Astro2110 – The Solar System

Many scientists have theorized that we are not alone in the universe. Indeed, there are many scenarios that should lend themselves to the existence of life. The conditions inherent in theoretical models that have been developed to explain Earth’s formation and subsequent development of life exist elsewhere. Not only do they exist, but they appear in relative abundance.

Even within our own solar system, there exist several Jovian moons that harbor conditions that could be conducive to extremophile life. The methane rivers of Titan and the potential subsurface oceans of three of Jupiter’s moons: Europa, Ganymede, and Callisto, harbor conditions that could very well allow life to thrive.

Outside of our solar system, scientists have detected 200 “terrestrial” exoplanets (explain what this means) and 1,691 “Super Earth” exoplanets. Extrapolated observations from the Kepler space telescope indicated that there may be as many as 40 billion Earth-sized planets in a companion star’s habitable zone.

But we have yet to find any life outside of Earth. We have searched vigorously; but we have found absolutely nothing. Why? 1938 Physics Nobel laureate Enrico Fermi supposedly posed such a question in 1950 in casual conversation with some of his physicist friends. Ever since, the apparent contradiction between the absolute lack of observed advanced extraterrestrial life and the ample conditions for its existence have borne Fermi’s name as the Fermi paradox.

If the only life that exists elsewhere is archetypically similar to that on Earth (meaning that it is also composed of DNA, responds to environmental stimuli, reproduces, and so on) then other worlds resemble Earth in crucial aspects (such as mass, density, atmospheric composition, etc.) should be those that harbor life. If we are looking at only Earth-like worlds, we can frame the Fermi paradox as a competition between two theories: the mediocrity principle and the Rare Earth hypothesis.

The mediocrity principle suggests that life on Earth is not particularly special and that the chemical elements that make up life, and even the complex combination of features that make Earth habitable, are highly unlikely to have occurred only once, especially in our vast cosmic plane. Adherents to this theory include physicist Stephen Hawking, who said that “the human race is just a chemical scum on a moderate size planet, orbiting round a very average star in the outer suburb of one among a billion galaxies.”

Opposing this theory is the Rare Earth hypothesis, which argues that Earth’s situation is the result of an incredible number of improbable coincidences that are prerequisites for the formation of life. Both the mediocrity principle and Rare Earth hypothesis serve as “answers” to the Fermi paradox, but whether or not you believe them is based upon your understanding of human understanding and your belief in the expansion of our knowledge’s horizons.

Both approaches have their respective flaws. The mediocrity principle confidently asserts the existence of completely unverified life elsewhere on a self-admittedly incomplete body of evidence. On the other hand, the Rare Earth hypothesis restricts its predictive capacity by limiting itself only to the highly specific conditions which formed itself, possibly discounting a large number of otherwise habitable planets which could potentially harbor extraterrestrial life.

But ultimately, there exists only one solution to the Fermi paradox. We either find extraterrestrial life, or we die trying.