Notes on interstellar hitchhikers and the origins of life.
By the time we realized that there was an extrasolar intruder, ‘Oumuamua, named after the Hawaiian word for “scout,” had already passed its closest point to the Sun and was leaving, as fast and stealthily as it had arrived. We are talking about the first sighting, in 2017, of an asteroid from another area of the galaxy, a messenger from distant worlds.
On timescales of the order of millions or tens of millions of years, fragments like ‘Oumuamua can bring different star systems into contact. Finally, we should remember that it takes the solar system about 220 million years to revolve around the center of the galaxy. Since it formed 4.5 billion years ago, it has made the full circuit about 20 times. This means that, in the timescale in which life emerged on Earth, the newborn solar system made at least three complete circuits, coming into contact with fragments from distant star systems.
We know of various living species that can endure extremely hostile conditions such as those in space: a nearly perfect vacuum, extreme temperatures, and ionizing radiation. In addition, the tardigrade’s DNA is protected by a protein that reduces radiation damage. Is this information enough to make us assume that these micro-animals come from space? I would say no. Their unusual metabolism is more likely the result of evolutionary adaptation that happened on our planet. In fact, tardigrades are among the very few living beings that have emerged unscathed from all five extinction events that have occurred on Earth.
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