Since the search for extraterrestrial intelligence began, astronomers have been trying to answer the question “Are we alone in the universe?” in two ways: by listening for deliberate messages, and by looking for physical evidence – the products and byproducts – arising as a consequence of extraterrestrial civilization.

The latter search, called xenoarchaeology on this site, has explored a number of strategies such as hunting for orbiting probes, artificial structures on planetary surfaces, and astroengineering projects such as Dyson spheres.

Paul Davies of the Beyond Center at Arizona State University has just published a paper in Acta Astronautica promoting the search for more subtle traces of nonhuman civilization, and asking that the entire scientific community be on the lookout. His paper covers a number of astrobiological issues such as the need to refine the Drake equation, but I’m focusing here on the search for technosignatures.

Davies calls this search for subtle evidence of intelligent agency astroforensics, after the criminal science. It’s an apt description, but a quick google search reveals two existing definitions:

  • application of forensic evidence management principles in astrobiology; and
  • the search for astronomical explanations for historic events.

Perhaps a better term could be decided upon to avoid confusion?

Assuming that there is no particular reason why our own period would favour the rise of intelligence (what Milan Cirkovic has called astrobiological phase transition), Davies argues that extraterrestrial civilizations would arise at a uniform rate over time, most likely in the deep past.  The suggestion that ETI made contact with Earth in the deep past might be called palaeocontact if that wasn’t indelibly stained with ancient astronaut associations.

This is not a new line of reasoning, of course, but it’s interesting to see Davies suggest that the search for nonhuman remains include the solar system, given Ben McGee’s recent paper on the subject.

Davies lists a number of ‘traces’ that might survive a 100 million year period (but notes that “all bets are off” when it comes to guessing the technological by-products of a 10 million year old civilization):

  • nuclear waste
  • large-scale mineral processing or geo-engineering
  • biotechnology or a shadow biosphere
  • DNA-encoded “messages in bottles”

Vast storehouses of data are being developed in many fields, and Davies argues that searches for anomalies can be conducted cheaply, even if they seem improbable.

Surprisingly, Davies doesn’t bring up the search for technosignatures outside the solar system, such as those listed here by Robert Freitas (and more recently suggested by Duncan Forgan). Davies also seems to be unaware of Alexey Arkhipov’s apparently unique suggestion that extraterrestrial space junk could be transmitted over interstellar distances, such as in his papers Extraterrestrial Technogenic Component of the Meteoroid Flux, and On the Possibility of Extraterrestrial-Artefact Finds on Earth.

It’s refreshing to see a scientist of Davies’ stature endorsing the search for extraterrestrial artefacts, particularly within the solar system. Whether scientists from outside a narrow field of interest will begin to conduct searches of their databases for anomalies is questionable, but we can hope.