terrestrial and Jovian planets. So as of 2006, “dwarf planet” is the current term used for objects like Pluto.

Pluto’s demotion does not mean we’re done with the little ice ball. By no means! Right now the space craft New Horizons is headed for Pluto and by 2015 we will finally have our first close-up pictures. The best images we have of Pluto right now are images from the Hubble Space Telescope, which reveal it to have black, orange, and white regions, as shown below. We aren’t sure why its surface looks so varied, and it will be an exciting day when clear images come back to us from New Horizons!