“It seems that the universe produces plentiful real estate for life that somehow resembles life on Earth.” ~ American cosmologist Erik Petigura
Life requires molecular structures which can metabolize to obtain energy, and which can retain information and use it for replication. Once that occurs, given a permissible environment, life arises and evolves.
“We used to think that the sort of chemistry that makes life could only happen on Earth. We were wrong.” ~ German biochemist Leonie Mueck
The chemical compounds and natural reactions that led to life on Earth are in no way unique. Complex organic molecules grew on the icy dust grains that lived in the infant solar system, warmed by ultraviolet photons.
Methanol (CH3OH) is a key substrate in the synthesis of organic molecules leading to life. In the right conditions, carbon monoxide (CO) on the surface of interstellar dust can react at low temperatures with hydrogen (H2) to create methanol.
The cold clouds that give birth to stars are a cradle for methanol production. From there, a variety of circumstances conspire to build complex organic molecules in space.
Meteorites contain many organic compounds, some so complex as to appear as a preserved extraterrestrial life form, like cyanobacteria.
“The traditional habitable zone is known as the Goldilocks zone. A planet needs to be not too close to its sun but also not too far away for liquid water to persist, rather than boiling or freezing, on the surface. But that theory fails to take into account life that can exist beneath a planet’s surface.” ~ British cosmologist Sean McMahon
The presumed habitable zone for planets in this solar system is between the orbits of Venus and Mars. Yet, as the life potential of Europa and Titan illustrate, a body’s composition and dynamics are more important than its orbital band.
The Saturn moon Enceladus has a crust of ice 5–35 km thick. Underneath is a toasty, mineral-rich saltwater ocean capable of hosting life. The gaseous mixture in geysers near Enceladus’ south pole suggests methane-releasing microbes.
The same may be said of Jupiter’s moons Callisto and Ganymede; Triton, a moon of Neptune; and Pluto. Underneath icy crusts are oceans warmed by radioactive decay in the core and kept liquid via trace amounts of ammonia. There is a universal abundance of water in which life may brew.
Archaea on Earth survive in conditions like those in Enceladus’ subsurface ocean and in other celestial bodies. There have been rich ecosystems of subsurface Earth microbes for billions of years.
“So much of life is within the Earth rather than on top of it.” ~ American microbiologist Karen Lloyd
There are over 640 billion planets in the Milky Way. Over 20% – 130 billion – may have a habitable surface. Many more likely harbor life within.
As the Milky Way illustrates, a single galaxy is vast: beyond imagination in scale. Earth illustrates the wide tolerance of conditions in which life can exist. Given the ease with which the molecular building blocks of life come together, it is inconceivable that Earth alone supports life.
The Catholic Church burned Italian Dominican friar Giordano Bruno at the stake in 1600 for suggesting the possibility of “a plurality of worlds.” Today’s clergy are more inclined to hedge their bets, figuring that “brother extraterrestrial would still be part of creation.”
“If it’s true that our species is alone in the universe, then I’d have to say the universe aimed rather low and settled for very little.” ~ American comedian George Carlin