Sub-Earth

Sub-Earth exoplanets are among the most difficult type to detect because their small sizes and masses produce the weakest signals.

The smallest known is WD 1145+017 b with a size of 0.15 Earth radii, or somewhat smaller than Pluto.

[2] It is orbiting within a thick cloud of dust and gas as chunks of itself continually break off to then spiral in towards the star, and within around 5,000 years it will have more-or-less disintegrated.

[1][4] There is suspected to be a sub-Earth orbiting Proxima Centauri, the closest star to the Sun.

[1] Due to their small sizes, and unless there are significant tidal forces when orbiting close to the parent star, sub-Earths also have short periods of geologic activity.