Astronomy

Professor Kimber walks anxiously into the classroom where she finds an excited group of students chattering. She clears her throat, clearly nervous and addresses the class, "Welcome to your first astronomy lesson, I am your professor, Kimber and I am very happy to teach you and hope you are happy to be in my class."
She was pleased to note most of the class was attentive.
'This lesson is on Terrestial and Jovian plantes, I know its a tad boring but it will get better, I promise.' she says. 'The four inner planets, Mercury, Venus, Mars and Earth are all terrestial planets. This is because they are small, dense rocky worlds with little or no atmosphere. The Outer four planets, Jupiter, Saturn, Uranus and Neptune are all Jovian planets because they are large, low density worlds with thick atmopsheres and large interiors. Pluto belongs in neither of these classes because it is small and low density. Earth is the largest Terrestial planet, but the Jovians are much larger. For example, Jupiter is over 300 earth masses."
Professor Kimber suddenly turned round and realised she was out of time.
"That will be all today," she told her students. "Your homework is posted and points will be given accordingly."

Homework:
1) Why are Mercury, Venus, Mars and Earth all terrestial?
2) Which planets are Jovian? Why?
3) Which planet is not found in either category?
4) How much larger is Jupiter than Earth?

Email Professor Kimber your homework at Kimber68714@aol.com