Life Beyond Earth
- Oct 17, 2022
- 4 min read
In order to discuss the potential of life existing beyond Earth, we must first define parameters suitable for a habitable planet. A habitable planet is simply a planet that is able to harbor and maintain life. In order for a planet to be described as habitable though, there are specific criteria that it must meet. In order to define this criteria, Earth is often used as an example because it is the only place in the Universe, as of now, that we know of that supports life. Thus, some key requirements include the planet's size, the atmosphere, and the distance from its host star. The planet must be large enough to contain liquid water, because its gravitational pull will prevent the water molecules from flying off into space. In addition, a planet must have an atmosphere, to ensure that water is kept mostly in its liquid form- otherwise it would be inaccessible for life to use in its solid or gas form. Lastly, the planet must be located at the right distance from the star to ensure that water can exist in its liquid form; if a planet is too close to its star, then the water will evaporate, but if the planet is too far from its star, then it will freeze. This distance is often referred to as the habitable zone or the Goldilocks zone. It is important to note, though, that just because a planet is located here does not guarantee that it is habitable; for example, Venus is located in the habitable zone, yet it contains too many greenhouse gases, which renders it incapable of hosting life. Furthermore, it is also important to note that these criteria may only be the tip of the iceberg when looking for life beyond Earth. For example, Earth hosts a number of extremophiles, which is life that is able to exist in the most extreme conditions, such as the deepest parts of the Earth's oceans. Thus, it is very possible for extremophiles to exist in other parts of the Universe, in which it may not even require water or oxygen to survive.
Europa
As we learned in the Moons in the Solar System Pt. 2 blog, Europa is one of Jupiter’s many moons. But what makes this moon even more interesting is the fact that it may have the potential to host life; scientists believe this because there is evidence to believe that Europa has an ocean full of water beneath its icy crust. For example, data from the Voyagers spacecraft during their flybys show that the surface of Europa may have been active “at some time in the past”, due to icy material that “appeared to have flowed into [the][...] gaps” of cracks (NASA, 2021). Furthermore, Europa’s surface has a lack of impact craters, “which are expected to build up over time” as planetary objects are “constantly bombarded by meteorites”; this may suggest that something may have covered them, such as “icy, volcanic flows” (NASA, 2021). To add onto the evidence, “patterns of fractures” in the icy surface of Europa have been found, which have led scientists to conclude that tidal forces may be at play (NASA, 2021). Thus, NASA’s Europa Clipper, a mission that is expected to launch October 10th, 2024, will “seek to confirm the presence of [Europa’s][...] ocean” by conducting measurements of the impacts of the tides (NASA, 2021).
Enceladus
Similar to Europa, Enceladus is also believed to have a subsurface ocean, due to the fact that it spews water vapor through cracks in its icy surface. Something interesting about Enceladus, in particular, is the fact that the Cassini spacecraft made detections of methane, which can be a sign of life, as well as other “hydrogen and organic molecules”, as it flew through one of the water vapor plumes (Earthsky, 2021). Thus, scientists theorize that Enceladus’s subsurface ocean may contain hydrothermal vents, which may act as a heat source for life. To add to this theory, Earth also has hydrothermal vents of its own, in which life near them is able to use a process known as chemosynthesis (we encourage you to do more research on this phenomena) to survive and thrive. If life on Earth is able to survive without sunlight near hydrothermal vents, what stops life from doing the same on Enceladus?
Titan
Just as with Enceladus, the Cassini spacecraft also made a detection of a subsurface liquid ocean on Titan by using “numerous gravity measurements” (NASA, 2021). Furthermore, ESA’s Huygens probe also provided strong evidence to further suggest the possibility of a subsurface ocean through the measurement of radio signals. Thus, Titan has the potential to harbor life similar to ours in its subsurface ocean, as well as life different from ours on its surface, due to the presence of rivers and lakes of liquid methane.
Thank you for reaching the end of this blog. Be sure to check out our Moons of the Solar System blog series and our CBSS series on Instagram for more information on each dwarf planet mentioned! Don't forget to like and share and stay tuned for our next blog post. And as always, keep gazing skywards!
Bibliography
Marshall, M. (2021, October 12). Here's why scientists don't know how life on Earth began. How did life on Earth
begin? | BBC Science Focus Magazine. Retrieved October 12, 2022, from https://www.sciencefocus.com/science/how-did-life-on-earth-begin/
Methane on enceladus: A possible sign of life? EarthSky. (2021, June 18). Retrieved October 10, 2022, from
https://earthsky.org/space/methane-on-enceladus-methanogens/
NASA. (2021, February 4). Titan - in depth. NASA. Retrieved October 11, 2022, from
https://solarsystem.nasa.gov/moons/saturn-moons/titan/in-depth/
NASA. (2021, June 8). Evidence for an Ocean. NASA. Retrieved October 10, 2022, from
https://europa.nasa.gov/why-europa/evidence-for-an-ocean/
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