Wednesday, August 16

Planets in our Solar System

What are the planets in our Solar System?
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.
(You can remember these 9 plantes by:
My Very Educated Mother Just Showed Us Nine Planets)

Wrong answer! The International Astronomical Union found that the definition of "planet" was ambiguous, after a new asteroid was found bigger than Pluto. So, she proposed to make the definition as:
Planet is an celestial body which is heavy enough so that the self-gravity make the shape ball-like, and it should be in an orbit of a star.

By this definition, we have 12 planets now:
Ceres was found in 1801, and at that time it was announced as a planet, but be reclassified as asteroid (small celestial body) soon later. It locates in an orbit between Mars' and Jupiter's, and it's diameter is one-fourth of the Moon's, and one-third of the Pluto's.
Pluto has a brother asteroid. That is not a satellite of Pluto, because these two asteroids go around each other, like a "double star". So, we should call them "Plutos", and both of them are planets, by the new definition.
Xena, which as found in 2003 and created this discussion, is a little bit bigger than Pluto.

There are other asteroids which are not confirmed about their shape yet, but scientists warned IAU that more planets will be found, following this new definition.

Temporary, our solar system is like:
new planets
(picture from MSNBC)