In astrobiology, a core methodology used is “The Great Analogy”. The only known instance of life to man in the universe is based on one pale blue dot – planet Earth. Scientists use the knowledge about our origins and numerous life forms to predict how life could be formed on other planets.
In other cases, astrobiologists seek to understand extraterrestrials by searching for them. As the final part of this series, we will explore the role of extremophiles in astrobiology and the Search for Extraterrestrial Intelligence (SETI)!
The Ultimate Survivors in Nature – It isn’t pretty.
There is a variety of organisms on Earth that somehow have optimal growth in extreme conditions, or environments deemed too challenging for carbon-based life forms to survive known as extremophiles. Sure, they aren’t the nicest-looking organisms, but they can live in incredibly high temperatures and saline or acidic places. Due to their unique abilities, they are the most abundant life form to exist and have been dated back to 40 million years ago. These organisms have pushed the boundaries of life and have been used to answer the question: can life survive in space?
There are numerous types of extremophiles, including:
Psychrophiles: Can adapt to cold habitats like the poles and high mountain altitudes
Thermophiles and hyperthermophiles: Able to thrive at high temperatures, such as volcanoes, desert hot springs, and hydrothermal vents
Acidophiles: Grows at pH levels less than 5 and are often found in acid-mine drainage sites and acidic lakes
Alkaliphiles: The opposite of acidophiles; grow at high pH levels, like in sodic environments
Piezophiles: Thrives at highly pressurized conditions deep under the ocean
Halophiles: Flourishes in places with high salinity, e.g. sea, salt lakes, and brine pools
Xerophiles: Grows in dry climate/low water availability
Oligotrophic microbes: Require little nutrients to survive
Radioresistant microbes: Can endure high radiation
Metallophiles: Prefers to grow in high metals/heavy metals concentrations
NASA and other space companies have tried sending microorganisms and other extremophiles to conduct in-situ experiments, where they are exposed to radiation and the real space vacuum. After months of investigation, they found that many extremophiles could endure and grow in space, redefining the limit as to where life could exist.
The properties of these extremophiles can be attributed to a range of adaptations that have evolved via natural selection. Some have proteins and enzymes that can operate even under extreme conditions, as opposed to those typically found in the human body, while others may have modified microbial membrane properties like proton permeability and lipid structure/composition. In addition, there may also have been horizontal gene transfers of plasmids, integrons, and bacteriophages which results in changes in the genome.
Astrobiologists are constantly studying the wide array of environments within our solar system, and with the study of extremophiles, they can analyze which ones can or cannot support life. Much research is done on the extremophiles that live in analog environments which are conditions that mimic those found in other planets or moons, because this can provide insight on not only whether life is possible but also the mechanisms of its survival and help identify possible biosignatures to be used in future missions.
An interesting example of this is Europa, one of the more famous Jupiter’s moons. Europa has a 100km long ocean, which is approximately three times the size of Earth’s and has a crust made of ice. Similar to Earth, Europa also has tides created by the strong gravitational pull of Jupiter. Their tides are much stronger and more dynamic, constantly moving the crust. Europa has some of the peak conditions for life; the large body of water may contain organic molecules, and the movement of the tides can maybe – just maybe – bring the exact molecules together at the right time, in the right conditions. Thanks to extremophiles, we now know the high salinity and cold temperatures of the ocean are no longer a limiting factor, and there might already be life existing in Europa’s oceans.
In a study, the chemistry of water deep below the Earth’s surface was analyzed and revealed evidence of endoliths (organisms that can survive deep within the Earth’s crust and solid rock). Moreover, an absence of sulfur indicated the possibility of sulfate-metabolizing bacteria there. This is an example where extremophiles could inhabit an environment of radioactive rocks, use them as food and oxidants, and be completely independent of oxygen. This type of condition is analogous to the subsurface rocks Europa.
