BOSTON—The number of Earth-like extrasolar planets suitable for harboring advanced life could be 10 times higher than has been assumed until now, according to a new modeling study. The finding contradicts the prevailing notion that a terrestrial planet needs a large moon to stabilize the orientation of its axis and, hence, its climate. In 1993, French mathematicians Jacques Laskar and Philippe Robutel showed that Earth’s large moon has a stabilizing effect on our planet’s climate. Without the moon, gravitational perturbations from other planets, notably nearby Venus and massive Jupiter, would greatly disturb Earth’s axial tilt, with vast consequences for the...