Earth’s days are numbered. Not on a timescale that matters to any of us, but numbered all the same. In a few billion years, the sun will begin expanding into a red giant. Its supply of hydrogen at its core depleted. The oceans will boil away, and the atmosphere will burn up. Our home will take Mercury’s place as the closest planet to the sun.
Sucks for those still around, huh? Hopefully, the human race is colonizing the stars long before the sun’s expanding size becomes a problem. But if we’re still stuck on Earth, our solar system could give us a second chance.
“Long after our own plain yellow sun expands to become a red giant and turns Earth into a sizzling hot wasteland, there are still regions in our own solar system – and other solar systems as well – where life might thrive,” says Kaltenegger.
Here’s how the solar system and the habitable zone line up today.
You can see being in the habitable zone doesn’t mean life is a given. Mars is a desolate, dry world.
Now, let’s take another look at our solar system about 8 billion years into the future.
Image credits: Cornell University
“When a star ages and brightens, the habitable zone moves outward and you’re basically giving a second wind to a planetary system,” said Ramirez.
In this scenario, the intriguing moons of Europa and Enceladus comfortably sit in the habitable zone. While frozen today, these worlds could see temperatures closer to those we see on Earth. The icy shell hiding the apparent Enceladus ocean would melt away.
Expanding our search for exoplanets and life
The search for life outside our solar system focuses on the familiar. Stars like the sun. Planets like Earth. And it makes sense. Obviously, we know life is on Earth – so why not look for places just like it? But the new research shows red giants should also be considered. And stars of all ages.
The possible second chance won’t last forever. It’s all dependent on the mass of the original star. “For stars that are like our sun, but older, such thawed planets cold stay warm up to half a billion years. That’s no small amount of time,” said Ramirez.
Smaller stars fare even better. Planets and their moons could rest in these habitable zones for up to 9 billion years.
“In the far future, such worlds could become habitable around small red suns for billions of years, maybe even starting life, just like Earth. That makes me very optimistic for the chances for life in the long run,” said Kaltenegger.
Worlds that are frozen solid today could one day get their shot at life. We won’t be around to see it happen in our solar system, but it does open up how we search for other potentially habitable planets. Until we find another habitable planet somewhere else, we really don’t have a template for life on other worlds. And until we do, we shouldn’t limit our search.