Compared to the vastness of our universe, the Earth is the only known planet to harbor life. This small planet of an average solar system is located approximately half way from the center of our Milky Way galaxy that is made of more than 100 thousand million star systems. Our galaxy is a part of  the local group of galaxies which hold over 1 trillion star systems. A group of galaxies is called a cluster and a group of clusters is called a supercluster. Our solar system is a part of the Virgo cluster which is a part of the larger cluster called the Laniakea supercluster. With these astronomical numbers of star systems, there could be several planetary bodies that could meet the criteria of sustaining life. Yet that is just the cluster of  galaxies; if we go to the farthest reaches of our universe, there are about two trillion galaxies, each containing millions of planets that could harbor life. 

Exoplanets are any planet that orbits a star outside of our solar system. The first discovery of an Exoplanet was in January of 1992 when Aleksander Wolszczan and Dale Frail announced a discovery of two uninhabitable rocky planets orbiting a pulsar. Today with more powerful ground telescopes and space telescopes like the Giant Magellan Telescope and Hubble, we have been able to discover thousands of exoplanets beyond our solar system. Yet out of any of those exoplanets is life possible on one of them? Is there a possibility of life on some distant planets thousands of lightyears away?  The first approximation of finding another extraterrestrial life in our galaxy was given by Frank Drake’s equation, which approximated the number N of technically advanced civilizations in the Milky Way galaxy as a function of astronomical, biological, and psychological factors. 

To find exoplanets, astronomers use the earth as a blueprint in order to find other planets with Earth-like characteristics. Life on our earth requires sun, moderate temperatures, water, and certain elements like carbon, oxygen, and nitrogen. Liquid water is essential for life as we know it. Where we find liquid water we also find life. The Goldilocks Zone refers to the habitable zone around a star where the temperature is just right - not too hot and not too cold for liquid water to exist on a planet. If an exoplanet is not in the Goldilocks Zone, life on that planet would not be able to exist because the water, a basic requirement of life, would either evaporate or freeze. Size and mass of a star have immense importance as it determines the output heat and energy, which is essential to life on planets. Hotter stars will always have farther Goldilocks Zones and vice versa. The size of the sun also matters as it plays a major role in sustaining an environment, as the heat of the star will determine the optimal position of each of the planets. This is a major criterion for determining the eligibility of certain planets as, without a correct Goldilocks Zone, a planet can not be considered a possible harborer of life.

While the distance between the exoplanet and the sun is important, making sure that the exoplanet’s atmosphere is not poisonous plays a significant role in classifying a planet as habitable. Yet how do scientists even detect these atmospheric conditions, as the exoplanets are light years away? Through extensive research and photochemical, global climate, and atmospheric escape models, scientists are able to create accurate information about the exoplanets atmosphere. Photochemical models may allow scientists to determine the atmosphere of planets that are similarly distant from their sun as Earth is from its sun. This is revolutionary, as without traveling lightyears away from Earth, we can possibly model atmospheres for distant planets. More importantly, it helps scientists eliminate planets that are not habitable or planets that couldn't sustain carbon based life. But what about other types of life, like methane-based or even nitrogen-based life? It is possible that life on other planets have evolved to conform to their atmosphere and the resources available on the exoplanet. 

Space telescopes such as James Webb (to be launched in 2021), Hubble, TESS, and Kepler travel our galaxy endlessly taking pictures of distant planets, and exploring new and exotic worlds. Hubble has contributed over 1.3 million observations to science like new pictures of Pluto and finding one of the largest exoplanets (Fomalhaut b), which is about three times the size of Jupiter. Similarly Kepler has discovered a solar system  consisting of six planets and a yellow dwarf star (G-type main-sequence star), about 2,000 lightyears away from Earth, and comparable in size to Uranus and Neptune.  Overall, it has  discovered over 2,600 planets outside of our solar system, and between 2 and 12 planets that are roughly Earth’s size and in the habitable zone of their star. Over its 9 years in space it showed scientists that there were more planets in our galaxy than stars. This discovery is significant because it shows how there are many possible planets that could harbor life, and opens our eyes to a more diverse universe. 

Why is finding life on an exoplanet so important to human civilization? Why do we continue to search for life if we know that is extremely unlikely ? As per the new calculations done using Drake’s equation, civilizations developing on a habitable planet are less than about one in 10 billion trillion, or one part in 10 to the 22nd power. But again there are more than 100 billion trillion stars in the observable universe. Finding life anywhere else in this vast universe is the holy grail of science. Any detection of extraterrestrial life will give humanity new insights into our place in the universe. It would benefit the human race as a whole, as if our planets start to die, or our sun expands to an enormous size, the distant planet would then become our last safe haven.