For millennia, humans have been wondering what lies in the vast expanse of the sky that is filled with stars only visible at night. This curiosity led to the development of 'astrobiology.' This field of study, formerly known as exobiology, encompasses the search for the origin of life beyond Earth, along with understanding its future scope. This interdisciplinary subject combines knowledge from various other scientific fields, such as geology, biology, astrology, oceanography, atmospheric science, and aeronautical engineering.
One of the pioneers in astrobiology, Joshua Lederberg, a molecular biologist, was reaching out to colleagues hinting that there may be life in space waiting to be discovered, even before the National Aeronautics and Space Administration (NASA) was established formally Since then, numerous astrobiologists have been interested in the vast outer space filled with dust, gas, charged particles from stars, radiation from the Big Bang, electric and magnetic fields, etc. [5]
Apollo 14 Astronaut Alan B. Shepard Jr. assembles equipment on the lunar surface in February 1971. Image source: https://solarsystem.nasa.gov/system/news_items/main_images/820_as14-68-9405_1600.jpg
Life, as we know it on Earth, is a product of mainly six elements, namely carbon, nitrogen, sulphur, hydrogen, oxygen, and phosphorus. At different temperatures and atmospheric pressures, these six elements, in different combinations, formed the earliest and basic forms of life on Earth, such as the structures of RNA and DNA. Based on NASA’s studies in 2011 on the 12 meteorites found in Antarctica, there may be proof of the components of DNA and RNA, such as adenine, cytosine, etc., being formed in outer space. [6]
The subject of biochemistry would be non-existent without understanding the important role of water as a medium for various chemical reactions. Water is almost a mandate in the formation of organic compounds. It acts as a solvent, enabling the formation of compounds that are precursors to life and that were eventually incorporated into asteroids in the early solar system. Reactions like photosynthesis, hydrolysis, and catabolism - all use water as a medium. These compounds have enabled us to get more insight into the concept of "life" in outer space and on Earth. [1]
There have been several ground-breaking and astonishing discoveries in the field of astrobiology, like when thermal models and tectonic evidence were used to conclude the possible existence of an ocean stretching to almost 100 kilometres beneath Pluto’s surface. Moreover, as evidenced by satellite images, there is water flowing on Mars as one reads this article. Although the water is briny, it still is a fantastic discovery. [7]
In 2013, the small exoplanet Kepler-37b, a planet slightly bigger than the Earth's moon, was discovered about 215 light-years away from us. Though the planet was at first thought to host life, it was later discovered to be far too hot. At around the same time, astronomists discovered Kepler-78b. Being about 80% bigger and 20% wider than our own planet and with a density similar to that of the Earth, the planet lies 400 light-years away from us and completes an orbit around its star in 8.5 hours. Sadly, this planet is also far too hot to host life as temperatures on it can reach approximately 2,000 degrees Celsius (3,680 Fahrenheit). [8]
Comparison of Kepler-37b size with the Earth’s Moon and Mercury
Image source: https://www.exocast.org/exocast-15b/
Scientists at NASA have conducted a series of experiments in 2015, suspending the test bacteria Deinococcus radiodurans out of Japan's Kibo Lab on the International Space Station using a robotic arm. Throughout the three-year duration of the experiment, the bacteria had no protection from cosmic ultraviolet rays, X-rays, or gamma-rays. Through the extensive studies conducted on extremophiles, it has been discovered that the bacteria can survive in space by carving small holes in rocks. The experiment results prove that D. radiodurans can survive in space for more than three years. Further research may prove that life could be transferred between planets via meteorites. The results of the experiment showed that the bacteria towards the outer layer of the cell mass died, but the cells on the inside of the mass survived, mainly because the dead cells shielded the inner mass from DNA damage. When the outer layer was thick enough, the inner cells survived for several years. [2]
D. radiodurans is a bacterial species that is remarkably resistant to radioactivity. While the human genome contains two copies of DNA, D. radiodurans contains more than ten copies of its genome, meaning that most of the copies are redundant but extremely useful. The extra copies of DNA in the bacteria efficiently code for proteins that repair damaged DNA through the deoxyribonucleic acid damage repair pathway [2].