Another well-developed area of study is the (poly)extremophile models in Martian environments. Bacillus spores have been found to survive arid conditions, high radiation levels, large temperature fluctuations, real space vacuum conditions, high perchlorate salt concentrations, and also regoliths (a layer of unconsolidated loose material e.g. dust, soil, broken ricks covering solid rock) that mimics Martian soil geochemical composition. Debaryomyces hansenii, a halotolerant yeast, is the most perchlorate-tolerant microbe found thus far, making it an important model for life on Mars due to its high perchlorate concentration, which prefers liquid water despite subzero temperatures. It can also further the understanding of the biochemistries of organisms existing in Mars’ brine pools.
Search for Extraterrestrial Intelligence (SETI)
This search has been going on for almost a century, with the first, albeit rudimentary, attempt done in the late 19th and early 20th centuries. It all started with Mars, and scientists including Nikola Tesla and Guglielmo Marconi believed that the power of electrical transmissions would allow us to communicate with Martians. On the 21st and 23rd of August 1924, Mars approached Earth, and a National Radio Silence Day in America was held in the hopes that they would receive contact with extraterrestrial life on Mars. Even an airship was flown with a huge radio receiver and cryptographer three kilometers above the Arizona Naval Observatory, in anticipation of a long-awaited message.
The first modern SETI experiment, Project Ozma, was completed by Frank Drake and Cornell University and used interstellar radio waves to study distant planetary systems. One of the arguably most significant milestones in SETI was the Wow! signal recorded on the 15th of August 1977. Jerry R. Ehman, an astronomer, was analyzing the data recorded by the ‘Big Ear’ radio telescope at Ohio State University. What he found was a simple string of data ‘6EQUJ5’ which represented an intensity variation over time. It is believed to have originated from the constellation Sagittarius and lasted for 72 seconds, the maximum period of observation by the Big Ear (limited by its fixed position and Earth’s orbit). Though no definitive result has come from this signal thereafter, it remains a likely record of extraterrestrial transmission.
The Search for Extraterrestrial Intelligence has developed much further since then, with new techniques and methods, like seeking technosignatures (the signals or large astroengineering structures that are inexplicable by nature). Technology is used as a proxy and an indication of a possibly intelligent technologist behind it. However, astrobiologists typically focus on biosignatures, as introduced in previous articles.
There is so much funding, technology, and talented astronomers going into SETI, and – perhaps – we will find evidence of life out there within the 21st century.
WATCH this interview with an astronomer to learn more about the field of astrobiology and the logistics and science that drives SETI.
Works Cited
Bailey, R. (2020). Extremophiles - Extreme Organisms. [online] ThoughtCo. Available at: https://www.thoughtco.com/extremophiles-extreme-organisms-373905 [Accessed 5 Feb. 2024].
Insane Curiosity (2021). What is Astrobiology Explained. YouTube. Available at: https://www.youtube.com/watch?v=VVqp0RjjRzg [Accessed 5 Feb. 2024].
Megaprojects (2021). SETI: The Search for Extraterrestrial Intelligence. YouTube. Available at: https://www.youtube.com/watch?v=UbD6mh3pdcM [Accessed 5 Feb. 2024].
NASAeClips (2018). Our World: Where Do We Find Extremophiles? YouTube. Available at: https://www.youtube.com/watch?v=iwvNbymAsJQ [Accessed 5 Feb. 2024].
Schultz, J., Alef dos Santos, Patel, N. and Alexandre Soares Rosado (2023). Life on the Edge: Bioprospecting Extremophiles for Astrobiology. Journal of the Indian Institute of Sciences, [online] 103(3), pp.721–737. doi:https://doi.org/10.1007/s41745-023-00382-9.
TEDx Talks (2017). Astrobiology: The Search for Life Beyond Earth | Marta Filipa Cortesão | TEDxUniversityOfPorto. YouTube. Available at: https://www.youtube.com/watch?v=K-N0_kMvtFU [Accessed 5 Feb. 2024].
WIRED (2019). Astronomer Explains How SETI Searches for Aliens | WIRED. YouTube. Available at: https://www.youtube.com/watch?v=UVlUy77d-MU [Accessed 5 Feb. 2024].
Wolf, J. (2016). Applications of Extremophiles in Martian Astrobiology. [online] University of Minnesota Digital Conservancy. Available at: https://hdl.handle.net/11299/195241 [Accessed 5 Feb. 2024].
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