Will Earth still exist in 5 billion years?

L2 puppis
CC BY 2.0 L2 Puppis in the early stages of forming a butterfly-like planetary nebula. (ESO/P. Kervella)

Astronomers look to another star and its orbiting planet for a sneak peek of own solar system when the sun becomes 100 times larger than it is now.

Given that we have yet to create a good working model of a crystal ball or time machine, sometimes the best we can do is look to our older relatives to get a sense of how we might end up. Astronomers are kind of doing the same thing, albeit on a slightly more cosmological scale.

Using the most powerful radio telescope in the world, an international team of astronomers are peering into the life of the star L2 Puppis – a “nearby” red giant star that five billion years ago was much like the sun is today.

"We discovered that L2 Puppis is about 10 billion years old," says Ward Homan from the KU Leuven Institute of Astronomy. "Five billion years ago, the star was an almost perfect twin of our Sun as it is today, with the same mass. One third of this mass was lost during the evolution of the star. The same will happen with our Sun in the very distant future."

Remarkably, in their observations the scientists discovered an object orbiting the giant star – likely a planet, and one that could offer clues to the fate of our own orb.

L2 is a mere 208 light years away from Earth – which to astronomers means pretty close. The team used the ALMA radio telescope for their soothsaying, a doozy of instrumentation in Chile comprised of 66 individual radio antennas that work together to form a giant virtual telescope with a 16-kilometre diameter.

ALMA© ALMA, the world's largest observatory, on the high-altitude plateau of Chajnantor in the Atacama desert in Chile. (ALMA/ESO/NAOJ/NRAO))

What they have observed portends of an interesting future of our own big star and subsequently, the heavenly body that we call home.

"Five billion years from now, the Sun will have grown into a red giant star, more than a hundred times larger than its current size," says Professor Leen Decin from the KU Leuven Institute of Astronomy. "It will also experience an intense mass loss through a very strong stellar wind. The end product of its evolution, 7 billion years from now, will be a tiny white dwarf star. This will be about the size of the Earth, but much heavier: one teaspoon of white dwarf material weighs about 5 tons."

The outlook for Mercury and Venus, for example, isn’t so rosy. They will be engulfed in the giant star and quickly dismissed. As for Earth, the jury is still out.

"The fate of the Earth is still uncertain," says Decin. "We already know that our Sun will be bigger and brighter, so that it will probably destroy any form of life on our planet. But will the Earth's rocky core survive the red giant phase and continue orbiting the white dwarf?"

So what we do know is that Earth will likely not support life as we know it – whether or not the planet can survive the epic whims of the sun is anyone’s guess at this point. But further understanding of the relationship of L2 Puppis and its planet promises to deliver a clearer picture. And given the lack of crystal ball, we’ll have to rely on ALMA for glimpses into our very distant future.

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