New findings out of Uppsala University in Sweden suggest that Earth is an incredibly unique place – in fact, out of the 700 quintillion terrestrial planets in the universe, there may be nothing else like it.
Combining knowledge about terrestrial planets, habitable zones, the early universe and the laws of physics, astrophysicists created a computer model simulating the evolution of the universe after the big bang, recreating the last 13.8 billion years. Results showed that the universe has more than 700 quintillion terrestrial (rocky) planets and that pretty much all of them look nothing like Earth. [Scientists Say Extraterrestrials May All Be Extinct]
Using their model, researchers devised a conservative approach to judge the likelihood of a terrestrial planets ability to support, and more importantly sustain life, in order to try and quantify the possibility of another Earth out there.
In their calculations, they included only solar-mass stars and excluded low-mass M-dwarf stars, based on evidence that extreme ultraviolet flares typical of low-mass stars would stymie life. They also excluded Super-Earths (rocky planets larger than Earth) since the habitability of these larger worlds is still a matter of debate for many reasons.
The team also took into account other effects on habitability, like extinction events, such as supernovae, gamma-ray bursts, active galactic nuclei, cosmic rays and comet/ asteroid impacts.
Results showed that, of the 700 quintillion terrestrial planets in the universe, there’s likely only one truly Earth-like world around a solar-mass star in our observable universe.
Though the rarity of another Earth was somewhat unexpected, to be clear, the study doesn’t definitively shut down the possibility of intelligent life elsewhere in the universe. There are many uncertainties in a calculation like this because our knowledge of all the complex pieces is imperfect. It’s likely that an all-knowing simulation could yield many Earth-like planets capable of sustaining life, but we’re just not there yet in our understanding, and the results of this model illustrate that .
Subsequently, the researchers suggest some guidelines to further enhance the search for extraterrestrial intelligence (SETI).
Most previous efforts to search for intelligent life have been focused within the Milky Way. However, evidence suggests that SETI should focus on targets outside of our galaxy, at a redshift of no more than z = 1- 2; or between approximately 7 billion and 11 billion light-years-away.
“If the probability for the emergence of intelligent life is sufficiently small, we could well be the only advanced civilization in the Milky Way,” scientists explained.
“When factoring in habitability considerations, which will tend to further favour the low density environment in the low-redshift Universe, and the escalating difficulties in detecting signatures (either signals or signs of astroengineering) of intelligent lifeforms at large distances, it seems that the prospects of extragalactic SETI should peak at redshifts below z ≈ 1–2.”
Materials provided by Terrestrial Planets Across Space And Time.