How common are Earth-Moon planetary systems?

TL;DR

This study investigates the frequency of Earth-like planets with massive moons, finding that such systems are relatively common, occurring in at least 1 in 45 to 1 in 4 cases, based on simulation data and impact analysis.

Contribution

It provides the first quantitative estimate of how common Earth-Moon-like systems are among terrestrial planets using collision simulations and impact criteria.

Findings

Massive moons are not rare around terrestrial planets.

Giant impact conditions for moon formation occur in over 1 in 12 cases.

Estimated occurrence rate ranges from 1 in 45 to 1 in 4 planets.

Abstract

The Earth's comparatively massive moon, formed via a giant impact on the proto-Earth, has played an important role in the development of life on our planet, both in the history and strength of the ocean tides and in stabilizing the chaotic spin of our planet. Here we show that massive moons orbiting terrestrial planets are not rare. A large set of simulations by Morishima et al., 2010, where Earth-like planets in the habitable zone form, provides the raw simulation data for our study. We use limits on the collision parameters that may guarantee the formation of a circumplanetary disk after a protoplanet collision that could form a satellite and study the collision history and the long term evolution of the satellites qualitatively. In addition, we estimate and quantify the uncertainties in each step of our study. We find that giant impacts with the required energy and orbital parameters for producing a binary planetary system do occur with more than 1 in 12 terrestrial planets hosting a massive moon, with a low-end estimate of 1 in 45 and a high-end estimate of 1 in 4.