New technique measures mass of exoplanets

Method will help scientists determine the mass of exoplanets that are not measurable in any other way. To date, scientists have confirmed the existence of more than 900 exoplanets circulating outside our solar system. To determine if any of these far-off worlds are habitable requires knowing an exoplanet's mass - which can help tell scientists whether the planet is made of gas or rock and other life-supporting materials. But current techniques for estimating exoplanetary mass are limited. Radial velocity is the main method scientists use: tiny wobbles in a star's orbit as it is tugged around by the planet's gravitational force, from which scientists can derive the planet-to-star mass ratio. For very large, Neptune-sized planets, or smaller Earth-sized planets orbiting very close to bright stars, radial velocity works relatively well. But the technique is less successful with smaller planets that orbit much farther from their stars, as Earth does.