The Reciprocal Transit

The Reciprocal Transit: Look who might be watching

Caleb Scharf

The idea that we might want to pay particular attention to places that could, in turn, be staring back at us, is not new in itself. There has even been intriguing work done by my colleagues David Kipping and Alex Teachey positing that advanced civilizations might use knowledge of reciprocal transits to signal or cloak their presence. But the Kruse et al. work is the first that I’m aware of to present a substantial list of candidates and to run the numbers on what the reciprocal transits might look like. This accounts for the small differences in orbital tilt of the planets around our Sun. For example, only one of the studied exoplanetary systems could witness the transits of three Solar System worlds – Jupiter, Saturn, and Uranus - due to the extremely close, 2 in a million, angular alignment required.

The most provocative candidate is a star with four detected exoplanets that, if anyone is looking, would be able to detect a single planet around the Sun. That planet is Earth, with a 365-day orbital period in the nominal habitable zone.

With the renewed interest in SETI these days, and the idea of looking for technosignatures, it seems that we’re starting to find some of the prime targets for proper scrutiny. Simply because these might be the places where there’s somebody, or something, already scrutinizing us.