How can we know the size, composition, and atmospheric makeup of distant exoplanets? NASA explains the details in this Alien Atmospheres video.
By observing periodic variations in the parent star’s brightness and color, astronomers can indirectly determine an exoplanet’s distance from its star, its size, and its mass. But to truly understand an exoplanet astronomers must study its atmosphere, and they do so by splitting apart the parent star’s light during a planetary transit.
"Physics told me some crazy stuff. Say, I’m not just sitting here doing nothing. I’m actually fighting against Earth’s gravity. And I’m not sitting still. I’m spinning at a thousand miles per hour, or even more than that… 67 thousand miles per hour, if you count the rotation of the Earth around the Sun…"