A planet has been discovered around L2 Puppis, a red giant star 208 light-years from Earth. The star is just your average red giant, but it has something very special for us. It used to look a lot like our Sun.

An international team of astronomers has been studying this system by using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, and they believe this offers a unique view to the future of the Solar System and our planet in particular. The discovery was published in the journal Astronomy and Astrophysics.

“We discovered that L2 Puppis is about 10 billion years old,” Ward Homan, from the KU Leuven Institute of Astronomy in Belgium, said in a statement. “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.”

The planet orbits 300 million kilometers (186 million miles) from its star, which is twice the distance between Earth and the Sun. The planet itself is not a good model for Earth, being 12 times the mass of Jupiter, but the astronomers are curious about the interactions between the planet and its star.

“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,” said co-author Professor Leen Decin, also 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, seven 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 five tons.”

^{Annotated image with the ALMA observation. P. Kervella/CNRS / U. de Chile / Observatoire de Paris / LESIA}

The red giant Sun will be so bloated that it will easily expand almost to our own orbit, destroying Mercury and Venus in the process. But the impact that this phase will have on Earth remains in large part unclear.

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

The team will continue to study L2 Puppis, as the system might reveal something new about our own star.