Searching for technosignatures - signs of technology on a planet that we can see from afr - remains a difficult task. There are so many different factors to consider, and we only have the technological capabilities to detect a relatively small collection of them. A new paper, available in pre-print on arXiv but also accepted for publication into The Astrophysical Journal Letters, from Jacob Haqq-Misra of the Blue Marble Space Institute of Science and his co-authors explores some of those capabilities by using a framework they developed known as Project Janus that estimates what technology will look like on Earth 1,000 years from now in the hopes that we can test whether or not we can detect it on another planet.
Project Janus, the underlying idea of which we’ve reported on before, though we didn’t call it by that name, defines ten different scenarios for what Earth will look like in 1,000 years. They range from an industrial dystopian with levels of carbon dioxide in the tens of thousands to an ecological wonderland essentially indistinguishable from pre-industrial Earth. It’s important to note that in all these scenarios, there are still humans around - there’s no consideration for what would happen to the atmosphere of an exoplanet if civilization collapses completely in the next 1,000 years.
In the paper, the authors set a baseline of looking at an Earth-Sun analog about 32.6 light years away, and then trying to determine what, if any, technosignatures we would see as a result of the further development of the civilization on that planet down that particular technological pathway. They then analyze if we would be able to see any of them using four different existing or upcoming observatories.
Fraser interviews Dr. Jacob Haqq-Misra - the lead author on the paper.The most obvious candidate for this type of search is the Habitable Worlds Observatory (HWO) - NASA’s next flagship telescope that is specifically designed to look at the atmospheres of habitable worlds. Nitrogen Dioxide (NO2), a pollutant caused by heavy industrialization, would be noticeable to HWO in eight out of the ten scenarios. In some cases, where the civilization has developed into a planet-covering city (known as an ecumenopolis), HWO might even be able to detect the sodium emission lines from artificial lighting. However, in the more ecologically friendly scenarios, it would struggle to differentiate between a technologically advanced planet and one that simply harbors cellular life.
Radio astronomy is another fertile field for technosignature hunting. The Square Kilometer Array SKA, which will be the most powerful radio telescope ever created when it comes online in 2028. However, radio waves are notorious for losing power over large distances, and the authors determined that, unless a civilizations intentionally is sending radio frequency messages directly to us in an effort to communicate, even the SKA wouldn’t be able to differentiate signals used to communicate to the civilization’s own space probes or anything equivalent - at least not without an absurd amount of uninterrupted observational time. Admittedly, two of the more advanced industrialized scenarios actually do involve civilization actively sending messages to other potential civilizations, so it’s not completely far-fetched that SKA might be able to find something. But there are a whole lot of assumptions in that hope.
LIFE itself, or the Large Interferometer for Exoplanets, is the next observatory on the list. This mission concept from ESA is designed to operate as a very long baseline interferometer in space, would be capable of detecting plenty of industrial pollutants, including chlorofluorocarbons (CFCs) and carbon tetrafluoride (CF4), both of which would be indicative of an industrial civilization - CF4s in particular would be indicative of large-scale agriculture, which is present in two Project Janus scenarios. While still on the drawing board, this concept is promising in its ability to detect these very specific types of technosignatures.
Fraser interviews Dr. Slava Turyshev, one of the biggest proponents of the Solar Gravitational Lens TelescopeThat leaves us with the most ambitious of the four observatories - the solar gravitational lens (SGL) observatory. This observatory is still just a concept and, while its received increasing research attention, doesn’t have any structured support from any space agency, let alone a planned launch date. But, if brought to life, it would travel 600 times farther away from the Sun than the Earth is and use the gravitational lens of the Sun to amplify the signal from an interesting exoplanet.
Where a massive observatory like HWO would only be able to see a pixel or two of an exoplanet, the SGL would be able to create an entire (admittedly low resolution) image of it. This could include massive structures like orbital rings or urban sprawl in an ecumenopolis. This is by far the most powerful of the observatories, but also the one that is farthest out in time - in fact it might take a significant portion of the thousand years of technological development between us and the civilizations theorized in Project Janus to get data back on them. Traveling to the SGL itself is a 70 year endeavor with current technologies.
Ultimately, this paper provides a framework to understand what we should be looking for in terms of potential technosignatures. Keeping them in mind while these great observatories go through their development cycle would be helpful. Because eventually one or more of them could lead to one of the greatest discoveries humankind could possibly make - that we’re definitively not alone.
Learn More:
J. Haqq-Misra, R . K. Kopparapu, & G. Profitliotis - Projections of Earth’s technosphere: Strategies for observing technosignatures on terrestrial exoplanets