“Two possibilities exist: Either we are alone in the Universe or we are not. Both are equally terrifying” (Arthur C. Clarke)
Life on Earth is a common thing. Life on clouds and in water looks interesting. And life on places other than the Earth (extraterrestrial life) looks…ummmm…possible. In this article, I will try to note some information ranging from hypothesis to scientific information related to the life on places other than Earth.
The Drake Equation
In the year 1961, Frank Drake provided an equation to calculate the possible number of civilizations in our galaxy. The Drake equation is as follows:
N = R* • fp • ne • fl • fi • fc • L
N = The number of civilizations in The Milky Way Galaxy whose electromagnetic emissions can be observed.
R* = The rate of formation of stars appropriate for the production of intelligent life.
fp = The fraction of stars having planetary systems.
ne = The number of planets, within a solar system, having an environment appropriate for life.
fl = The fraction of suitable planets where life actually present.
fi = The fraction of life bearing planets where intelligent life emerges.
fc = The fraction of civilizations that develop a technology that releases observable signs of their existence into space.
L = The length of time such civilizations release detectable signals into space.
At this time, there are only rough estimates for all these variables. However, according to present estimates, there could be 7.8 billion life bearing planets, in which 13% of those habitable planet have chances of developing life and there are 100% chances that life develops intelligence. Moreover, there are more than 72,000 communicating civilizations in the galaxy and about 11,000,000 billion communicating civilizations in the universe (BBC Future, 2012).
Presence of water on other planets
Researchers are of opinion that water and oceans are most important things for the life on any planet. They have reported that oceans play a vital role in optimal climate stability as well as habitability. It is due to the presence of oceans that surface temperature changes moderately with seasonal changes and solar heating (University of East Anglia, 2014). Water has been reported on many planets, moons, and comets, but large bodies of liquid water have not been found on other astronomical bodies.
Habitable zone is that area around the star, where the life could be found on planets and moons. This area is not-too-close to the star and not-too-far from it. In this habitable zone, planets are considered to have the liquid water on their surface that is important for the known form of life. Presently, habitable zone is based on the absorption parameters of water and carbon dioxide obtained through ITRAN (high-resolution transmission molecular absorption) and HITEMP (high-temperature spectroscopic absorption parameters) (Moskowitz, 2013).
In our own solar system, habitable zone is present from 0.99 astronomical units (AU) to 1.7 AU. Here, AU refers to the distance between Earth and the sun. It is showing that our Earth is very close to the inner edge of the habitable zone. One of the most important planets found in the habitable zone is Gliese 581d (Moskowitz, 2013), which is about 7 times heavy as compared to the Earth and located about 20 light years away from us.
Among other potentially habitable planets are Kepler-438b, Gliese 667 Cc, Kepler-442b, Gliese 832 c, Kepler-62e, Kepler-283c, Kepler-436b, Kepler-296f, Gliese 163 c, HD 40307 g, Kepler-61b, Kepler-443, Kepler-22b, Kepler-440b, Kepler-439b, Kepler-298d, Kepler-62f, Kapteyn b, Kepler-174d, and Kepler-186f.
Mars as a probable candidate to support the life
In order to make Mars hospitable, we have to work on the atmosphere, atmospheric pressure, radiations coming from space, and the small size of Mars, among other important things.
According to our present knowledge, Mars has inhospitable surface for the life in the present form. However, scientists believe that we can change the environment of other planets to make it more hospitable – a process known as “terraforming” means “making similar to Earth” – and Mars can be one of those planets from where we can start our experiments of enabling the living organisms to live on other planets.
One of the most important problem in the process of terraforming is the lack of atmosphere. Mean pressure on the surface of the Earth is about 7 millibars – one thousandth of a bar, i.e. equal to a million dynes per square centimeter. However, Mars is not close to this atmospheric pressure. In this case, human beings would need a pressure suit to go on Mars. Atmosphere, in a minute amount, consists of about 95% CO2 that is harmful to human beings and animals, which live on oxygen. Though plants can utilize CO2 but they do need oxygen especially in the night time. Other components of atmosphere are about 2.7% nitrogen and 1.6% argon. Oxygen and water vapors are in very small amount. Radiation could be another major problem in making the planet hospitable (University of California, San Diego, n.d.).
Scientists are of opinion that heating the planet to evaporate CO2 and obtaining a good amount of gas from a theoretical reservoir could help in providing a sufficiently thick but breathable atmosphere. Moreover, some types of bacteria taken from Earth can also help in making the planet more hospitable by modifying the atmosphere. In this case, primitive cyanobacterium Chroococcidiopsis are considered as the best candidate in converting some of the CO2 to the utilizable oxygen. Acid-loving bacteria can also provide a good amount of help in this regard. In order to work on reduction of the harmful effects of radiation, plants can be engineered. These plants could help in providing a supportive environment. However, even after solving all these problems, a major problem remains and that is the small size of Mars that would not be able to hold favorable atmosphere for longer periods of time (University of California, San Diego, n.d.).
Chances of life on Europa
Europa is the smallest of the four largest moons of the planet Jupiter. This moon is the sixth largest moon of the solar system. It is considered as the brightest moon in the universe due to its smooth surface. Scientists are of opinion that an extra-terrestrial life could be found on Europa. This moon has gotten much attention of scientific studies. It has been thought that Europa might have liquid water and different sources of energy. Moreover, the warmer inside of Europa due to strong tidal heat could also help in having liquid water under the layers of ice. Europa’s density is showing that it could have a water ice that is partially in the form of liquid. This moon is thought to have oceans that could be as deep as 50 km or more (University of California, San Diego, n.d.).
Chances of life on Titan
Titan – one of the moons of Saturn – is also considered to have some form of life or atmospheric conditions that can support life. Its atmosphere is largely made up of nitrogen having less than 1% of methane. Its atmospheric surface pressure is more than that of Earth, but its temperature is very cold. Its atmosphere is found to have good amount of organic molecules in the form of products of the ammonia or methane. Hydrogen cyanide, a compound used in amino acids, is also a part of the atmospheric molecules. This is showing that some form of primitive life could be found there. However, reduced temperatures are decreasing the chances of the presence of known form of life (University of California, San Diego, n.d.).
Chances of life on Enceladus
Enceladus is the sixth largest moon of Saturn. The Cassini mission gave strong evidence that the moon has liquid water ocean with energy sources, nitrogen, organic molecules and inorganic salts (McKay, Anbar, Porco, & Tsou, 2014), along with minute quantities of simple hydrocarbons such as propane, methane, formaldehyde, and acetylene.
BBC Future (2012). Drake equation: How many alien civilizations exist? Retrieved from http://www.bbc.com/future/story/20120821-how-many-alien-worlds-exist
McKay, C., Anbar, A., Porco, C., & Tsou, P. (2014). Follow the Plume: The Habitability of Enceladus Astrobiology, 14 (4), 352-355 DOI: 10.1089/ast.2014.1158
Moskowitz, C. (2013). “Habitable Zone” for Alien Planets Redefined. Retrieved from http://www.scientificamerican.com/article/habitable-zone-redefined/
University of California, San Diego. (n.d.). Life in the Universe. Retrieved from http://earthguide.ucsd.edu/virtualmuseum/litu/litusyllabus.shtml
University of East Anglia. (2014). Oceans vital for possibility for alien life. ScienceDaily. Retrieved from www.sciencedaily.com/releases/2014/07/140720203459.htm