Y:        We are closer than ever to finding inhabited worlds. When an alien planet passes in front of its star, an event that's called a transit, there is a small dip in the intensity of starlight that astronomers use to detect the planet. They hope to measure the composition of a planet's atmosphere by analyzing how starlight changes during a transit. This will give us key clues about whether the planet supports life. Once we know where the life‑bearing planets are, we can focus our search for extraterrestrial civilizations.

D:        But, Yaël, what if the aliens are hiding from us?

Y:        Don't be silly, Don. How do you hide a whole planet?

D:        Its easier than you think. In 2016 two astronomers from Columbia University published an analysis. They found aliens could cancel the light dip that reveals their planet with lasers.

Y:        But wouldn't that take an absurdly powerful laser.

D:        Surprisingly, it wouldn't. The researchers calculated that just thirty megawatts of laser power would be enough to hide from the Kepler Space Telescope's searches. That's less power than seventy homes use in a year. To hide from a more advanced telescope might take ten times more power.

Y:        Don, science is about claims that can be tested by experiment. The hypothesis that aliens are hiding isn't testable.

D:        True. The astronomers where looking for ways aliens might signal their presence during a transit. They want to analyze transit data for signs of alien signaling. Along the way, they discovered how easy it would be to hide from detection.

Y:        Why would they want to hide?

D:        Yaël, we don't know what's out there. If we did, maybe we would want to hide too.