Having previously explored our solar system for potential extraterrestrial life, this article ventures further into space.
For a long time, it was unclear whether our solar system was unique in hosting planets. Today, thousands of extrasolar planets have been discovered, although we mostly detect these indirectly by observing their effects on their surroundings. With an estimated 40 trillion stars (200 billion galaxies, each with about 200 billion stars) in the known universe, the number of planets is likely to continue growing.
The methods used to detect extrasolar planets and the fascinating discoveries made have been detailed in separate specials. Here, it’s important to note that many exoplanets were discovered because of changes in brightness observed when studying distant stars. These fluctuations could either be a natural part of a star’s life cycle or indicate the presence of a planet. Longer observations are required to determine the cause.
However, current observational methods typically detect only large, Jupiter-like planets. It is only with the next generation of telescopes, such as the Terrestrial Planet Finder, that discovering Earth-like planets will become more feasible.
Drake Equation
According to current research, planets in a solar system are quite common, as planets have even been sighted in very close binary star systems. This was once thought improbable, as the proximity of two stars was assumed to leave no material for planet formation. Since many stars in the universe are part of binary systems, it is now accepted that many of these could also host planets.
The potential for these planets to harbor life can be estimated using the Drake Equation, also known as the Greenbank Formula. Frank Drake, a co-founder of the SETI project, conducted the first search for extraterrestrial radio signals in 1960.
N = R* • f_h • f_p • n_e • f_l • f_i • f_c • L
N = Number of intelligent civilizations existing today
R* = Star formation rate in a galaxy
f_h = Fraction of stars with an ecosphere
f_p = Proportion of stars with a planetary system
n_e = Average number of planets per planetary system within the ecosphere
f_l = Number of planets that actually develop life
f_i = Fraction of planets where intelligent life emerges
f_c = Fraction of civilizations that develop advanced communication technologies
L = Average lifespan of these technically advanced civilizations
Panspermia Theory
The panspermia theory posits that life's basic building blocks originated in space and were distributed to viable planets by solar wind in the form of spores. Although it was long thought that these spores would not survive cosmic radiation, an accidental discovery proved otherwise. On April 20, 1967, Streptococcus mitis bacteria accidentally carried aboard the unmanned lunar probe Surveyor 3 survived inside a video camera. When Apollo 12 astronaut Pete Conrad retrieved the camera during a mission and brought it back to Earth, scientists found the bacteria still alive after 31 months.
Today, we understand that certain bacteria could survive millions of years under extreme conditions, as active bacterial spores have been isolated from amber even after 30 million years.
Silicon-Based Life
Life as we know it requires carbon and other heavy elements, which did not exist immediately after the universe's birth. Only after the first generation of stars exhausted their hydrogen supply could heavier elements form, later becoming part of the interstellar medium through supernova explosions.
However, life may not necessarily be carbon-based; it could also be silicon-based, potentially forming structures entirely different from our own.
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