From Ron Baker
Your story on planetary rings and moon formation (8 December, p 18) is interesting, but Earth’s moon seems too massive to have originated from a ring system. However, the possibility that early Earth had such a system supports the capture hypothesis for the origin of the moon.
The moon could have been captured by Earth through gravitational interaction or collision with a moonlet already formed from the rings, or with ring material itself.
Colchester, Essex, UK
