Mercury

Some basic facts:

• radius ~ 0.4 R_Earth
• distance from sun ~ 0.4 AU, but quite eccentric
  • min distance = 0.31 AU
  • max distance = 0.47 AU
• hot, with big variation
  • nighttime temp ~ 100 K
  • daytime temp ~ 600 K

Density:

• Density is 5400 kg/m³.
• This is similar to Earth's density.
• So need an iron core.
• Furthermore, since Mercury is smaller, it is not as compressed by its own gravity.
• So its core needs to be a bigger fraction of the planet than for the Earth.

  Essentially no atmosphere.

  Lots of craters.