Which Missions and Observatories can Detect Technosignatures?

The search for technosignatures has always taken a back seat in the broad search for extraterrestrial life forms. Biosignatures, such as methane in an exoplanet’s atmosphere, have long been front and center. But while we are searching for signs of biology, signs of technology might be hiding in plain sight. According to a new report from the members of the TechnoClimes conference, humanity could potentially find signs of technology by simply using data that will already be collected for other purposes. To prove their point, they came up with a list of possible technosignatures and cross-referenced them with a list of observatories that could potentially find them. The result is a framework of how to best search for technosignatures and a plethora of references for those seeking them out.

Though the report was just released in May 2022, the actual conference occurred in August 2020. TechnoClimes billed itself as “an online workshop to develop a research agenda for non-radio technosignatures.” The report is the output of one of the four objectives of the workshop – to “encourage a broader range of astronomers to consider the relevance of technosignatures to their research by serving as a resource that describes the detectability of various non-radio technosignatures with current and future missions.”

The second objective focused on developing mission concepts that could specifically look for technosignatures, which are sorely lacking so far, though we reported on some last year. The third objective focused on a framework to evaluate “non-canonical astrophysical phenomena” – in effect, data that we can’t otherwise explain and that might itself be a technosignature. The final objective is to recruit more researchers to the cause by “broadening international participation” in technosignature searches.

With the overwhelming amount of data it already has to sift through, the field will need all the help it can get. And that amount of data is only set to grow as more capable observatories come online. To understand what those observatories are capable of, the TechnoClimes participants’ framework broke both the observatories themselves and the technosignatures they could find into three major categories each.

The first observatory category is the current and recently completed missions, such as JWST, Gaia, and TESS. Next are “near future” missions that are expected to launch in the next five years, such as the Roman Space Telescope and PLATO. The final category is “future” missions that are still five or more years out and are largely still concept studies at this point. These include LUVOIR, HabEx, and Nautilus.

Technosignature categories are also divided into three main areas, with sub-categories for each. Notably, this report focuses on non-radio-based technosignatures, as the authors point out that radio-based technosignatures have already received ample attention in the form of SETI and other efforts to detect them over the past few decades.  

The first technosignature category is optical beacons. These can typically be thought of as lasers, which can be used for communication, or as a light sail, such as those under development by Breakthrough Starshot. However, they might also translate into things like fusion drives, the exhausts of which can potentially be seen for hundreds of light-years around. A wide array of observatories, ranging from already existing ground telescopes up through LUVOIR, would likely be able to detect powerful optical beacons. 

Next on the potential technosignature list is planetary technologies. This is broken down into two sub-categories, which are then broken down into even further sub-categories. Atmospheric Technosignature makes up the first sub-category, and it is further divided into a UV, visible light, and near-infrared category, as well as a mid-infrared category. Atmospheric technosignatures can be considered gases released into a planet’s atmosphere from industrial or non-biological processes.  

Humans produce copious amounts of these gases, such as chlorofluorocarbons and sulfur hexafluoride, every year. Some gases, such as nitrogen dioxide, would be detectable in visible light. While this gas has some biological causes, the amount produced by them is dwarfed by those produced by industrial processes. It should be visible around planets orbiting Sun-like stars for observatories such as LUVOIR.  

Other gases, such as carbon tetrafluoride, are more likely to be captured in the mid-infrared wavelengths by observatories such as James Webb. In fact, JWST might be able to find Earth-like levels of some atmospheric technosignatures simply on one of the TRAPPIST planets. Plenty of other atmospheric observations could prove a way to search for technosignatures, but as the authors point out, this is still an area of ongoing research.

The following sub-category of planetary technologies is artificial surface modifications. The most obvious of these would be seeing the city lights of an exoplanet. Parts of the Earth are brightly lit during the night, and even lights that are only slightly brighter could be visible to some future generation of observatories, such as LUVOIR. They might even be visible to the Roman Space Telescope, though that has yet to be conclusively proven.

Other potential surface modifications would include vast swathes of solar panels, which could be visible from far, far away, and their dampening effect on the reflected light of an exoplanet could be potentially noticeable. Alternatively, a “heat island” effect, such as a more pronounced version of the effect seen around many modern cities on Earth, could be visible in the mid-infrared range.  

Taking a step up from planetary surface modifications, the final category of potential technosignatures is known as system megastructures. These are engineered objects, such as a Dyson Sphere or Swarm, that could be large enough to have their own transit of their host star that would be detectable in visible to near-infrared light. Another way to find them would be to look for the waste heat they would inevitably produce, which should be visible in the mid-infrared range. Transits of such a megastructure should be visible by almost every currently launched and future mission. At the same time, their waste heat would be detectable by Spitzer or NeoWISE, two aging infrared observatories.

The fact that they haven’t yet been seen in the NeoWISE or Spitzer data is not evidence that they don’t exist – just evidence that no one has come up with a viable search criterion for them in that data. As the authors are quick to point out – even not finding any potential technosignatures is still a very valuable scientific endeavor because it allows the scientists to put statistical constraints on the likelihood of the existence of those technosignatures elsewhere. 

For example, there are 74 “bright” stars within 10 parsecs (~33 light-years) of Earth – most of them likely have planets. Suppose no technosignatures are found on any of them after an exhaustive search. In that case, that is more data to feed to a statistical model of the likelihood of intelligent life developing elsewhere in the galaxy. But if a potential technosignature is found, that could fundamentally alter our understanding of life as we know it. That seems worth the investment, doesn’t it?

Learn More:
Haqq-Misra et al. – Searching for technosignatures in exoplanetary systems with current and future missions
UT – Next Generation Telescopes Could Search for Intelligent Civilizations Directly
UT – NASA’s Technosignatures Report is Out. Every Way to Find Evidence of an Intelligent Civilization
UT – Technosignatures are NASA’s New Target for Detecting Other Civilizations in Space. Wait. What’s a Technosignature?

Lead Image:
Concept image showing different types of possible technosignature signals.
Credit – Haqq-Misra et al.