Mars had an oxygen-rich atmosphere around 4 billion years ago
13
All of the Earth's continents are wider at the north than in the south - and nobody knows why.
194
Jupiter is bigger than all the other planets combined.
254
The Earth gets heavier each day by tons, as meteoric dust settles on it.
118
A 100-pound person on Earth would weigh 38 pounds on Mars.
102
A comet's tail always points away from the sun.
2