Expert: Ed - 2/19/2004

Question
What are terrestial planets? What are jovian planets? what aret the main differences between the two?  Which ones have a primarly gaseous compostition and which ones havea rocky composition? What planet is the smallest and which one is the biggest? Which one is closest to the sun? Personly if I was thinking earth and I always thought earth was the smallest and that jupitor is was the biggest. If I am wight on this then disreguard the quesitons about size.

                                         Thanks,
                                             Joe

Answer
Joe,

Terrestrial planets are relatively small, and rocky, like Mercury, Venus, Earth, and Mars.  Jovian planets are gigantic and gaseous, like Jupiter, Saturn, Uranus, and Neptune.  Pluto is more like the terrestrial planets than the Jovian planets, because it's little and rocky, but astronomers don't usually include it among the terrestrial planets.  This is because it's waaaaayyyyyyyyyyy out at the edge of the solar system, and we're used to calling those planets "Jovian."

This website answers your other questions:
http://seds.lpl.arizona.edu/nineplanets/nineplanets/datamax.html

Jupiter is the largest planet of all.  Pluto is the smallest planet.  Mercury is closest to the sun.

Earth is much, much, much smaller than Jupiter, so you're exactly right about that!  However, Earth is actually the LARGEST of the TERRESTRIAL planets.  That gives you some idea of how much huger the jovian planets are, than the terrestrial planets.

I hope this is helpful.  Keep Looking Up!
-Ed