What is the smallest known exoplanet?
The smallest known exoplanet is Kepler-37 b, about 0.31 times the radius of Earth: between our Moon and Mercury in size. Everything about Kepler-37 b →
| # | World | Radius | Distance |
|---|---|---|---|
| ★ 1 | Kepler-37 b | 0.31× Earth's radius | 208 ly |
| 2 | PSR B1257+12 b | 0.34× Earth's radius | 1,957 ly |
| 3 | Kepler-37 e | 0.37× Earth's radius | 208 ly |
| 4 | Kepler-879 c | 0.40× Earth's radius | 2,618 ly |
| 5 | Kepler-444 b | 0.40× Earth's radius | 119 ly |
| 6 | Kepler-158 d | 0.43× Earth's radius | 1,028 ly |
| 7 | Kepler-102 b | 0.46× Earth's radius | 352 ly |
| 8 | Kepler-444 c | 0.50× Earth's radius | 119 ly |
| 9 | Kepler-1994 b | 0.51× Earth's radius | 789 ly |
| 10 | KOI-4777.01 | 0.51× Earth's radius | 562 ly |
| 11 | Kepler-1489 c | 0.51× Earth's radius | 4,185 ly |
| 12 | Kepler-1308 b | 0.52× Earth's radius | 368 ly |
| 13 | Kepler-444 d | 0.53× Earth's radius | 119 ly |
| 14 | Kepler-62 c | 0.54× Earth's radius | 981 ly |
| 15 | Kepler-444 e | 0.55× Earth's radius | 119 ly |
| 16 | GJ 238 b | 0.57× Earth's radius | 49.6 ly |
| 17 | Kepler-102 c | 0.57× Earth's radius | 352 ly |
| 18 | Kepler-42 d | 0.57× Earth's radius | 131 ly |
| 19 | Kepler-1583 b | 0.60× Earth's radius | 1,317 ly |
| 20 | Kepler-963 c | 0.60× Earth's radius | 2,516 ly |
| 21 | Kepler-1998 b | 0.60× Earth's radius | 1,112 ly |
| 22 | KOI-1843.03 | 0.61× Earth's radius | 438 ly |
| 23 | Kepler-1087 b | 0.61× Earth's radius | 1,183 ly |
| 24 | K2-89 b | 0.61× Earth's radius | 281 ly |
| 25 | Kepler-1877 b | 0.62× Earth's radius | 931 ly |
Showing the top 25 of 6,267 that qualify.
A transiting planet's size comes straight from geometry: the fraction of starlight it blocks. That makes the small end of the radius table one of the most trustworthy rankings on the site. Disputed rows are excluded, and so are the small bodies of our own solar system: Charon, Pluto, and our Moon are all smaller than any confirmed exoplanet, but they are not exoplanets.
What could unseat this record: space telescopes can now catch the dip from a body smaller than our Moon crossing a quiet star, so this is one of the most beatable records on the books.
What is the smallest known exoplanet?
The smallest known exoplanet is Kepler-37 b, about 0.31 times the radius of Earth: between our Moon and Mercury in size.
How small is the smallest known exoplanet?
Kepler-37 b measures 0.31× Earth's radius, which puts it between our Moon and Mercury in size. It is smaller than any planet in our own solar system.
How can astronomers measure something that small?
By the shadow it casts. When a planet crosses its star, it blocks a fixed fraction of the light, and that fraction is a direct ratio of the two sizes. For the smallest worlds the dip is a few parts per million, which is why they were found by space telescopes above the atmosphere's noise.
Is there a smallest possible planet?
There is no hard floor, only a definitional one: an object has to be massive enough for gravity to pull it round, which happens somewhere around a few hundred kilometres across for rock. Below that you have an asteroid, and no survey could detect one around another star anyway.
Keep exploring: all records · all rocky worlds