What would it take to hide an entire planet? It sounds more like a question posed in an episode of Star Trek than in academic discourse, but sometimes the bleeding edge of science blurs with themes found in science fiction.

Of course we’ve been leaking our own position to distant stars via radio and television signals for six decades now, largely ignorant of the cosmic implications. But several notable scientists, such as Stephen Hawking, have publicly voiced concerns about revealing our presence to other civilizations. These concerns largely draw from the darker chapters of our own history, when a more advanced civilization would subjugate and displace a less advanced one.

It might be too late for us to withdraw back into invisibility, but maybe not for other intelligent alien civilizations out there. A far-off planet’s inhabitants might prefer to hide from the likes of us. Recently, my graduate student Alex Teachey and I published a paper that proposes a way to cloak planets, as well as a way to broadcast a civilization’s existence. Even if we’re not manipulating our own signal in this way, it doesn’t mean other planets out there aren’t. It’s possible what we see as we scan the universe for other habitable planets has been engineered to disguise or highlight the existence of other civilizations.

Tracking transits to find other planets

Before we talk about how to hide a planet from distant voyeurs, consider the best way we’ve figured out to find one.

Humanity’s most successful technique for detecting other planets is the transit method. A transit occurs when a planet appears to pass in front of its parent sun, blocking out some of its starlight for a few hours. So if we have our telescopes trained at one part of the universe and a star seems to fade out for part of a day, that tells us that a planet has temporarily come between us as it goes about its orbit.