Small Fish, Big Pond

XKCD has a cool infographic showing what it takes to escape the gravity well of the major bodies of the solar system.

Astronomy has been a passing interest of mine since childhood, so it’s always cool to see a simplified version of the dynamics of gravity so it’s a bit easier to wrap your head around.

I like the description of Deimos and Phobos, if man ever makes it out there I think being the first person to throw a baseball into Phobos’ orbit is just as cool as being the first person to land on the moon or a planet.

The Earth has a huge moon for its size and is pretty unique in that regard. All other minor planets have little more than rocks orbiting them. The only other heavenly body with a closer ratio of planet to moon is Pluto which technically isn’t a planet anymore.

Pluto and Charon are so closely matched in size that the center of gravity between them is above the surface of Pluto. Imagine linking hands with somebody twice your weight and then the two of you spinning around. Your hefty friend will orbit the center of gravity in a smaller loop than you will.

Jupiter is sometimes referred to as the “Star that almost was.” Its gravity isn’t quite enough to compress hydrogen enough to begin the process of fusion. Gas Giants between the size of Jupiter and actual stars are referred to as “Brown Dwarfs”, referring to the fact that they don’t have high enough gravity to sustain fusion. If additional mass falls into them they can “ignite” and become stars; this was used as a plot device in 2010: Odyssey Two, where the Monoliths reproduce in Jupiter lowering the density and causing the planet to ignite into a second sun.