What is the lightest known exoplanet?
The lightest known exoplanet is PSR B1257+12 b, at 0.02 times the mass of Earth: heavier than our Moon and lighter than Mercury. Everything about PSR B1257+12 b →
| # | World | Mass | Distance |
|---|---|---|---|
| ★ 1 | PSR B1257+12 b | 0.02× Earth's mass | 1,957 ly |
| 2 | Kepler-879 c | about 0.036× Earth's mass | 2,618 ly |
| 3 | Kepler-444 b | about 0.037× Earth's mass | 119 ly |
| 4 | Kepler-158 d | about 0.047× Earth's mass | 1,028 ly |
| 5 | Kepler-80 g | 0.065× Earth's mass | 1,205 ly |
| 6 | Kepler-138 b | 0.07× Earth's mass | 218 ly |
| 7 | Kepler-444 c | about 0.079× Earth's mass | 119 ly |
| 8 | Kepler-1489 c | about 0.087× Earth's mass | 4,185 ly |
| 9 | Kepler-1994 b | about 0.087× Earth's mass | 789 ly |
| 10 | Kepler-1308 b | about 0.093× Earth's mass | 368 ly |
| 11 | Kepler-444 e | 0.100× Earth's mass | 119 ly |
| 12 | GJ 238 b | about 0.126× Earth's mass | 49.6 ly |
| 13 | Kepler-1583 b | about 0.156× Earth's mass | 1,317 ly |
| 14 | Kepler-1998 b | about 0.156× Earth's mass | 1,112 ly |
| 15 | Kepler-963 c | about 0.156× Earth's mass | 2,516 ly |
| 16 | Kepler-1087 b | about 0.165× Earth's mass | 1,183 ly |
| 17 | K2-89 b | about 0.170× Earth's mass | 281 ly |
| 18 | Kepler-1877 b | about 0.179× Earth's mass | 931 ly |
| 19 | Barnard e | at least 0.193× Earth's mass | 6.0 ly |
| 20 | Kepler-1371 c | about 0.196× Earth's mass | 1,681 ly |
| 21 | Kepler-444 d | 0.200× Earth's mass | 119 ly |
| 22 | Kepler-1130 d | about 0.202× Earth's mass | 813 ly |
| 23 | Kepler-1351 b | about 0.208× Earth's mass | 661 ly |
| 24 | Kepler-1542 c | about 0.208× Earth's mass | 1,302 ly |
| 25 | Kepler-271 d | about 0.219× Earth's mass | 1,319 ly |
Showing the top 25 of 6,285 that qualify.
Small masses are the hardest measurement in the catalog, because a light planet tugs its star only faintly. The worlds at the top of this table are measured in two very different ways: a few come from pulsar timing, where the clockwork beat of a dead star reveals a nudge of a hundredth of an Earth mass, and the rest are estimated from a measured radius using the relationship between a planet's size and its likely mass.
Where a mass is estimated from radius rather than measured, this site says so on the planet's own page and phrases it as an estimate. Disputed rows and our own solar system's moons and dwarf planets are excluded: Charon is lighter than anything here, but it is a moon of Pluto, not an exoplanet.
What is the lightest known exoplanet?
The lightest known exoplanet is PSR B1257+12 b, at 0.02 times the mass of Earth: heavier than our Moon and lighter than Mercury.
How can astronomers weigh a planet that light?
Two ways. A pulsar is a dead star that flashes with the regularity of an atomic clock, so a planet's gravitational tug shows up as a few microseconds of delay in the beat, which is enough to weigh a world a fiftieth of Earth's mass. Everywhere else, the mass is inferred from a measured radius, because rock and iron of a known size can only weigh so much.
How does the lightest exoplanet compare with our Moon?
PSR B1257+12 b is heavier than our Moon and lighter than Mercury, where our Moon is 0.012 Earth masses and Mercury is 0.055. Our own solar system holds far lighter bodies than any of them, but they are moons, asteroids and dwarf planets rather than planets around another star.
Why are there no lighter planets in the catalog?
Because we cannot see them yet, not because they are not there. Every detection method is biased toward big planets: a lighter world makes a smaller wobble and a shallower transit, so the low-mass end of this table is a map of what our instruments can reach rather than of what exists.
Keep exploring: all records · the smallest planet by size · how planet masses are measured