The search for life beyond Earth It is one of the hottest topics in astronomy today. The curiosity to know if we are alone in the universe or not is something shared among human beings. With technological advances with more powerful telescopes and probes, the search has gained even more interest from both the public and the scientific community.
Of course, the basis for the search for life beyond Earth is our own planet and the evolution of life here. Exoplanets with an Earth-like atmosphere, composition, and environment are currently major research targets. This includes exoplanets that orbit stars similar to the Sun and are in the habitable zone of the respective star.
Fermi paradox: why haven’t we found extraterrestrial life yet?
An article recently sent to a scientific journal considers that The search for life must take into account other stages of planet Earth. The idea is to consider planets that have an environment similar to that of when the Earth was younger and with a greater amount of CO2, For example. This could give a direction of where life might be in the early stages.
exoplanets
The planets that are not in the Solar System called exoplanets. Currently more than 5,000 exoplanets have been observed and cataloged. The types of exoplanets differ from gas giants like Jupiter and Saturn until rocky planets like Earth and Mars. Depending on their size, they are called super-Earth, sub-Neptune and others.
Super-Earths are objects more massive than planet Earth but smaller than Neptune and Uranus with masses between 2 and 10 times the mass of Earth.
Observing exoplanets is not an easy task. One of the most used techniques is that of transients, which analyzes how much the star’s luminosity decreases as the exoplanet passes in front. For this it is necessary to observe the exact time and place. Another possibility is observe the gravitational interaction of stars with its planes and how the radial velocity changes.
TRAPPIST-1 System
The most famous exoplanet system is called TRAPPIST-1, discovered in 2016 with 3 exoplanets. Today, it is known that the system has a total of 7 exoplanets. It is located about 39 light years away and is composed of a central red dwarf star. The planets are named with the letters ba h.
Because it is a red dwarfthe habitable zone of TRAPPIST-1 is considerably different from the habitable zone of the Sun. Furthermore, a red dwarf has much lower emissions than the Sun and it may not be able to support photosynthesis on one of the planets. Another problem is the variability that red dwarfs have with the generation of more frequent flares.
Earth Evolution
The paper submitted to MNRAS suggests using different epochs from Earth’s past to compare with the environment of the exoplanet TRAPPIST-1e. The idea is to keep in mind that Life took a while to evolve and went through phases on Earth in which the environment was extrememainly during the last 4 billion years.
When analyzing times between 4 and 2 billion years ago, it is estimated that The Earth had a large amount of carbon dioxide and methane, as well as other gases present in volcanic eruptions. At that time simpler organisms existed and only in the last 2 billion years have they evolved into more complex organisms.
Biosignatures
Therefore, the idea would be to search biosignatures on planets that have Earth-like environments during a remote era. Biosignatures are indirect evidence of the presence of life on another star. There can be different types of biosignatures, the most common are chemical ones.
Chemical biosignatures are associated with presence of carbon in addition to oxygen and methane. Gases and molecules that are only produced in biological processes are also considered. Starting in 2022, the James Webb Telescope observes the spectrum of exoplanet atmospheres in search of biosignatures.
Comparison with TRAPPIST-1e
To compare them with observations of the exoplanet TRAPPIST-1e, the team of astronomers considered simple life forms in a phase of Earth where there would be an abundance of hydrogen and carbon monoxide. With this, it is possible to estimate what biosignatures would be observed in a scenario like this.
One of the results is that there would be an increase in methane (CH4) due to biological processes caused by these forms of life. CH4 could be a biosignature clue to look for in exoplanets that have environments similar to the one studied like TRAPPIST-1e.
Sources and references of the news:
Eager-Nash et al. 2024 Biosignatures from pre-oxygen photosynthesising life on TRAPPIST-1e arXiv.
