All terrestrial planets may have the same basic type of structure; such as a central metallic core, mostly iron, with a surrounding silicate mantle. The Moon is similar, but has a much smaller iron core. Io and Europa are also satellites that have internal structures similar to that of terrestrial planets.
Average ACT: 33. The average ACT score composite at Stanford is a 33. The 25th percentile ACT score is 31, and the 75th percentile ACT score is 34. In other words, a 31 places you below average, while a 34 will move you up to above average. There's no absolute ACT requirement at Stanford, but they really want to see at least a 31 to have a chance at being considered.
The average GPA at Stanford is 4.18. This makes Stanford Extremely Competitive for GPAs. (Most schools use a weighted GPA out of 4.0, though some report an unweighted GPA. With a GPA of 4.18, Stanford requires you to be at the top of your class. You'll need nearly straight A's in all your classes to compete with other applicants. You should also have taken plenty of AP or IB classes to show your ability to excel in academic challenge.