Earth from Apollo 17 NASA photo
The Earth will be habitable for another 1.75 billion years. NASA

And now for some good news: A new astronomical model predicts that the Earth will be habitable for another 1.75 billion years. The researchers arrived at this number by calculating Earth’s distance from the sun to determine when the planet will exit the “habitable zone” and no longer be able to sustain liquid water.

The habitable zone, or “Goldilocks zone,” is the area around a star where liquid water could be sustained on a planet. Researchers from the University of East Anglia estimated the Earth will exit the habitable zone around the sun between 1.75 billion to 3.25 billion years, at which point the Earth will get closer to the sun, causing a dramatic increase in temperatures that will evaporate the oceans. The study was published in the journal Astrobiology.

According to lead researcher Andrew Rushby, from the university’s school of environmental sciences, “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. We estimate that Earth will cease to be habitable somewhere between 1.75 and 3.25 billion years from now.”

Rushby, however, also warns that climate change and other factors could lead to a “catastrophic and terminal extinction event for all life” much sooner than their estimates. “Humans would be in trouble with even a small increase in temperature, and near the end only microbes in niche environments would be able to endure the heat,” said Rushby in a statement.

Understanding the habitable lifetime, as the researchers put it, for a planet can lead to new insights on the development of complex, or intelligent life, on exoplanets, planets outside of the solar system. Astronomers have discovered 974 exoplanets to date, with NASA’s Kepler mission discovering 262 planets that could potentially support life. Rushby said humans have been around for a mere 200,000 years, whereas the first insects were on Earth nearly 400 million years ago.

A planet needs a relatively long habitable lifetime in order for life to develop. Calculating how long a planet will be habitable could eliminate some planets in the search for life or add others to the list. “Looking at habitability metrics is useful because it allows us to investigate the potential for other planets to host life, and understand the stage that life may be at elsewhere in the galaxy,” said Rushby.

The model used by the researchers is different as it focused on the habitable zone, and the time a planet is within that zone, which allows for comparisons with other planets. Kepler 22b and Gliese 581d, two planets that were compared to Earth, have incredibly long habitable lifetimes. Kepler 22b was discovered in 2011 and is described as the “first planet in habitable zone of a sun-like star” discovered by Kepler and Gilese 581d is a Super-Earth in Gilese 581’s habitable zone.

Kepler 22b has a habitable lifetime of 4.3 billion to 6.1 billion years while Gilese 581d has a habitable lifetime 10 times that. Rushby said, “Even more surprising is Gliese 581d, which has a massive habitable lifetime of between 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!”

With Earth exiting the sun’s habitable zone in a little under 2 billion years, Rushby said Mars may prove to be a viable option for future space colonists. The Red Planet will be in the sun’s habitable for 6 billion years, which could give Earthlings a new lease on life.