If advanced alien civilizations exist they might place intelligent monitoring devices on or near the worlds of other evolving species to track their progress. Ronald N. Bracewell first advanced the sentinel hypothesis in 1960 paper. Such a robotic sentinel, very much in the line of the well-known Arthur C. Clarke’s Monolith, might establish contact with a developing race once that race had reached a certain technological threshold, such as large-scale radio communication or interplanetary flight.
Looking for such Bracewell probes offers a number of advantages over traditional SETI. Where might they be hiding? A promising location to search for them lies among the co-orbital objects. In a paper published this month, James Benford argue that we should move forthrightly toward observing those extraterrestrial “Lurkers”
Co-orbitals are attractive targets for SETI searches because of their proximity. We should move forthrightly toward observing them.
The most attractive target is Earth’s Constant Companion 2016 HO3, the smallest, closest, and most stable (known) quasi-satellite of Earth. Getting there from Earth orbit requires a delta-v of about 4.5km/sec. It approaches Earth annually, in October. China has announced they are going to send a probe to 2016 HO3.
A recently discovered group of nearby co-orbital objects is an attractive location for extraterrestrial intelligence (ETI) to locate a probe to observe Earth while not being easily seen. These near-Earth objects provide an ideal way to watch our world from a secure natural object. That provides resources an ETI might need: materials, a firm anchor, and concealment. These have been little studied by astronomy and not at all by the Search for Extraterrestrial Intelligence (SETI) or planetary radar observations. I describe the objects found thus far and propose both passive and active observations of them as possible sites for extraterrestrial (ET) probes.Benford, James. ‘Looking for Lurkers: Co-Orbiters as SETI Observables’. The Astronomical Journal, vol. 158, no. 4, Sept. 2019, p. 150. Institute of Physics, doi:10.3847/1538-3881/ab3e35.
Featured Image: An Open letter to Alien Lurkers, by David Brin, Ph.D (fun reading)