The Moon is 25% of the Earth's diameter. Its density is 3.4 gm/cm3 implying a mostly rocky core (vs. metallic core for the Earth). It does not have any atmosphere. Impact craters: The Moon's surface is heavily cratered. There are Mares (Basins).
Mercury is a heavily cratered planet closest to the Sun. In some ways, it most resembles the Moon. The density of Mercury is 5.4 gm/cm3 . Impact craters Scarps Hot/Cold, no atmosphere
In mass and density, Venus is nearly the Earth's twin. Venus' atmosphere is very thick and opaque. The atmosphere is about 95% carbon dioxide (CO2 ). Other components are also present: N, water vapor, sulfuric acid. Heat is trapped near the planet's surface by a runaway Greenhouse Effect that produces a surface temperature of nearly 470o C. The planet has been imaged from orbit using the Magellan radar mapping system. The surface was photographed by the Russian Venera spacecraft. There are Volcanos, Coronae, archnoids, ``pancakes'', impact craters (more than on the Earth, but less than on the Moon).
The Atmosphere is 79% nitrogen, 20% oxygen, and 1% other trace gases. The Earth's surface is active, constantly destroyed and renewed in large sections. This is called plate tectonics. Plate tectonics: slow motion of large pieces of crust. There is water and there are oceans. There is LIFE !!!
Mars has a mass of about 10% that of Earth. Its density is 3.9gm/cm3 . The peak surface temperature is nearly 20o C (but minimum is -140o C). Mars also has polar ice caps (water ice! and frozen CO2 ). The atmosphere is 95% CO2 , but much thinner than that for Venus or Earth. There are Volcanos (Olympus Mons), Canyons (Valles Marineris). Therer are traces of erosion: dry riverbeds. There winds and dust storms. Polar caps: Underground water ??