Scientists may soon find out.
Orbiting objects exert a gravitational pull on each other. This gravitational pull is what gives objects their weights; it’s the reason that you weigh 83% less on Earth’s moon than on Earth, without losing any of your mass.
Scientists are currently using measurements of objects’ gravitational pulls to find new planets around stars. As a planet orbits around a star, it pulls on the star, making the star appear to wobble. Looking for the wobble (as you can do in our space investigation”Is there life outside of Earth?“) is how scientists find objects around stars.
David Kipping, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, realized that by using the same strategy with a planet and its orbiting moon, along with some calculation using Kepler’s Laws of Motion, scientists will be able to determine the mass of distant stars.
In essence, they’re just measuring the wobble effect that all three objects (star, planet, and moon) exert on each other. All they need to do now is find stars that have planets that have at least one moon.
“When they’re found, we’ll be ready to weigh them,” said Kipping.