A hidden planet reveals itself by yanking on its neighbor

In 1990, not a single planet outside our solar system was known. Now, not only do we know of thousands, but we have also have an almost embarrassing number of ways to find them.

You may have heard of the transit method, where a planet passes in front of its star, and we see a dip in the amount of starlight, like a mini-eclipse. This is the most successful method so far, and gives us the radius of the planet. You may also know the radial (or reflex) velocity method, where a planet tugs on its st...