Monday, August 4, 2008

The Case Against Pluto

Pluto's existence is dark and lonely, on the distant fringes of our Solar System. With a diameter of 2300 Km (1429 miles), Pluto is only 18% the size of Earth and much smaller than our own Moon.
For various reasons, Pluto is no longer even considered a planet.This is because it inhabits a section of space known as the Kuiper Belt, which is filled with objects like Pluto. In fact, Pluto isn't even the largest object in the Kuiper Belt. Downgrading its status from "planet" to "object" has created a storm of controversy.

In spite of this diminished status, scientists will soon be learning more about this mysterious body as the New Horizons spacecraft approaches its dark, frozen surface.

The planets from Venus to Saturn are visible to the naked eye, and have therefore been known since ancient times. The discovery of Uranus (in 1781) and Neptune (1846) heralded a search for other planets in our immediate neighborhood, and a quest for a better understanding of our region of space.

Pluto was first identified by American astronomer Clyde William Tombaugh in 1930, using the Lowell Observatory (left) in Flagstaff, Arizona. Variations in the gravity of the outermost planets had suggested to scientists that there was a ninth "Planet X" in the vicinity. After years of painstaking observations, he was able to photograph Pluto and its tiny moon, Charon. The dwarf planet was named by 11-year-old Venetia Burney, after the god of the underworld who had the ability to make himself invisible.

But Pluto was strange from the beginning: not only is it much smaller and more distant than the other planets, its satellite Charon is almost half the size of its host planet. In fact, the two bodies are almost like twins orbiting each other.

It's also a renegade because of the eccentricity of its orbit. While none of the planets' orbits are perfect circles, for the first eight planets the eccentricity is very slight. Pluto's orbit is actually egg-shaped; making it 7,380 million Km (4,586 million miles) from the Sun at its apogee, and only 4,447 million Km (2,763 million miles) at its nadir. In fact, its orbit is so unusual that for much of its life it actually orbits closer than the planet Neptune.

The Kuiper Belt is composed of debris left over from the formation of the Solar System. Scientists have discovered several other objects in the Kuiper Belt which are the same approximate size as Pluto, including the whimsically named planetoid "Xena", with its own satellite "Gabriella". This is what ultimately caused Pluto to be dropped from the most exclusive club in the Solar System. 

If it is indeed a "planet", then there are at least five (and possibly dozens or even hundreds) of other "planets" on the edge of our system beyond Neptune.

The image to the right is a photo of Pluto and Charon taken by the Hubble Space Telescope, and is our clearest picture of Pluto to date. In January 2006, NASA launched the New Horizons probe, about the size and weight of a baby grand piano. It's the fastest moving space vessel ever built, passing the Moon only 9 hours after launch (the Apollo missions took 3 days to reach the Moon).

New Horizons will reach Pluto after traveling for almost ten years, and will hopefully send us exciting new information about our distant, icy neighbor. Planet or not, Pluto has earned a place in the public imagination, and will soon be teaching us more about the most distant reaches of outer space.

For my previous posts on astronomy, click here.

For more information on Pluto and the New Horizons voyage, check out NASA's homepage. Included is a dazzling fly-by of the planet Jupiter.


Crazy Sam said...

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Hansisgreat said...

Thanks for checking in, Crazy.