One day, aliens may stumble on the charred remains of Earth and understand that we were here, ancient aliens they never got to meet. A team of scientists led by Professor Abraham Loeb has calculated that present-day life might actually be premature from a cosmic perspective.
The Universe is 13.8 billion years old, while our planet formed just 4.5 billion years ago. Due to the expansion of the Universe, its temperature is continuously decreasing, and is now slightly above the absolute zero point, at about -270 ° C. But there was a time, between 10 and 17 million years after the Big Bang, when the temperature was between 0 and 100 ° C, the temperature at which water can be liquid. In theory, this is the earliest period that life may have originated in the Universe, although it doesn't seem very likely because of the lack of heavy elements -elements heavier than helium- during that period.
More information: Born in the Universe: the panspermia theory
It wasn't until 30 million years after the Big Bang that life as we know it became possible, when the first stars seeded the cosmos with the necessary elements like carbon and oxygen. And in about 10 trillion years from now, after the last stars have faded away and died, the story will be over. Avi Loeb and his colleagues considered the relative likelihood of life between those two boundaries.
"The general idea that many people have is that, since we exist next to a star like the Sun in a galaxy like the Milky Way, for life to exist you need these conditions,” says Loeb. “But in fact, low-mass stars are much more common than the Sun. The sun isn’t a typical star. Red dwarfs are very long-lived; they can live 1,000 times longer."
Loeb explaines that stars with just three times the mass of our own sun will not live long enough to help create life on planet. On the other hand, stars with the lowest mass – weighing less than 10 percent of the sun – will live for 10 trillion years, with the chance of life occurring on their planets increasing over time. In fact, chances of life are 1000 times higher in the distant future than now.
However, the habitable zone around these small stars would be much closer in, so any planets might be more vulnerable to harmful radiation shooting off of the star. Especially in their early years, red dwarfs release massive flares and ultraviolet radiation that can strip planets in the habitable zone of their atmosphere. Even worse, the star's gravity could pull much harder on one side of the planet, causing more volcanic activity that could lead to runaway greenhouse effect and the oceans boiling off.
But Loeb maintains that those constraints don't preclude the search for life on smaller stars. A number of ways for life to form on those planets have been postulated, and there are so many exoplanets, at least 100 billion in the Milky Way, that some percentage might become the exception to any rule.
"So then you may ask, why aren't we living in the future next to a low-mass star?" says Loeb. "One possibility is we're premature." The same could apply to the famous Fermi Paradox – the conflict between the high probability of alien life and the lack of proof of any. The solution to this paradox might be that we simply happen to be one of the first.
Another possibility is that the environment around a low-mass star is hazardous to life. To determine which possibility is correct—our premature existence or the hazard of low-mass stars—Loeb, who wrote a chapter for a new book on the subject as well, recommends studying nearby red dwarf stars and their planets for signs of habitability. Future space missions like the Transiting Exoplanet Survey Satellite and James Webb Space Telescope should help to answer these questions.