By most measures, Earth is small. The solar system's largest planet, Jupiter, could fit over 1,300 Earths inside it. But Earth isn't the smallest planet in the solar system; that title went to Mercury after Pluto was relegated to a dwarf planet in 2006. But are there even smaller planets out there? And, if so, do we know of any?
Unsurprisingly, very small exoplanets, or planets orbiting other stars, are extremely hard to spot. But of the ones scientists have found, the smallest is Kepler 37-b. Discovered in 2013 by scientists using data from the Kepler space telescope, it is smaller than Mercury and about the same size as Earth's moon.
