Mercury is a prime example of a crater planet
Crater planet is a class of planet with surface pockmarked with impact craters, just like the surface of the Moon.
Characteristics[]
Crater planets tend to have brief periods of geologic activities and usually have little or no atmospheres, otherwise it would have eroded away much of the craters. Also, crater planets are usually small, about half the size of Earth and one-tenth the mass. Small, low-mass planets are not as active as their more massive cousins. Their lack of geologic activities mean that there are little or no volcanic and tectonic activities. Small, low-mass planets also have little gravity, so they don't hold on the gases well, allowing the stellar winds to strip away the atmospheres easily.
Habitability[]
The life-bearing status of crater planets are poor, although present-day microbial life could likely exist in the rocks and underground on Mars. Life may thrive underground in caves or in aquifers. Thriving underground is advantageous because the ground above can shield life from radiation and meteor impacts.
Abundance[]
There are an estimated 169 billion crater planets in our galaxy alone, making it the second most abundant surface class of rocky planet after barren planet. This corresponds that 323‰ of all 524 billion terrestrial planets and 206‰ of all 820 billion planets in our galaxy are crater planets. It is one of five out of eight surface classes of planets with abundances of at least 100 billion.
Speculated crater planets[]
There are two crater planets in our solar system — Mercury and Mars. Both planets have little to no atmospheres and are geologically dead. Mercury's surface is more heavily cratered than Mars. As of February 2014, there are only five probable crater exoplanets out of over a thousand — Kepler-42d (Idunn), KIC 12557548 b (Iberia), Kepler-37b (Cobis), Kepler-62c (Esus), and Kepler-102c (Dian Cecht).
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