Dwarf Planet Pluto - Arizona Trivia Tuesdays

Did you know that the object formerly known as a planet called Pluto (demoted, in 2006, to "dwarf planet" status) was discovered in 1930 at the Lowell Observatory in Flagstaff, Arizona?

The following is summarized from Wikipedia.org:

Neptune's existence was predicted in the early 1840's, before its first observation in 1846, because of disturbances in Uranus's orbit. Disturbances in Uranus' orbit that were not explained by Neptune led astronomers to predict the existence of yet another planet in our solar system, out beyond Uranus' orbit.

Percival Lowell searched until his death in 1916 for the planet, and in 1915, his observatory captured two faint images of Pluto, but no one recognized them at the time.

In 1929, Clyde Tombaugh, who at 23 years old was new to the Lowell Observatory, was appointed to conduct a systematic search for the planet, and he succeeded in February 1930.

The planet was officially named on March 24, 1930. It was not named after the Disney character, but after the god of the underworld in classical mythology. It is possible that the Disney character was named after the planet.

Over the years, estimates of Pluto's mass were repeatedly revised downward, until 2006 when it was finally demoted to "dwarf planet" status. [See footnote 1]

Additional interesting facts about Pluto:

* It takes 248 Earth years for Pluto to complete its orbit (i.e., for one "Pluto year"). That must be one heckuva long winter, right? Then again, it's so far from the sun that it is, for us, impossibly cold (approximately -230C) all the time anyway!

* It takes 6.39 Earth days for Pluto to revolve (i.e., for one "Pluto day").

* A portion of its orbit brings it closer to the sun than Neptune for approximately 20 years out of each 248. This occurred most recently between February 7, 1979 and February 11, 1999. (I am amazed that they can figure this out down to the very day, for an object so far away....). Fortunately, because of the different "angles" of their orbits from the plane of the Earth's orbit, their orbits do not intersect, so we do not risk a planet / dwarf planet collision at some point in the future that might destroy both celestial objects. [See footnote 2]

* Pluto is approximately 2/3 as big as our moon.

* Pluto has one large moon, Charon, and at least three smaller ones. Some astronomers consider Charon and Pluto to be more like a binary planet system (a "dwarf double planet") rather than planet and moon.


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Footnote 1: Interestingly, in 1992 new data from Voyager 2 indicated that Neptune's mass was sufficient to account for the gravitational effects on Uranus, and that no other planet was needed to account for the disturbances in Uranus' orbit. So, even though the wobbles in Uranus' orbit, combined with the mis-estimation of Neptune's mass, predicted the existence of a planet at a certain place in space, and even though Pluto was discovered to exist there, it was all just a big coincidence.

Footnote 2: When I was in elementary school, we were taught that the planets went, in order, like this: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto. We even built a paper mache model of the solar system and hung the planets from the ceiling in my 2nd grade classroom.

For about 20 years, I guess they had to hang Pluto closer to the sun than Neptune.

And nowadays, I guess there'd be no Pluto hanging from the ceiling. I confess to a certain sense of nostalgic loss.

Although, to argue the other side, I suppose if we did continue to recognize Pluto as a planet, we'd have to learn the names of a whole legion of other similarly sized orbital objects that fall into that "dwarf planet" category that we otherwise get to freely ignore while learning about planets. So I'm guessing elementary school kids all over the world are grateful for Pluto's demotion.