If there's an advanced civilization in the TRAPPIST-1 system living on multiple worlds, there's a way to eavesdrop on their conversation from world to world. Researchers directed the Allen Telescope Array at the TRAPPIST-1 system during times of "planet-planet occultations," when two of the worlds in the system are aligned with Earth and their star. Communications directed at the planet could spill over and be detectable from Earth. No signals were detected.

One possible explanation for dark matter is primordial black holes. These are lower-mass black holes formed in the first moments of the universe when the conditions were hot and dense. If there are asteroid-mass black holes floating through the cosmos, a few might be here in the solar system. The only way to detect them would be to measure their gravitational interactions with planets and other asteroids. Is our current technology up to the task?