August 24

How Do We Search For Extraterrestrial Life?


Posted by Gonzo on August 24, 2023 10:46 AM

For eons, scientists and astronomers have been captivated by the tantalizing question: How do we search for extraterrestrial life? Beyond mere speculation, the quest to uncover life outside our blue planet has evolved into intricate, multi-faceted research. Traditionally, the exploration pivots on hunting for biological biosignatures, essentially scouring the universe for locations that echo Earth’s unique biochemistry and favorable environmental conditions. Yet, this anthropocentric lens, while grounded in our own experiential knowledge, might be limited in its reach. Considering the vastness and diversity of the cosmos, life forms on other planets may not adhere to our terrestrial norms, prompting the need for a more expansive, and possibly unconventional, approach to answering the age-old question: How do we search for extraterrestrial life?

Radio Telescopes

Astronomers have traditionally used radio telescopes to search for signs of extraterrestrial life by detecting low-energy electromagnetic spectrum waves not visible to human eyes; such radio waves emanate from cosmic sources like stars and planets.

Radio telescopes work similarly to visible-light telescopes in that they use dishes to collect and transmit radio wave energy to receivers; however, due to their larger dishes size radio telescopes can point at much greater distances than their visible-light counterparts can.

Radio astronomers employ special software designed for processing massive amounts of data produced by their radio telescopes, which can take hours for even a relatively simple set of observations. The software converts radio waves into signals that computers understand, then stores it on magnetic disk for later analysis.

Scientists studying star systems frequently examine them for potential biosignatures of life; for example, chemical compounds which could reveal metabolic processes of species. They also look out for technosignatures like radar and radio transmissions which might signal civilizations communicating with us or reaching technological levels similar to our own.

Astronomers are currently exploring methods of searching more broadly for extraterrestrial life forms. One idea being considered by researchers is creating a network of radio telescopes worldwide which could function like one large interferometer telescope.


Although none of the exoplanets we’ve discovered so far show signs of E.T. life (or life in general), thanks to studies of atmospheric gases like oxygen and methane we now know where to search next for signs of life (or E.T). Astronomers use various techniques such as directly imaging these planets or indirectly searching them using transit method or radial velocity surveys as methods of discovery.

Radial velocity surveys employ gravitational effects from orbiting planets to detect periodic shifts in light from stars around which these planets orbit, providing evidence for them. This technique has led to the discovery of thousands of exoplanets including those discovered by NASA’s Kepler and TESS telescopes as well as 51 Peg b discovered by our Swiss colleagues and many more planets.

Transit Method of Detection for Exoplanets | Citizen Scientists Welcome


Searching for extraterrestrial life doesn’t involve simply finding E.T. on another planet; we are after more complex lifeforms such as microbes or plants which still inhabit or once existed on an alien world, such as microbes that left behind biosignatures using exoplanet-hunting telescopes – such as chemical signatures that reveal life on distant worlds; biosignature patterns can include chemical, isotopic, mineral and morphological signs which allow us to detect life on distant worlds.

Astronomers estimate there are at least 40 billion Earth-like exoplanets orbiting their stars within the habitable zone, so finding life may not be too far-fetched. Unfortunately, however, many potential roadblocks could prevent successful biosignature searches; one being that their biosignature may be misconstrued as environmental noise or non-biological processes (including racemization of chemical compounds or geologically produced gases and mineral deposits). A second concern is that many reports claiming possible biosignatures do not withstand critical evaluation, leading to many reports being discredited or dismissed outright as unprobable reports.

An additional issue is that atmospheric biosignatures may be difficult to spot with current telescopes, especially when the target is far away. Future telescopes such as the Giant Magellan Telescope, Thirty Meter Telescope and European Extremely Large Telescope will likely be much more powerful, and can scan planet surfaces for biosignatures such as methane and oxygen that have out-of-thermodynamic disequilibrium levels.


Searches for technosignatures are one subset of an effort to locate extraterrestrial intelligence (biosignatures). While both efforts point in the same direction, they are pursued separately by different groups of scientists. Frank, who leads CATS group, is among those advocating for a unified approach to exoplanet science that includes technosignature searches.

He suggests that biosignatures and technosignatures should not be seen as competing entities, and uses similar detection methods for both. He claims radio telescopes could detect solar collectors or artificial surfaces at great distance using radio telescopes; similarly, biosigatures search heuristics like isolating signal sources can also be applied to technosignatures searches.

Artificially produced gases like hydrogen and methane could also be detected using appropriate instrumentation. Artifacts such as spacecraft could also be identified, though their construction would require sophisticated technology for interstellar distances.

Frank and others remain hopeful that their search for technosignatures will prove fruitful despite all of its complexities, though they acknowledge it will likely prove challenging to determine whether signals we detect come from alien life forms; consequently, Drake equation (which estimates how many planets host intelligent life in our Milky Way galaxy) may no longer apply here.

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