give reasons pluto has been downdraded from planet to planetoid.?

Answer 1

International Astronomical Union (IAU) voted this month to redefine a planet. The final voting came from about 400 to 500 of the 2,400 astronomers who were registered at the meeting of the International Astronomical in Prague. There is both a size limit, and a requirement that the object sweep out its orbit. In addition the object must independently orbit the Sun (excluding several large moons of Jupiter). This new classification redefines Pluto as a "dwarf planet", leaving the Solar System with 8 "classical planets". New additions to the dwarf planet class are Sedna, the largest asteroid, Ceres and "Xena" (2003 UB313). Many more objects may join the class, pending more accurate determinations of their size. This definition followed an earlier suggestion that all objects independently orbiting the Sun which have sufficient gravity to become roughly circular should be called planets - such a definition could have dramatically increased the number of planets. Dynamical astronomers argued that the orbital criteria (that the object dominate its orbit) was equally important, thus excluding Pluto, and these many other small objects from the "classical" planets.

According to the new rules a planet meet three criteria: it must orbit the Sun, it must be big enough for gravity to squash it into a round ball, and it must have cleared other things out of the way in its orbital neighborhood. The latter measure knocks out Pluto and Xena, which orbit among the icy wrecks of the Kuiper Belt, and Ceres, which is in the asteroid belt.

This new definition of planets exludes Pluto having been considered a planet for over 3/4 of a century and with a NASA mission (New Horizons) on its way to reach the Pluto-Charon system in July 2015.

According to the new definition, a full-fledged planet is an object that orbits the sun and is large enough to have become round due to the force of its own gravity. In addition, a planet has to dominate the neighborhood around its orbit. The new definition only applies to our own solar system Pluto has been demoted because it does not dominate its neighborhood. Charon, its large "moon," is only about half the size of Pluto, while all the true planets are far larger than their moons.

In addition, bodies that dominate their neighborhoods, "sweep up" asteroids, comets, and other debris, clearing a path along their orbits. By contrast, Pluto's orbit is somewhat untidy. he new definition also establishes a third class of objects that orbit the sun—"solar system bodies," which would apply to many asteroids, comets, and moons.

The new definition of "planet" retains the sense that a true planet is something special. It has long been clear that Pluto, discovered in 1930, stood apart from the previously discovered planets. Not only was it much smaller than them, only about 1,600 miles in diameter, smaller than the Moon, but its elongated orbit is tilted with respect to the other planets and it goes inside the orbit of Neptune part of its 248-year journey around the Sun.

Pluto makes a better match with the other ice balls that have since been discovered in the dark realms beyond Neptune, they have argued. In 2000, when the new Rose Center for Earth and Space opened at the American Museum of Natural History, Pluto was denoted in a display as a Kuiper Belt Object and not a planet.

Answer 2

The reason is that Pluto never was a planet and astronomers have finally corrected their mistake. To be sure, when Pluto was discovered in 1930 not much could be determined about its make up. As more became known about Pluto it became clear it just didn't fit in with the other two sets of planets: it was not a small, rocky planet like the four inner planets, nor was it a large, gaseous planet like the four outer planets. It; along with its "moon", Charon; were small chunks of ice, much like a lot of the space junk orbiting on the fringes of the solar system.

Answer 3

Because they discovered dozens of Pluto like object, which means if we continue to make Pluto a planet we should also consider all the Pluto like object as planets which can cause dozens of additional planets.

Answer 4

I guess it finally became worthy of my notice.