Credit: ESA/Hubble & NASA

Near our home planet Earth we should be on the lookout for “Lurkers” – possible sites for extraterrestrial probes that may be quite ancient.

Scientist James Benford of Microwave Sciences in Lafayette, California is promulgating the view that an attractive location for extraterrestrial intelligence may well be anchoring a probe to observe Earth throughout our deep past are the co-orbital objects. It would be a new way to do the search for extraterrestrial intelligence (SETI).

Imaginative searches

“Co-orbital objects approach Earth very closely every year at distances much shorter than anything except the Moon,” writes Benford. “They have the same orbital period as Earth. These near-Earth objects provide an ideal way to watch our world from a secure natural object.”

The Atacama Large Millimeter/submillimeter Array (ALMA) in northern Chile’s Atacama desert.
Credit: ESO/B. Tafreshi (

Benford has pioneered imaginative searches for interstellar communication. His first work with other family members yielded the term “Benford Beacons” — short microwave bursts to attract attention, like lighthouses.

Later, Benford pointed out using powerful electromagnetic beams to send light spacecraft, “sails,” in interplanetary exploration. Now his Lurkers proposal moves on to actual relic alien spacecraft that may have been nearby for longer than humans have existed.

Spectral lines

“Alien astronomy at our present technical level may have detected our biosphere many millennia ago,” Benford explains. “Perhaps one or more such alien civilization was drawn in recently, by radio signals emanating from our world. Or maybe it has resided in our solar system for centuries, millennia or longer.”

If we give a Lurker a full-on look-see and find nothing there, Benford adds that this gives us a profound result: no one has come to look at the life of Earth, which has been evident in our atmosphere’s spectral lines over interstellar distances for over a billion years.

Credit: CNSA

Benford underscores that the most attractive target as a Lurker is 2016 HO3, the smallest, closest, and most stable (known) quasi-satellite of Earth. And to add a little space program nudge, China in April announced they are blueprinting a plan to send a probe to 2016 HO3, he notes.

Pete Worden of Breakthrough Initiatives.
Credit: ESO/M. Zamani

Reverse engineering

Breakthrough Starshot, a Breakthrough Initiatives project, aims to send a gram-sized spacecraft to a nearby star system at around 20% of the speed of light and shows our outbound thinking to reach out to other worlds.

In reverse, as Breakthrough Initiatives Chairman, Pete Worden explains, if intelligence arose elsewhere in our galaxy, it may well have sent out similar probes. “It’s intriguing to think that some of these may already have reached our own solar system.”

To access this thought provoking paper – “Looking for Lurkers: Objects Co-orbital with Earth as SETI Observables” — go to:

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