This past Wednesday Col Maybury, host of the Australian radio show The Starlight Zone, interviewed Shawn and I about covering the far side of the Moon with mirrors as a remotely detectable technosignature.

Listen to the complete (~5 minute) interview at the Starlight Zone

This idea got far more press than either of us had anticipated, so we tried to use our air time to do some damage control and clarify the idea beyond the scope of a brief news write-up. We are currently in the process of drafting the manuscript for submission.

This work is unfunded: We came up with this idea following the Pale Blue Dot III meeting as a solution to particular problems with the SETI approach to finding intelligence; however, we are not funded to develop this idea nor do we have any intentions of proposing construction of mirrors on the Moon to any funding agency. (Our global society can’t even agree upon a consistent program to address climate change issues–I seriously doubt our ability to maintain a long-term signaling project.)

Our signal is omnidirectional: A targeted broadcast such as a radio signal or laser pulse is limited because of its directionality. Our scheme, though, covers the far side of the Moon with mirrors on pivots (with dark solar panels on the opposite side) so that the albedo of the Moon can be effectively changed from 0 to 1, resulting in a 20% change in luminosity for the Earth-Moon system. This change in luminosity will be observable from almost any direction at any time and will not require a targeted broadcast.

Our signal is broadband: Because the light reflected from the Moon’s mirrors comes from the Sun, the detected change in luminosity will span a large section of the electromagnetic spectrum (depending on the particular mirrors used). This further increases our chance of success because we make fewer assumptions about the preferred observational/communicative frequency of extraterrestrials (whereas conventional SETI presumes radio beacons or other narrow-band broadcasts).

This beacon requires current and near-future technology: The mirror/solar panel pivots can be constructed with current technology. Furthermore, we are detecting new extrasolar planets every day. In 2009, Kepler will launch in search of terrestrial planets around other stars, and in the next 10-20 years the Terrestrial Planet Finder will be able to observe these planets and take spectra of their atmospheres. In other words, within the century it will be within our technological grasp not only to build such a signal but also to detect a similar signal around a distant world.

ET’s may use a similar technique: Even if we never construct a technosignature using the Moon, it is conceivable that a technological extraterrestrial society may signal their presence using a similar method. If the Terrestrial Planet Finder were to detect an Earth-sized planet around another star blinking in the prime numbers, we would at least have a hypothesis to explain this seemingly deliberate signal.