Pluto's Consolation Prize

I remember when I was in the 2nd grade, we each sit in a chair attached to a small desk. The desk had a photo of the sun and the nine planets that orbit it. This is possibly the first time rote memory was introduced to me. Looking at that glossy, transparent plastic covered photo everyday for 1 year, I could still see the vivid colors of crimson red, blue, yellow, black, blue, green & brown, the sun in the center with the 9 planets forming a circle.

I remember how I memorized the placement of the planets nearest to the sun.

m-v-e-m-j-sunp --------------9 planets orbiting the sun. NINE!

40 years later, it is determined that there are only 8. Pluto got sacked!

Once known as the smallest, coldest, and most distant planet from the Sun, Pluto has a dual identity, not to mention being enshrouded in controversy since its discovery in 1930. Pluto is also a member of a group of objects that orbit in a disc-like zone beyond the orbit of Neptune called the Kuiper Belt. This distant region consists of thousands of miniature icy worlds with diameters of at least 1,000 km and is also believed to be the source of some comets.

Pluto has three known moons, Hydra and Nix, besides its companion moon, Charon. Charon's diameter is a little more than half of Pluto's. The duo's gravity has locked them into a mutually synchronous orbit, which keeps each one facing the other with the same side. Many moons - including our own - keep the same hemisphere facing their planet. But this is the only case in which the planet always presents the same hemisphere to its moon. If you stood on one and watched the other, it would appear to hover in place, never moving across the sky.
Charon was discovered in 1978, while two additional moons Hydra and Nix, were discovered in 2005.

In Greek mythology, Charon was the boatman who carried the souls of the dead to the underworld - a kingdom that in Roman mythology was ruled by the god, Pluto. The U.S. Naval Observatory's James Christy suggested the name after he found the moon in 1978. Seven years later, Charon and Pluto began a five-year period of eclipsing each other from Earth's point of view. That was lucky for us, because it enabled scientists to measure the diameters and masses of both objects as each passed in front of the other.

Charon appears to be covered by water ice, which differs from Pluto's surface of frozen nitrogen, methane, and carbon dioxide. One theory is that the materials that formed Charon were blasted out of Pluto in a collision. That's very similar to the way in which our own moon is thought to have been created.

The ninth rock from the sun is now officially a plutoid. The official definition of Plutoid is: Any celestial bodies in orbit around the sun at a distance greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighborhood around their orbit."

In short: small round things beyond Neptune that orbit the sun and have lots of rocky neighbors.
The two known and named plutoids are Pluto and Eris. Remember how Pluto was stripped off its planetary status about 2 years ago?

"Pluto has been given a consolation price. All so called dwarf planets and similar distant bodies in the solar system will be called "plutoids." That's the decision by the International Astronomical Union, which met last week in Oslo, Norway, and announced the decision Wednesday. The new policy allows Pluto to be the standard for a whole new category of dwarf planets.

Pluto is one of only two plutoids, the other being Eris. Both are objects that circle the sun and are too small to be considered planets, but big enough to have a level of gravity that keeps them in a near spherical shape. Plutoids also must be farther from the sun than Neptune.

A growing number of solar-system scientists assert that Pluto's minuteness and its membership in a swarm of like objects mean that it should be classified a "minor planet," as asteroids and comets are. Others are outraged by the idea, insisting that regardless of how its identity has changed, demoting Pluto would dishonor astronomical history and confuse the public.

"Pluto has been a long-standing myth that's difficult to kill," he says.

The famous "search for Planet X," which culminated in Pluto's discovery, was the pet project of Percival Lowell, a Boston Brahmin and amateur astronomer who around the turn of the century became obsessed with two notions: that Martians had constructed canals on the surface of their planet, and that tiny, gravity-induced wiggles in the orbits of Uranus and Neptune indicated that a planet with a mass some six times that of Earth lay farther out. Lowell built and endowed an impressive observatory in Flagstaff, Arizona, to prove himself right, but he died in 1916 without having succeeded on either count. The observatory's directors, aware that their institution was something of a laughingstock because of the Martian search, were determined to salvage its reputation by finding at least a marginally less improbable Planet X. They hired a young amateur astronomer by the name of Clyde Tombaugh to do the grunt work involved. Tombaugh proved to be resourceful and diligent beyond all reasonable expectations, and more or less single-handedly picked dim Pluto out of a thick field of stars—a feat that is still considered one of the most impressive in the history of observational astronomy.

