There’s always that puzzle – if conditions were such that life could arise on this planet, and the universe is so vast that there must be similar conditions out there, and given the unfathomable amounts of time for that to happen, is it really likely or even possible that this is the only place it ever happened? And if life is actually common, how could it be that we have never detected it? One answer to the puzzle would be if sophisticated life is out there, even relatively nearby, and doesn’t want to be detected by us for some reason.

Serious people at serious universities like Columbia study this, the technology side at least if not the existential questions. If aliens are hiding from us right now, here’s one way they might be doing it. Or if we thought there was somebody bad out there (one of those infinitesimal probability, infinite consequence risks that are hard to wrap your head around) and wanted to hide, here is how we could try to do it.

A Cloaking Device for Transiting Planets

The transit method is presently the most successful planet discovery and characterization tool at our disposal. Other advanced civilizations would surely be aware of this technique and appreciate that their home planet’s existence and habitability is essentially broadcast to all stars lying along their ecliptic plane. We suggest that advanced civilizations could cloak their presence, or deliberately broadcast it, through controlled laser emission. Such emission could distort the apparent shape of their transit light curves with relatively little energy, due to the collimated beam and relatively infrequent nature of transits. We estimate that humanity could cloak the Earth from Kepler-like broadband surveys using an optical monochromatic laser array emitting a peak power of ∼30 MW for ∼10 hours per year. A chromatic cloak, effective at all wavelengths, is more challenging requiring a large array of tunable lasers with a total power of ∼250 MW. Alternatively, a civilization could cloak only the atmospheric signatures associated with biological activity on their world, such as oxygen, which is achievable with a peak laser power of just ∼160 kW per transit. Finally, we suggest that the time of transit for optical SETI is analogous to the water-hole in radio SETI, providing a clear window in which observers may expect to communicate. Accordingly, we propose that a civilization may deliberately broadcast their technological capabilities by distorting their transit to an artificial shape, which serves as both a SETI beacon and a medium for data transmission. Such signatures could be readily searched in the archival data of transit surveys.