Recently experts gathered online for a digital conference in which they discussed possibilities for detecting signs of alien technological civilizations – so called “technosignatures”. Being an enthusiast, I have heard of many of these before, but there were a lot of new ideas coming out of that meeting as well. Here is the preprint, with all the technical information. I think collectively this is a compelling case for NASA and other agencies to include the search for technosignatures as a part of their mission.

The most obvious technosignature is radio signals, most likely deliberately broadcast, either out into the universe or even directed at Earth (if they have detected our own technosignatures). This is the object of SETI (The Search for Extraterrestrial Intelligence). NASA briefly funded a SETI project, but then pulled funding. The effort continues, however, with other funding. I have interviewed Seth Shostak from SETI several times and he makes a couple of points worth emphasizing here. One is that SETI is simultaneously doing a lot of non-SETI astronomy. They are essentially doing radio astronomy but looking at any data in such a way that it could detect an alien signal.

The members of the recent meeting also considered what they call “synergies” or ancillary benefits for each of the techniques they discuss. This is critical, I think, because it means even if we never detect an alien technosignature, the effort would not have been wasted. We will have accomplished a lot of meaningful astronomy in the meantime. I would argue it wouldn’t be wasted in any case – negative results from an experiment are still results. We would have gathered lots of data about how rare technological civilizations are in the universe. But if you look at the table of discussed techniques in the paper, each one has a listed potential synergy. In fact, they also list existing astronomical data that can be searched for technosignatures.

Seth also pointed out that if we did detect an alien message hiding in radio signals, we would very likely not be able to read it. This is because radio signals get weaker with distance, and at some point they would be lost in the background radio noise. The more powerful the initial radio signal, the greater its range. The current authors call this the “cosmic footprint” of each technosignature, and coin the term “ichnoscale” to measure it. For example, they give radio astronomy a 10 kpc (kiloparsec) ichnoscale for detecting alien signals.

What we would have to do, Seth says, if we did detect a potential radio technosignature is literally build a new radio telescope specifically to resolve the alien signals – some array bigger than we currently have. Imaging waiting for that to be built, knowing we have an alien radio signal to read.

So these are the two guiding concepts of the conference – there are many potential technosigntures we could detect, each with their astronomical synergies and each with their cosmic footprint, as measured on the ichnoscale. Again, all the details are in the linked paper, but here is the TLDR version. (I will give the ichnoscale for each method I mention in parentheses)

Some methods require looking directly at an exoplanet, even a transiting exoplanet. This could include using spectroscopy to look for industrial gas in the atmosphere (10 pc) or looking for dark side illumination from artificial lights (10pc). The synergy here is atmospheric analysis, and perhaps finding biosignatures – signs of life itself.  Other methods involve looking at the effects of transiting objects on the light of the star, similar to how we find some exoplanets. One signature that can be detected this way is a Clarke Belt (names after Arthur C. Clarke) – this is a ring of artificial satellites around a planet. Think of how many satellites we already have orbiting the Earth. Some of these will occur at discrete distance, such a geocentric orbit (1kpc). We might also detect large alien objects orbiting the star (1kpc). The synergy with any transit method analysis is finding further exoplanets and even exomoons.

Alien technology may also involve powerful laser pulses, propelling solar sails, for example, or even as a method of communication (100 kpc).

Large alien artifacts, or anything that uses lots of energy, will generate waste heat, and this heat can be detected in the infrared spectrum. This includes a Dyson sphere (1kpc), or even the heat from a galactic civilization (1 mpc). If you recall, when anomalous decreases in the light from Tabby’s star was detected, some proposed that this could be from a Dyson sphere (or Dyson swarm) – this is an array of solar collecting devices around a star that an advanced civilization might use for power. Once such an array is large enough, it would significantly block the light from the star. It would also glow in the infrared spectrum. So, one of the first things astronomers did was look at Tabby’s star to see if there were any IR emissions that might be from something technological – and found nothing. It turns out the dips in light are likely due to a swarm of comets.

In addition to looking for technosignatures outside our solar system, the authors also considered the possibility of looking for alien artifacts in our own system. Alien probes may be watching us right now, or may be left over from visits billions of years ago. This could include artifacts on the moon, asteroids, or other bodies, or probes in an Earth co-orbital (all 1AU). The synergy here is detecting near Earth objects (NEOs), dwarf planets, and other objects in our own solar system.

Collectively the conference goers make a compelling argument that the search for technosignatures is good science that can be done efficiently alongside other science, and is a worthwhile investment. I agree. Right now we only have one data point of a technological civilization in the universe. So we basically have no idea how common or rare they are. Once we get even a second data point we will have a much greater idea of whether or not we are alone in the universe, the universe is teeming with life and buzzing with alien tech, or where between these extremes reality lies.