The Universe is filled with planets. Astronomers have so far confirmed more than 4,500 worlds, with more than 1,500 of these being rocky terrestrial planets. Within our Solar System, the rocky planets — Mercury, Venus, Earth, and Mars — are quite different from each other. But once you begin to look at systems around other stars, the diversity we see in our Solar System is left in the dust. These distant worlds can be amazingly bizarre, unlike anything we have imagined. Some are super-earths, some rain rocks. Some have winds that rage at thousands of kilometers an hour, and others are made of diamond.
But how do astronomers know what these worlds are like? Basking in the glow of their parent star, these planets are nearly invisible. Scientists can only determine these planets exist by looking at their parent star; maybe it wobbles a bit under the planet’s gravitational pull, or maybe the light dims as the planet passes in front of it. But seeing these planets directly? Unlikely. Yet, astronomers have a few tricks up their sleeve that allow them to deduce the properties of these alien worlds.
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