Natural panspermia explains alien life
The belief that life is able to naturally spread throughout the Solar System and Galaxy
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Is it know that there is life on Earth that is able to survive in the harshness of space.It is also know that matter can be transferred not only between planets, but also between solar systems. It's possible that if some of these asteroids had life on/inside them, and they then impacted another planet, life could potentially thrive on this planet.
Similarly to the Accidental Artificial Panspermia argument, it is known that on earth there are extremely tough organisms known as Extremophiles. This includes the Tersicoccus Phoenicis, which has been found in NASA's clean rooms, and the Tardigrade which has been demonstrated to be able to survive in the vacuum of space for at least 10 days. On Earth, meteorites from Mars and Mercury as well as many other planetary bodies have been found, and it is presumed this process also occurs in the other direction. This tells us that matter can and is frequently transferred between the planets, usually due to a large impactor ejecting it from its homeworld. On October 2017, Astronomers also for the first time observed asteroid Oumuamua, the first known interstellar object to enter our solar system. It was found to have a tough coating a few meters thick that could shield the core from solar radiation. If, over the billions of years that the universe has existed either an asteroid within a solar system, or an interstellar object had some form of life on it, it is possible it could transfer it to another planet where it could survive. It is possible that not only is this how life arrived at earth, but life could have also escaped earth using this technique. Helping to seed other planets in the Solar System and Universe.
Tersicoccus Phoenicis has demonstrated the ability to survive the harshness of space directly. Tardigrades have only demonstrated the ability to be able to travel moderately extreme conditions and only for periods on the scale of days and months. Interstellar objects could be travelling for billions of years. Asteroids within our solar system would be travelling at a minimum for months, likely years, centuries or millennia.
It has been demonstrated that life can survive the hard conditions of space for a limited time. It has been observed that matter is frequently transferred between both the planets within our solar system and between our system and others with the discovery of the interstellar asteroid Oumuamua. If a comparable lifeform to the extremophiles seen on Earth was onboard one of these objects travelling through space, it is possible it could be used to seed another planet.
Rejecting the premises
This limited time that they can survive is only on the scale of days, any longer and the survival rate dramatically decreases. Only one object has been observed travelling between solar systems. Though it may be more common, the only evidence we have points to it being an extremely rare event. None of this supposed lifeforms have been found yet, so while they may exist, it is completely hypothetical.