Earth Similarity Index

Tranquil life on MarsEver since the discovery of Mars over 4000 years ago, people have been mesmerized with the idea of taking off from Earth, landing on another celestial object, shaking hands with aliens, and settling in for the long haul. Nowhere is this more apparent in the human population than in the astronomer community, especially among those in SETI (Search for Extraterrestrial Intelligence). This community had a theory, that planets (or moons) similar to ours have higher chances of harboring life. They deduced that the habitable planets should have a similar size, density, gravity, and temperature as ours. These parameters together form a number for the Earth Similarity Index (ESI). The closer to 1 this number is, the more similar the planet is to Earth. In addition to looking at ESI, reference is also made to the planet’s distance from Earth. Our current spacecraft is nowhere near advanced enough to travel far into interstellar space. Even Voyager 1 has only traveled 0.002 light-years after cruising for 38 years.

ESI ChartAll these detailed figures won’t need to be studied in detail if only our neighboring planet Mars was already habitable. It only takes 2 years and 9 months for a roundtrip (19-month stay included), not 11.9 light-years one-way to the nearest possibly-habitable exoplanet Tau Ceti e. Unfortunately, Mars’s gravity is only 37.6% of ours, temperature ranges from -225 to 95*F (-143 to 35*C), and atmosphere not only is poisonous but isn’t thick enough to burn off incoming meteors.

Tau Ceti eAll though Mars may be inhospitable to Earth-like lifeforms, does that mean there won’t be any life at all? Probably not. Scientists have already discovered flowing water and they have yet to look at the sub-surface of the red planet. And scientists should start thinking outside the box, keeping an open mind as to which objects are in fact lifeforms. Aliens may be watching our every move through climatic anomalies.

Mammatus clouds or aliens?


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