In the ensuing euphoria over the apparent discovery of a new planet (elation was especially pronounced in the United States, where the public was happy to welcome the first "American" planet to the solar system), those voices that questioned Pluto's size were drowned out, and the IAU awarded Pluto official planet status. It wasn't an entirely unreasoned decision. As the observatory argued, Pluto had been found close to where Lowell had predicted Planet X ought to be if it was causing those orbital wiggles (though Tombaugh, skeptical of Lowell's predictions, hadn't focused his search on that area), so it would be quite a coincidence if this new object wasn't the enormous Planet X. Besides, if the object was small, it shouldn't have been visible at all so far away from Earth.

Unless, that is, this new object happened to have a highly reflective icy surface, like that of a comet—which eventually proved to be the case. Pluto is much too small to account for the wiggles on which Lowell had based his predictions. Not that that matters, for there were no wiggles—the observations that had implied them were erroneous. And even if there had been wiggles, they probably wouldn't have led astronomers to Planet X, because Lowell's calculations were dubious at best. It was sheer coincidence that Pluto happened to be at the predicted spot. And so it was on a staircase of mistakes, hubris, and hype that Pluto was elevated to planethood.

Later on, scientists have discovered sixty objects in what has come to be known as the Kuiper Belt, named after the astronomer Gerard Kuiper, who suggested the existence of such a belt in the 1950s. About a third of them are in Pluto-like orbits, and all of them appear to be, like Pluto, amalgams of ice and rock. As a result, few astronomers now question that Pluto should be regarded as a member of the Kuiper Belt. However, Pluto's diameter of approximately 1,400 miles makes it tiny for a planet, it is huge for a Kuiper Belt object; the next largest known member is only about 300 miles across.

When the small, rocky body later named Ceres was discovered between the orbits of Mars and Jupiter, in 1801, it was proclaimed a planet. A year later a second rocky body was found in a similar orbit; several other discoveries along the same lines soon followed. Even though the approximately 600-mile-wide Ceres is nearly twice the size of the next largest asteroid, it was evident that it was merely the largest member of what we now call the asteroid belt. In 1802 Ceres's planethood was summarily revoked. Ergo, Pluto should follow Ceres's trail into nonplanethood. It would help if "planet" had a formal definition against which Pluto could be measured, but none exists. Astronomy got by quite nicely for thousands of years on a we-know-one-when-we-see-one basis. But now that questions about Pluto are forcing the issue, many astronomers find themselves gravitating toward one or the other of two proposed definitions.

The first is "a non-moon, sun-orbiting body large enough to have gravitationally 'swept out' almost everything else near its orbit." Among the nine planets Pluto alone fails this test, and it does so spectacularly, owing to the Kuiper Belt. The second is "a non-moon, sun-orbiting body large enough to have gravitationally pulled itself into a roughly spherical shape." Pluto passes this test—but so do Ceres, a half dozen or so other asteroids, and possibly some other members of the Kuiper Belt.

"The International Astronomical Union has decided that Pluto and Eris should be classified as "plutoids," alongside their 2006 classification as dwarf planets. Under the definition, the self-gravity of a plutoid is enough for it to achieve a near-spherical shape, but not enough for it to clear its orbit of its rocky neighbors, and the plutoid orbits the Sun beyond Neptune."

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Imagine the imensity of the universe.....


One way to help visualize the relative sizes in the solar system is to imagine you're doing a model in which everything is reduced in size by a billion. Then model Earth would be about the size of a grape. The Moon would be about 12 inches or about a foot from the Earth. The Sun's size would be about the height of a man and its distance from the Earth is about a city block. Jupiter would be the size of a large grapefruit and 5 blocks away from the Sun. Saturn will be the size of an apple would be 10 blocks away; Uranus and Neptune would be the size of lemons 20 and 30 blocks away. A human on this scale would be the size of an atom and the nearest star would be over 40,000 km away.

I don't know how our puny minds can even begin to comprehend that enormity, that vastness.