Dirk Schulze-Makuch - The Search For Biosignatures Is Hard. Should We Look For Technosignatures Instead?

The Search For Biosignatures Is Hard. Should We Look For Technosignatures Instead?

Should we be searching for life on other planets, or technology?

Key Takeaways

• Our quest to find life on other planets is currently tuned to biosignatures. But this search is far from straightforward, and there is always the risk of false positives.
• The best scenario we can hope for is to find a complex biosphere that produces multiple lines of evidence pointing to life. But what if we focused instead on technosignatures — evidence of technological activity from advanced civilizations?
• If a planet hosts technologically advanced life, it stands to reason that it would also host less complex life forms, and we should expect to see both kinds of signatures.

Episode Transcript

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The following in foecast is a presentationof the XOON Broadcast Network, XOON TV
channel and Roma McConnell Media Company,broadcasting from Canada to the world and beyond.

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The search for biosignatures is hard,should we look for technosignatures instead?
In our quest to detect life onother worlds? The current state of the
art is to look for biosignatures,specific chemicals or combinations of chemicals that suggest
in earthlike biology in a planet's atmosphereor on its surface. Chlorophyll is a

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good example. It would certainly grabour attention if we saw a planet showing
the so called vegetation red edge,the rapid change in reflectance at near infrared
wavelengths that is a marker of thepresence of vegetation. Many more molecules have
been suggested as biosignatures, specifically thoseunlikely to be produced in large quantities by

(01:04):
non biological processes false biosignatures. Discoveringa biosignature on another planet may not be
straightforward. However, there are twomajor problems, the first of which relates
to detection levels. A truly conclusivediscovery will probably require finding a large biosphere

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producing specific molecules in great quantities.For an Earth type biosphere, that would
mean widespread photosynthetic life on the planet'ssurface. The other problem is the possibility
of false positives. Since we willhave very limited information about any exoplanet for
the foreseeable future, the danger ofmisinterpretation will always be there. A planet's

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environment could be strange, unlike anythingwe know, and it might produce chemical
compounds through some abiotic process that onEarth can only be produced by biology.
The best scenario we can hope foris to find a complex biosphere that produces
multiple lines of evidence pointing to life, say something equivalent to a tropical rainforest

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on Earth. In such a case, we would expect to see large quantities
of chlorophyll or of some other lightharvesting molecule such as rhodopsin or carotenoids.
If we are lucky, we mightalso be able to observe a vegetation red
edge. Its exact wavelength would dependon the specific life harvesting molecule. In
addition, a rainforest would interact withthe geosphere of the planet, affecting its

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climate, especially the global cloud distributionand regional precipitation patterns. A rainforest also
would release volatile organic compounds. Allof these indicators could in principle be detected
by future telescopes artifacts in space.So far, we've been talking about finding
plant life on other worlds, butdiscovering technici natures evidence of alien technology might

(03:01):
be easier and more straightforward. Arecent paper by Jacob hack Mishra and colleagues
from the Blue Marble Space Institute ofScience, published in the journal Acta Astronautica,
provides a very good overview of currentspeculation. In that regard, the
authors distinguish among different kinds of technosignatures. These could result from energy intensive illumination,

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surface modifications, atmospheric pollution, nonterrestrial artifacts, or megastructures. An
example of energy intensive illumination would becity lights at night. In principle,
a single candle can be seen frommore than a mile away if there is
no other light source to compete with. City lights are obviously a lot brighter,

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but given all the stars in thesky, it would still be a
challenge to pick out some alien metropolison a planet several light years away.
Still, the authors estimate that thelights from an alien civilization may be visible
using upcoming telescopes such as ludwar LargeUltraviolet Optical Infrared surveyor. That is,
if the planet has twelve times theamount of urbanized area that Earth does,

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and depending on what type of lightingthe aliens use, surface modifications on a
planet could be detectable as well ifthey are large enough. Mnusby Lingam and
avy Lobe suggest that large scale photovoltaicarrays used to harness energy from other stars
might have distinctive spectral features that futuretelescopes could recognize. Another possible technosignature is

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atmospheric pollution on our own planet.An example of this is the chlorofloor carbons
that have damaged our atmospheric ozone layer. Here we have to guard against anthropocentrism.
Alien civilizations might have no use forspray deodorants or refrigerators, but if
CFCs were detected in high amounts onanother planet, they would be a convincing

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technosignature. Artifacts like spacecraft are anotheroftmentioned technosignature, although these would be very
difficult to detect over interstellar distances.But even if the spacecraft themselves are not
detectable, their propulsion systems might be. We do not know what kind of
engine an interstellar vehicle would have,but one powered by nuclear fission, nuclear

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fusion or antimatter might be detectable.Megastructures like Dycen spheres are often considered among
the most easily detectable of technosignatures,in part because they would be so massive.
However, as Brooks, Harrup andI have shown, such giant structures
would not be gravitationally stable and theywould take too much mass to build a

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so called Dycen swarm with millions ofenergy Harvesting satellites orbiting a star would be
more practical, but it would alsobe much more difficult to detect from a
distance. Technosignatures versus biosignatures. Eventhough we have discovered thousands of exoplant and
it's already we have yet to seea single biosignature or technosignature. There have

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been a couple of tantalizing false alarms, however. Several years ago, dips
in the light curve of Tabby sStar led to speculation about an alien megastructure,
but the fluctuations were eventually explained asthe breakup of one or several comets.
The mysterious well signal detected by aradio telescope in nineteen seventy seven could

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have been an intercepted spacecraft communication,but there is still no way to settle
the matter for shore. So wheredoes that leave us? I think the
best strategy is to search candidate planetsor moons both for biosignatures and technosignatures.
If a planet hosts technologically advanced life, it stands to reason that it would
also host less complex life forms,and we should expect to see both kinds

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of signatures. In that case,the chance for a false positive detection would
be very much reduced because we wouldhave evidence produced by independent methods. If
we see biosignatures but not technosignatures,that could suggest a planet where advanced life
never evolved. On the other hand, if we detect technosignatures but no biosignatures,

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we might be looking at a colonyof artificial life forms but no biology.
Either of these cases might lead tofrustration, though we would always have
to wonder whether we had found afalse positive. To listen to all the
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