The human race has 1.75 billion years – and maybe a lot more – to find a new home, according to a new study on how long habitable conditions will last on Earth.
Researchers at the University of East Anglia
(UEA) in Britain looked at exoplanets – planets outside our solar system – to come up with their estimate of how long Earth will be in the Sun’s “habitable zone.” This is the distance from a planet’s star at which temperatures are conducive to having liquid water on the surface, and therefore life as we know it.
“We used stellar evolution models to estimate the end of a planet’s habitable lifetime by determining when it will no longer be in the habitable zone,” said Andrew Rushby, from UEA’s school of Environmental Sciences. “We estimate that Earth will cease to be habitable somewhere between 1.75 and 3.25 billion years from now. After this point, Earth will be in the ‘hot zone’ of the sun, with temperatures so high that the seas would evaporate. We would see a catastrophic and terminal extinction event for all life.”
The findings also shed light on the potential for intelligent life elsewhere in the universe. Almost 1,000 planets outside our solar system have been identified so far by astronomers.
“The amount of habitable time on a planet is very important because it tells us about the potential for the evolution of complex life – which is likely to require a longer period of habitable conditions,” said Rushby.
He added that while there were insects 400 million years ago, modern humans only evolved within the past 200,000 years.
“Of course, much of evolution is down to luck, so this isn’t concrete, but we know that complex, intelligent species like humans could not emerge after only a few million years, because it took us 75 per cent of the entire habitable lifetime of this planet to evolve. We think it will probably be a similar story elsewhere,” he said.
Rushby and his colleagues looked at one exoplanet, Kepler 22b, and estimated its habitable lifetime to be 4.3 to 6.1 billion years. Another, Gliese 581d, could have a habitable lifetime of 42.4 to 54.7 billion years.
“This planet may be warm and pleasant for 10 times the entire time that our solar system has existed,” said Rushby.
While no true Earth-like planet has been discovered, the researchers say it’s possible there may be one as close as 10 light-years away, which is very close in astronomical terms. Despite the proximity, getting to such a planet would take hundreds of thousands of years with existing technology.
The solution may be closer to home.
“If we ever needed to move to another planet, Mars is probably our best bet. It’s very close and will remain in the habitable zone until the end of the Sun’s lifetime - six billion years from now,” Rushby said.
The paper appears in the journal Astrobiology