Weighing a planet is a tough task. I mean, it's not like you can just put them on a bathroom scale. And, while astronomers figured out how to measure the mass of planets in our solar system a long time ago, it's practically impossible to weigh exoplanets. Well, it was until recently.
MIT planetary scientists Julien de Wit and Sara Seager just devised a method that enables them to weigh an exoplanet by measuring the starlight that shines through its atmosphere. It's so simple, it's genius. See, when an exoplanet passes in front of its star, it causes a blip in the amount of light that shines toward Earth. This is actually how we're able to discover exoplanets in the first place.