Will we know if TRAPPIST-1e is alive?

Currently, the search for extrasolar planets is undergoing a dramatic transformation. With the deployment of the Kepler space telescope and the Transiting Exoplanet Survey Satellite (TESS), scientists have discovered thousands of exoplanets, most of which were detected and confirmed through indirect methods.

But in recent years, with the launch of the James Webb Space Telescope (JWST), the field has turned to one of characterization. In this process, scientists rely on the emission spectra of exoplanet atmospheres to search for chemical signatures associated with life (biosignatures).

However, there is some debate about which characteristics scientists should look for. Essentially, astrobiology uses life on Earth as a template when looking for signs of extraterrestrial life, just as exoplanet hunters use Earth as a measure of “habitability.”

But as many scientists point out, life on Earth and its natural environment have evolved considerably over time.In a recently published paper arXiv On a preprint server, an international team shows how astrobiologists can search for life on TRAPPIST-1e based on conditions that existed on Earth billions of years ago.

The team consists of astronomers and astrobiologists from the Global Systems Institute, the Departments of Physics and Astronomy, Mathematics and Statistics and the Department of Natural Sciences at the University of Exeter. They were joined by researchers from Victoria University’s School of Earth and Ocean Sciences and the Natural History Museum in London.

The paper describing their findings, “Biosignatures of preoxyphotosynthetic life on TRAPPIST-1e,” will be published in Royal Astronomical Society monthly notices.

The TRAPPIST-1 system has been in the spotlight since astronomers confirmed the existence of three exoplanets in 2016, rising to seven the following year. As one of many systems with low-mass, cooler M-type (red dwarf) parent stars, there are still open questions about whether its planets are habitable. Much of this involves the volatile and unstable nature of red dwarfs, which are prone to flare activity and may not produce enough of the necessary photons to drive photosynthesis.

With so many rocky planets discovered orbiting red dwarfs, including the closest exoplanet to our solar system (Proxima Centauri b), many astronomers believe these systems would be ideal places to search for alien life. At the same time, they also emphasized that these planets need thick atmospheres, inherent magnetic fields, adequate heat transfer mechanisms, or all of the above. Determining whether exoplanets possess these prerequisites for life is something that JWST and other next-generation telescopes, such as the European Southern Observatory’s proposed Extremely Large Telescope (ELT), hope to achieve.

But even with these and other next-generation instruments, there remains the question of what biosignatures we should be looking for. As mentioned earlier, our planet, its atmosphere, and all life as we know it have changed dramatically over the past 4 billion years. During the Archean Eon (approximately 4 to 2.5 billion years ago), Earth’s atmosphere consisted mainly of carbon dioxide, methane, and volcanic gases, with only anaerobic microorganisms present. It was only in the last 1.62 billion years that the first multicellular life emerged and evolved to its current level of complexity.

Furthermore, the number of evolutionary steps required to reach higher complexity (and their potential difficulty) means that many planets may never develop complex life. This is consistent with the Great Filter hypothesis, which states that while life may be common in the universe, advanced life may not be common. Therefore, simple microbial biospheres similar to those that existed during the Archean Eon are probably the most common. The key, then, is to conduct searches that isolate signatures of organisms consistent with primitive life and conditions common on Earth billions of years ago.

As Dr. Jake Eager-Nash, a postdoctoral researcher at the University of Victoria and lead author of the study, explained to Universe Today via email:

“I think Earth’s history provides many examples of what inhabited exoplanets might have looked like, and it’s important to understand biosignatures in the context of Earth’s history because we don’t have examples of what life looked like on other planets. In the Archean Eon During this period, when life is believed to first appear, there was a period of about a billion years before oxygen-producing photosynthesis evolved and became the dominant primary producer. Oxygen concentrations were indeed low, so if an inhabited planet Following a similar trajectory to Earth, then their oxygen concentrations would be very low. What that looks like is important.

In their study, the team created a model that took into account Archean-like conditions and how the presence of early life forms consumed some elements while adding others. This resulted in a model in which simple bacteria living in the ocean consume molecules such as hydrogen (H) or carbon monoxide (CO), producing carbohydrates as energy and methane (CH₄) as waste.They then considered how gases exchanged between the ocean and the atmosphere, resulting in lower H and CO concentrations and higher CH concentrations₄. Eagle Nash said:

“It’s thought that Archean-like biosignatures require the presence of methane, carbon dioxide and water vapor, and the absence of carbon monoxide. That’s because water vapor tells you there’s water, and an atmosphere that has both of those tells you there’s water.” Methane and carbon monoxide show that the atmosphere is in a state of imbalance, meaning that both substances should not be present in the atmosphere at the same time because atmospheric chemistry will convert all of one substance into the other unless something (like life) is sustaining it The absence of carbon monoxide in this imbalance is important because it is thought that life would have quickly evolved a way to consume this energy.

When gas concentrations are high in the atmosphere, the gases dissolve into the oceans, replenishing the hydrogen and carbon monoxide consumed by simple life forms. As the amount of methane produced by organisms in the ocean increases, it is released into the atmosphere, where additional chemical reactions occur and different gases are transported around the Earth. From this, the team obtained the overall composition of the atmosphere to predict which biological signatures could be detected.

“We found that carbon monoxide is likely to be present in the atmospheres of Archean-like planets orbiting M dwarfs,” Eagle-Nash said. “This is because the chemical reactions driven by the host star would be slower compared to planets orbiting the sun. Leads to higher concentrations of carbon monoxide, even if you have life consumed by this substance [compound]”.

For years, scientists have considered how to extend the circumsolar habitable zone (CHZ) to include Earth-like conditions from previous geological periods. Likewise, astrobiologists have been working on a broader study of the types of biological signatures associated with more ancient life forms, such as retinal photosynthetic organisms. In this latest study, Eagle-Nash and colleagues established a series of biosignatures (water, carbon monoxide, and methane) that could lead to discoveries on Archean rocky planets orbiting sun-like and red dwarf stars. life.