Plans are in the works toin search of alien life. But what if another civilization has already launched a similar mission to observe Earth without our knowledge?
James Benford, who authored the definitive book on high-power microwaves and has written about the search for extraterrestrial intelligence, says in a draft paper that 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."
In the paper, which has yet to be peer-reviewed, Benford refers to alien eyes in (or above) the sky as "lurkers." He goes on to give several examples of co-orbital objects (all of which are probably asteroids) that could be worth checking for them.
Benford runs a company called Microwave Sciences that designs and consults on high-power microwave systems. He often collaborates on his SETI (search for extraterrestrial intelligence) work with his twin brother Gregory Benford, a noted science-fiction author, and his son Dominic Benford, a scientist at NASA.
While the vast majority of asteroids orbit the sun in a wide belt between Jupiter and Mars, some wander farther into the inner solar system near Earth's orbit.
There's an even rarer type of object called a "quasi-satellite" that may spend centuries or longer making often oddly shaped orbits around our planet. One example is asteroid 2016 HO3, also known as "Earth's Constant Companion," which is detailed in the below video from NASA.
The idea that an extraterrestrial spy satellite might be hidden near our planet isn't new. The late Stanford electrical engineering professor Ronald Bracewell proposed in an oft-referenced 1960 paper that advanced alien civilizations might place artificial intelligence near inhabited planets to monitor the progress of less advanced worlds and perhaps make contact at some point.
Of course, we have observatories keeping watch on the thousands of known near-Earth objects and discovering new ones almost daily. A handful of asteroids has been visited by spacecraft, includingthat are currently orbiting space rocks. So far, such observations have yielded no evidence of anything alien or artificial.
But the co-orbital objects that Benford said deserve more attention are relatively new discoveries, having come to our attention in the past decade for the most part. And we may not have noticed anything because any sort of automated alien spy system placed long ago could be dead or lie dormant for long periods of time, making it difficult to detect.
"This means we should consider searches over decades-long time scales," Benford's brother Gregory, himself an astrophysicist, wrote Tuesday in the space blog Centauri Dreams. "Lurkers from the far past may have done their duty and slowly failed ... the ruins of Lurker installations, including mining for resources on nearby orbiting sites, may be visible, even though their animating intelligences are long gone."
Much SETI work focuses on looking beyond our solar system and essentially listening to distant stars for signs of life.
But if E.T. were already listening and watching us from a technological lookout post near Earth, it makes the search easier in a number of intuitive ways. First off, shorter distances mean not having to wait the years required for any sort of data to travel back to Earth from another star system. Sending a probe to the nearest star beyond the sun would take at least 20 years and then we'd have to wait at least four more years for any data or imagery from that probe to be transmitted.
James Benford also argues that it's much easier to prove or disprove some alien construction is in a near-Earth orbit versus observations from other stars that can be nearly impossible to confirm or falsify.
"We can observe them, ping them with radar, transmit messages to them, send robotic probes to them and visit them with human spacecraft missions," writes Benford, who says he plans to submit his paper to the Astrophysical Journal.
Douglas Vakoch, president of METI (Messaging Extraterrestrial Intelligence) and formerly of the SETI Institute, which is funded in part by NASA, tells me there's also another potential advantage to looking for alien life hanging out on nearby asteroids.
"The notion of searching for lurkers by transmitting to likely locations in our solar system provides an intriguing possibility for finding common ground in Active SETI," he said, referring to the debate over whether humanity should actively try to make itself visible to potential advanced alien civilizations. "Some of the same individuals who have been cautious about Active SETI transmissions to other stars are advocates of pinging nearby aliens -- on the grounds that the extraterrestrials would already know we are here."
One of the people who has emphasized the potential risks of actively trying to contact E.T. beyond the solar system is Benford himself. In a 2014 paper, he advocated for a moratorium on Active SETI/METI until an international consensus could be reached on the idea.
In other words, while they might disagree on the wisdom of transmitting to the stars, as, both Vakoch and Benford can be excited about trying to contact aliens who may already be nearby.
"What have we to lose by checking out these objects?" Benford writes. "Nobody has really looked at these co-orbitals, other than orbital calculations and faint images. We know almost nothing about them."