For those with less mythology geekery:
Most of you probably know that Mars was the Roman god of war and Venus the Roman goddess of love.
Saturn (with the rings), known as Cronus in Greek, was the father of the six main gods. Gaea told him he would one day be overthrown by his child, so he swallowed all of his children as soon as they were born. Naturally, his wife was a bit miffed about this, so she gave him a rock instead of Jupiter (aka Zeus, the god of thunder and ruler of the gods). And then Jupiter grew up a kicked his butt, freeing his siblings.
The smaller planet being bullied by Jupiter is Neptune, god of the oceans, who actually was a great god in his own right... but is definitely a much smaller planet, so I guess that's why he looks nervous
Mercury/Hermes is the messenger of the gods, and is known for his staff, winged sandals, and winged helm.
Pluto is the god of death, but since it's no longer considered a planet (boooo!) I guess they locked him up.
So, I guess Uranus is the nerdy one with the glasses... not sure about that one. Uranus was the first lover of Gaea, the Earth. He was the sky. No, really. Next she married the oceans.