The famous astronomer Carl Sagan once said that the question of the nature of life on Earth, and the question of whether life can be found beyond Earth, are two sides of the same question. In the case of Panspermia, both questions are answered succinctly.
Life exists beyond Earth, and life as we know it on our green-blue planet came from outside our atmosphere. Several celestial objects have been suggested as the source of life on Earth by supporters of the Panspermia theory. This includes Mars, comets and asteroids, and even other star systems.
Early ideas on Panspermia
Panspermia is a very old idea, dating back at least to the time of the ancient Greeks. Some of the earliest proponents of this scientific hypothesis in modern times include astronomers Fred Hojl and Chandra Vikramasing. Although no evidence has been found for this hypothesis of the origin of life, the discoveries of the last century make Panspermia more plausible.
These discoveries include intriguing evidence that life may once have existed on Mars. One line that has given more credibility to this thesis is the fact that the earliest indisputable evidence of life in the geological record dates to about 3.8 billion years ago, near the end of the Late Heavy Bombardment (LHB), a period of great activity in the early solar system, where the rate of collisions between planetary bodies was much higher than it is today.
Did life come to Earth from Mars?
In 1984, a meteorite was discovered in the Alan Hills region of Antarctica. It was called ALH84001, and for a decade it was forgotten. But in 1994, geochemical and microscopic analysis showed that the object was a Martian meteorite and very unusual from others.
The scientists found that it contained complex organic molecules known as polycyclic aromatic hydrocarbons (PAHs), which are often associated with microbial activity. They also found magnetite mixed with iron sulfide. Usually these 2 minerals usually do not want to be together in the presence of carbonates, in case they are not produced by living organisms.
In addition, the researchers discovered some rod-shaped nanostructures with an unusual appearance, which bore similarities to some types of bacteria. These three discoveries inside the meteorite were considered by some scientists as possible proof of life on the red planet.
But over the years, much of the evidence that initially seemed intriguing is now considered questionable, and the hypothesis of a non-biological origin is currently more favored.
The question of whether or not life exists on Mars will be answered by a mission that is planned to launch in the early 2030s. Meanwhile, data continues to be collected that shows that Mars was once a cleaner and wetter planet, and that there may have been life in the distant geological past
Life from comets or asteroids?
Chandra Vikramasing, an astronomer and mathematician at the University of Buckingham, Britain, thinks that life is likely to have formed in the interior of comets. He says the trillions of cometary objects likely to exist in the solar system offer far more possibilities where life could have formed than in early Earth environments.
According to him, it is possible that a comet was "infected" with life when it passed through the upper atmosphere of a planet rich in life. This could allow life to implant in a comet without forming in it. Of course, this does not explain how that life was formed. It just pushes the problem further back in time, and onto another planetary body.
Another promising site for a non-planetary origin of life may be asteroids. They are rocky bodies found mostly between the orbits of Mars and Jupiter. Most asteroids are probably fragments of protoplanetary bodies that may have been the size of Vesta, about 530 kilometers in diameter.
Many asteroids are rich in organic matter, including amino acids. Additionally, isotopic analysis of asteroids shows that some asteroids have deuterium-to-hydrogen isotope ratios similar to water on Earth, making it more likely that asteroids contributed material to Earth during its formation.
Life from other star systems?
At first, scientists were very skeptical that microbes inside small rocks could survive the great distances between stars, especially after an interstellar journey.
it would take hundreds of millions or billions of years. But this opinion has changed with the recent discovery of 2 interstellar objects that have passed through our solar system.
The first was Oumuamua, which in the Hawaiian language means "the first messenger from afar." It was discovered in 2017 by astronomers using a University of Hawaii telescope.
The second object was discovered in 2019. 2I/Borisov, was very similar to the comets of our solar system, except for its hyperbolic orbit.
2I/Borisov and Oumuamua were discovered only within 2 years of each other. And it suggests that visits from interstellar objects are more common than previously thought. This has made scientists more open to the possibility that life travels not only between planets within a solar system, but also between solar systems.
The future of Panspermia theory
There is currently no strong evidence that life has formed on other planets. But with every astrobiological discovery, it becomes more likely that life will soon be discovered beyond Earth. The question that can be asked is: Will this life be completely different from any life we have experienced, or lives that will turn out to be our lost interplanetary or interstellar "cousins"? The only way to find out is to keep exploring.
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