Nine Planets Of Solar System

Frederick Said:

what are the two main general categories (excluding Pluto) into which the nine planets of our solar system..?

We Answered:

Terrestrial planets (Mercury, Venus, Earth, and Mars), also called inner planets.
Jovian planets (Jupiter, Saturn, Uranus, and Neptune) also called gas giants or outer planets.

Nora Said:

please give me a complete data sheet for each of the nine planets of the solar system.?

We Answered:

http://www.nasa.gov/worldbook/index.html

Tamara Said:

Why are their only nine planets in the solar system?

We Answered:

There are actually only eight planets in the solar system (Pluto is no longer a planet). The eight planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Simply put, the definition of a planet (as decided by the International Astronomical Union) is
1. It has to orbit the sun
2. It has to be round
3. It has to have cleared out its space

There are only eight objects in our solar system that fit all of these classifications

Pluto is in the Kuiper belt. The Kuiper belt is sort of like the asteroid belt. Because there are many other objects in the Kuiper belt and the asteroid belt, objects within them have obviously not "cleared out their space". Objects include Ceres (in the asteroid belt), Pluto, and Eris (a Kuiper belt object which is larger than Pluto). These objects are classified as "dwarf planets".

Jennifer Said:

On which of the nine planets in the Solar System would you weigh the least?

We Answered:

pluto at 6.5 pounds (165 here)

Eugene Said:

why did the scientists remove pluto from the list of the nine planets in our solar system?

We Answered:

The definition of a planet was changed in 2006 by the International Astronomical Union (IAU).

A planet is now defined as a celestial body that:

- is in orbit around the Sun,
- has sufficient mass so that it assumes a hydrostatic equilibrium (nearly round) shape, and
- has "cleared the neighborhood" around its orbit.

Since Pluto has neither a hydrostatic orbit (it's elliptical) and it hasn't cleared it's orbit (it crosses Neptune's orbit) the it was de-classified as a planet.

It is for these reasons too that the 'new' planets discovered beyound Pluto are not designated as planets.

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