Through theoretical modeling, Aurélien Crida of the University of Nice Sophia - Antipolis and Sébastien Charnoz of the University of Paris Diderot found that the moon - formation action begins at the edge of a planetary ring, where a satellite can take shape without being shredded by the gravitational pull of the planet. (scientificamerican.com)
Previously, astronomers relied on follow - up radial velocity observations, which look for the degree to which the gravitational pull of the planet perturbs the star that it orbits, to determine the masses of such planets. (sciencemag.org)
The original claim was based on the radial velocity method — a planet - hunting technique which looks at how the gravitational pull of a planet slightly wobbles its star. (newscientist.com)