The universe contains somewhere in the vicinity of 100 billion galaxies and if we threw it a birthday party, there would be around 13.8 billion candles to blow out. That's a lot of space and time for life to evolve in the universe. The Earth has only been around for 4.5 billion of those years, however, so it seems there's a fair chance that much older lifeforms than ours are out there somewhere. That may not be the case according to a new study out of the Harvard-Smithsonian Center for Astrophysics, which suggests that, from a cosmic perspective, we may have arrived before our time.
"If you ask, 'When is life most likely to emerge?' you might naively say, 'Now,'" says lead author Avi Loeb of the Harvard-Smithsonian Center for Astrophysics. "But we find that the chance of life grows much higher in the distant future."
Loeb and his team set out to determine the likelihood of "life as we know it" evolving between two time periods – approximately 30 million years after the Big Bang, when life first became possible thanks to the first stars seeding the cosmos with elements such as carbon and oxygen, and 10 trillion years from now, when scientists believe the last stars will flicker away and life will die.
To do this, they looked at the factor most connected to life – the lifetimes of stars. The higher a star's mass, the shorter its lifetime and the lower the likelihood that life will evolve. Conversely, the smallest stars will burn bright for trillions of years due to the fact that they burn nuclear fuel more slowly, thus providing increased opportunity for the evolution of life.
After crunching some numbers comparing star size to the likelihood of life development on surrounding habitable planets, the team found that life is most likely to develop in the future and on the common smaller red dwarf stars. These stars are set to drastically increase in numbers in the future, meaning the potential for life will continue to grow – the chances of life are 1,000 times higher in the distant future than now.
"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. Another possibility is that the environment around a low-mass star is hazardous to life."
These hazards include ultraviolet radiation and strong flares during their youth, which would evaporate the atmospheres of any planets in their habitable zone.
As was also suggested by this NASA and Space Telescope Science Institute study, the conclusion is that the majority of Earth-like worlds that could potentially evolve over the life of the universe don't yet exist. We could simply be searching too soon.
Still, potentially habitable exoplanets are being uncovered at an accelerating pace, and the continuing search for habitable planets around red dwarf stars in particular – a search that is soon to be given a boost by the James Webb Space Telescope – will shed more light on the question of whether life on Earth is premature in a cosmic sense.
Loeb, who is also currently the chair of the advisory committee for the star-chasing initiative Breakthrough Starshot, believes that it's likely that primitive forms of life exist around other stars. "I am agnostic about intelligent life, but believe we simply have to search for it."
The findings have been accepted for publication in the Journal of Cosmology and Astroparticle Physics.
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