Biosignatures and technosignatures

Biosignatures

Highland cattle are popular with tourists who visit Scotland. You might wonder why there’s a photo of them below. We’re not in any way suggesting they might also exist on some far-off exoplanet - but cows do produce methane, which is a recognised biosignature here on Earth. And it’s possible that methane might be a sign of life elsewhere.

A biosignature is a marker of life, past or present. As this is true here on our planet, it will also be a reliable indicator of life beyond Earth. Any extraterrestrial life might be microbial or complex.

The definition is simple, but the actual task of looking for a biosignature on another planet is a complicated process. Scientists have to consider all possible alternative explanations before they can conclude that something is a genuine sign of life. It would be easy to jump to a wrong conclusion. Academics can be over-cautious to the point of sometimes being irrational - but, on the good side, they also appreciate the need for prudence and attention to exact detail.

It’s basically a matter of differentiating the non-biological processes of a planet from possible biological ones, so as to eliminate false positives. Oxygen is a good example as it isn’t exclusively produced by living things. Conversely, there’s also a danger of false negatives - where life could be present on a planet, yet undetectable.

How we evaluate whether a planet has living organisms is currently based on what we know about habitability on Earth. In other words, we’re using our own planet as a template when searching elsewhere. The presence of liquid water is an example of what we’re looking for on other planets, as a known prerequisite for life. Extremophiles - organisms which can live in extreme environments, such as volcanic lakes and sulphur springs - provide an additional category of life to search for.

Artificial lights of the midwestern United States are a technosignature of our presence Credit: NASA

Technosignatures

Technosignatures - evidence of some technology that modifies its environment in ways which are detectable - go a step further. This technology is, by necessity, produced by intelligent life. The photographic image above is an example of how we humans have modified our environment, in the form of manufactured or artificial lights that are visible at night. (Theoretically, if we’re anything to go by, there might be an over-cautious scientist out there on another planet, looking in our direction, arguing that our nighttime lights are just a bunch of excitable glow worms having an orgy - and not a technosignature. But they would have to be at the same semi-primitive level of evolution as us to be this arrogant.)

Another way of defining technosignatures is anything we would recognise as technologically-advanced activity. Of course, as it’s reasonable to assume there will be civilisations way ahead of our stage of development, we simply might not be able to detect or understand certain markers of such advanced intelligences. But, hopefully, there will be some that we can.

As yet, scientists haven’t conclusively found unshakable evidence of any biosignature or technosignature beyond Earth. That said, there are a couple of possible exceptions. There’s a preliminary suggestion that microbial life might exist in the clouds of Venus, as unexpected levels of phosphine have been detected. But we won’t know for sure until we send a physical probe with a mini laboratory to further investigate.

A very different suggestion is that of ‘Oumuamua. Whatever it was, this unusual object originated from outside our solar system, yet passed through it and by us for a short time in 2017. The details are too complex to fit into this short article, but Avi Loeb - Professor of Science at Harvard University - has brilliantly argued that the most likely hypothesis is of it being an artifact of extraterrestrial technology. As it’s now gone, we’re unable to gather additional data, but we should be prepared for any similar opportunity in the future. Avi’s recent book Extraterrestrial (February 2021) is strongly recommended for anyone interested in learning more.

Oumuamua depicted as a flat rock. But did it really look like this? Credit: European Southern Observatory/M Kornmesser

Moving beyond academic and institutional prejudice

The search for biosignatures and technosignatures is an area of rapidly advancing scientific endeavour. This current interest has been spurred on by astronomers finding over 4,000 exoplanets (and counting), including ones in habitable zones potentially capable of sustaining life. But, sadly, there’s still much academic and institutional prejudice to overcome - psychological immaturity that is unbecoming and at odds with the purity of the scientific method.

There’s been a long history of small-mindedness, but two quotations suitably indicate and summarise the situation. Although they reflect poorly on the United States, other countries have been no better. In 1992, NASA pledged $100 million over ten years to fund a Search for Extraterrestrial Intelligence (SETI) project, but the funding was cancelled less than a year later. “The Great Martian Chase may finally come to an end,” said Senator Richard Bryan of Nevada, one of its most vocal detractors. “As of today, millions have been spent and we have yet to bag a single little green fellow. Not a single Martian has said ‘Take me to your leader’, and not a single flying saucer has applied for FAA approval.”

More recently, Jason T Wright - a professor of astronomy and astrophysics at Pennsylvania State University - wrote an Astro2020 White Paper titled Searches for Technosignatures: The State of the Profession. It was supported by 126 endorsers from across the US and overseas. Wright expressed dismay at the lack of support for searches for technosignatures before stating: “A major source of this issue is institutional inertia at NASA, which avoids the topic as a result of decades-past political grandstanding, conflation of the effort with non-scientific topics such as UFOs, and confusion regarding the scope of the term ‘SETI’.”

Our organisation is leading the field when it comes to the topic of psychological avoidance - including how this frustrates human potential and limits access to better psychological health, affecting all walks of life. So it’s refreshing to see the word “avoids” used in such a blunt and appropriate context. Avoidance, together with hypocrisy, is the elephant in the room - a clear sign of human immaturity. Those who pride themselves on being intelligent, capable of rational thinking, should know better, yet don’t.

A new generation of ground-based telescopes with higher resolution capacity - together with improved space telescopes, such as the James Webb Telescope (scheduled for launch later this year) - will make the search for biosignatures and technosignatures a bit easier. It will only take the discovery of a single, confirmed case to definitively answer the question “Are we alone?” The chances are, that once we find one, many more instances of life on other planets will follow.

Written by Victoria de las Heras, 7th May 2021