Estimate
A simulated terrestrial planet forms a massive moon
- Probability:
- 8.33%
- Odds:
- 1 to 11
- dBan
- −10.4 dBan
In Elser and colleagues’ simulated impacts, an Earth–Moon-like outcome appeared for about one in 12 terrestrial planets.
Calculation
p ≈ 15 / 180 ≈ 1/12 ≈ 0.083; sensitivity range ≈ 1/45 to 1/4
Assumptions
The 2011 study’s nominal estimate counts 15 matches among about 180 simulated planets, with host mass above 0.5 Earth masses and moon mass above 0.5 lunar masses. The 1/45-to-1/4 range comes from sensitivity choices, not a confidence interval or a measured galactic frequency. Initial conditions and the small simulated sample add uncertainty; extreme satellite-accretion efficiencies widen the outcomes from almost no systems to about 60 systems among 180, roughly one-third.
Sources
- Elser et al. (2011): how common are Earth–Moon planetary systems? simulation study and sensitivity range checked 27 October 2026