A new chapter in the search for extraterrestrial life

The Estonian researcher, Mihkel Pajusalu, and his American colleagues have conducted a new type of scientific experiment at the Massachusetts Institute of Technology and conclude that there are grounds for looking for life from a lot more celestial bodies than previously thought.

This article is published in collaboration with Research in Estonia.

Thus far, the dominant paradigm has been to look for signs of life on planets with Earth-type atmospheres. Mihkel Pajusalu, a senior research fellow at Tartu Observatory in Estonia, was behind the experiments that led to the breakthrough in a recent study that demonstrates the need to look for life in completely different conditions. “We see the same base building blocks everywhere. Where they lead to life and where not – that is the question,” Pajusalu, whose research has already gained an international interest, said.

We are comparatively well acquainted with what is going on within our own inner solar system, but we know far less about the celestial bodies or exoplanets formed around other stars because we yet cannot detect what is happening on their surface. We can, however, use the large telescopes in space to analyse how their atmospheres absorb light. Based on this information, scientists can calculate which gases are present.

Exoplanet in a glass vial

Working as a postdoctoral student at the reputable Massachusetts Institute of Technology (MIT) in Sara Seager’s group, Pajusalu, together with other team members, had the idea to use the conditions expected in the atmosphere of distant planets as a recipe and create various gas cocktails in the lab, which could be populated by small yeasts and escherichia coli.

“Although the end result is simple, developing and carrying out the experiment actually took about three years,” Pajusalu explained. It is a new type of experiment and was, in turn, made possible thanks to an oxygen sensor created in the MIT work group by Pajusalu.

The Massachusetts Institute of Technology in Cambridge, Massachusetts. Photo by the Massachusetts Institute of Technology.

The experiments showed that several organisms that are not used to a hydrogen-dominated atmosphere, can still successfully grow in it. In an article published in Nature Astronomy, Pajusalu and his American colleagues conclude that pursuant to this, there are grounds for looking for life from a lot more celestial bodies than previously thought.

“Currently, a paradigm that life should only be looked for in places with lots of oxygen has existed for a long time. However, using current technical means, it is practically impossible to measure the exact oxygen concentration on Earth-sized exoplanets,” Pajusalu noted.

“The result of our study gives grounds for searching for life also from planets with hydrogen-rich atmospheres and studying these planets is already becoming possible with space telescopes. Therefore, we now have a practical way for looking for extraterrestrial life, which would have been otherwise postponed for a long time.”

Cosmic exchange of matter

The chemistry of interstellar space seems to be the same everywhere and the periodic table of elements applies in other galaxies as well. Exciting examples on the exchange of matter between solar systems arrive with each comet and asteroid, which disintegrate during their journey and leave behind dust particles and larger pieces, and thus transfer matter from one solar system to another.

Would the reverse be possible, i.e. sending a yeast colony to another exoplanet with a suitable atmosphere? According to Pajusalu, even the exoplanets closest to us are still too far away for considering this theoretical possibility, although projects like Breakthrough Starshot have been proposed. However, he hopes that resulting from the recently published study, it will be easier to get observation time on space telescopes and continue modelling in the lab based on new data.

Estonia’s increasing role in space missions

Anu Noorma, the assistant director of Tartu Observatory, said astrobiology was a modern emerging field of research and it is important for Estonia to be able to contribute to forefront science. Estonia’s participation in the European Space Agency’s research programme has helped create a new astrobiology research area at the University of Tartu.

Satellite Mission Control Centre at Tartu Observatory. Photo credit: Renee Altrov.

In ESA’s F-class mission, Comet Interceptor, Pajusalu is directing the development of an Estonian instrument, the OPIC (Optical Periscopic Imager for Comets), which is the first time Estonia has managed to fully partake in a deep-space mission. The goal of the mission is to intercept a comet that is entering the inner solar system for the very first time, potentially originating from another planetary system. Additionally, the ARIEL, (Atmospheric Remote-sensing Infrared Exoplanet Large-survey) includes stellar physicians Anna Aret and Mihkel Kama as members of the research group. Both missions are scheduled to launch in 2028.

These are the first science missions where Estonia gets a chance to present the country’s space research and technology. Until these missions, Estonia’s full participation in such missions was hampered by the large development times and monetary contributions and therefore participation was only possible through the teams of other ESA member states.

Cover: A man looking at the stars in Soomaa National Park in Estonia. The image is illustrative. Photo by Sven Zacek.

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