Definitions by Andrew scrivner

perihelion 

The point during its orbit when a celestial body is closest to its star

When earth is closest to the sun in its eliptical orbit

perihelion by Andrew scrivner April 28, 2005

gas giant planets

Either of the gas giants including Neptune, Uranus, Saturn, and Jupiter These planets have no solid surface but have a solid core, and are mostly composed of gasses

Neptune, Uranus, Saturn, and Jupiter are the 4 Gas Giant Planets

gas giant planets by Andrew scrivner April 28, 2005

Planetesimal 

Planetesimals are objects of some Km of diameters that are thought to have formed during the solar system's formation.

Asteroids and comets are leftover planetesimals that have not been incorporated into a planet during this period

Planetesimal by Andrew scrivner April 28, 2005