A team of researchers led by Jane Greaves from Cardiff University, Wales, UK, announced the detection of phosphine in the cool deck clouds of Venus. Phosphine, mainly associated with the presence of aerobic bacteria, is a molecule consisting of three hydrogen atoms and one phosphorus atom. Phosphine is typically produced by members of the Enterobacteriaceae family; they produce acetic acid, which further promotes phosphine production. Though the discovery of a molecular footprint of a gas does not confirm the existence of life on Venus, it is still an astounding discovery. [3]
There is also widespread discussion on sending human beings to Mars. As enticing as that sounds, sending a spacecraft to Mars with all the resources needed to sustain a few people would be quite a tedious task. We have one idea to put that doubt to rest, growing plants on Mars! It does not sound easy, but we do have some hope that certain plants will flourish on the planet. The planet's surface is rich in iron, mainly iron oxides, and due to the absence of an ozone layer, more ultraviolet radiation reaches the surface. Through the ‘Red Thumbs Mars Garden Program’, students at Villanova University, Pennsylvania, USA, obtained simulated Martian soil and planted lettuce, kale, potatoes, garlic, and hops. To their surprise, some of the experimental plants, such as lettuce and kale, grew well in the Martian soil. Unlike the potatoes grown by Mark Whatney, the protagonist of Andy Weir’s ‘The Martian,’ the potatoes planted by the students did not grow well. The major challenge here is removing perchlorate from Martian soil by either rinsing the soil with water or by using perchlorate-eating bacteria. [4]
Students grew plants, including garlic, kale, sweet potatoes, hops, and lettuce. Villanova University, Pennsylvania, USA
Image from: https://skyandtelescope.org/astronomy-news/some-plants-grow-well-in-martian-soil/
Though not many institutes openly fund research in astrobiology, searching for life in space, for extreme environments on Earth where life can exist, and for planets like Earth will always continue. There is little chance that we might find life forms like us in space, but we might find environments that support human colonization or bacterial life to flourish. There are many associated hindrances, the major one being the exposure to radiation while travelling to Mars. This poses a threat of undue mutations to plants and humans alike. The availability of water, toxic soil, and freezing cold temperatures pose further risks to the program. This possibility makes limited but devoted people venture into this field. Though we have just begun to explore space, future discoveries made with advancements in the field may lead to the world made familiar to us by sci-fi movies.
References
[1] Mottl, M.J., Glazer, B.T., Kaiser, R.I. and Meech, K.J. (2007). Water and astrobiology. Geochemistry, 67(4), pp.253–282.
[2] Levy, M.G. (2020). Scientists Discover Exposed Bacteria Can Survive in Space for Years. [online] Smithsonian Magazine. Available at: https://www.smithsonianmag.com/science-nature/scientists-discover-exposed-bacteria-can-survive-space-years-180975660/ [Accessed: 9 January 2022].
[3] Jenkins, R & Morris, T & Craig, P & Ritchie, Alisdair & Ostah, N. (2000). Phosphine generation by mixed- and monoseptic-cultures of anaerobic bacteria. The Science of the total environment. 250. 73-81. 10.1016/S0048-9697(00)00368-5.
[4] Carlisle, C. (2018). Some Plants Grow Well in Martian Soil. [online] Sky & Telescope. Available at: https://skyandtelescope.org/astronomy-news/some-plants-grow-well-in-martian-soil/ [Accessed: 9 January 2022].
[5] Kaufman, M. (2012). NASA Astrobiology. [online] Nasa.gov. Available at: https://astrobiology.nasa.gov/about/history-of-astrobiology/ [Accessed: 8 February 2022].
[6] Brown, D. and Neal-Jones, N. (2011). NASA - NASA Research Shows DNA Building Blocks Can Be Made in Space. [online] www.nasa.gov. Available at: https://www.nasa.gov/home/hqnews/2011/aug/HQ_11-263_Meteorites_DNA.html [Accessed: 8 February 2022].
[7] Klotz, I. (2016). Underground ocean found on Pluto, likely slushy with ice. Reuters. [online] 16 Nov. Available at: https://www.reuters.com/article/us-space-pluto-idUSKBN13B2F7 [Accessed: 16 February 2022].
[8] Francis, M. (2013). Tiny exoplanet is smaller than Mercury (and probably hotter, too). [online] Ars Technica. Available at: https://arstechnica.com/science/2013/02/tiny-exoplanet-is-smaller-than-mercury-and-probably-hotter-too/ [Accessed: 16 February 2022].
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