Astronomers have discovered an 8.2-billion-year-old solar twin that offers a peek at how our Sun will look like in future.

A team led by astronomers in Brazil has used ESO’s Very Large Telescope to study the oldest solar twin known to date.

Located 250 light-years away, the star HIP 102152 is more like the Sun than any other solar twin — except that it is nearly four billion years older.

This older twin may be host to rocky planets and gives us an unprecedented chance to see how the Sun will look when it ages, researchers said.

“For decades, astronomers have been searching for solar twins in order to know our own life-giving Sun better. But very few have been found since the first one was discovered in 1997. We have now obtained superb-quality spectra from the VLT and can scrutinise solar twins with extreme precision, to answer the question of whether the Sun is special,” said Jorge Melendez (Universidade de Sao Paulo, Brazil), the leader of the team and co-author of the study.

The team studied two solar twins — one that was thought to be younger than the Sun (18 Scorpii) and one that was expected to be older (HIP 102152).

They found that HIP 102152 in the constellation of Capricornus (The Sea Goat) is the oldest solar twin known to date.

It is estimated to be 8.2 billion years old, compared to 4.6 billion years for our own Sun. On the other hand 18 Scorpii was confirmed to be younger than the Sun - about 2.9 billion years old.

Studying the ancient solar twin HIP 102152 allows scientists to predict what may happen to our own Sun when it reaches that age, and they have already made one significant discovery.

“One issue we wanted to address is whether or not the Sun is typical in composition. Most importantly, why does it have such a strangely low lithium content?” said Mr. Melendez.

Lithium was created in the Big Bang along with hydrogen and helium. Astronomers have pondered for years over why some stars appear to have less lithium than others.

With the new observations of HIP 102152, astronomers have taken a big step towards solving this mystery by pinning down a strong correlation between a Sun-like star’s age and its lithium content.

“We have found that HIP 102152 has very low levels of lithium. This demonstrates clearly for the first time that older solar twins do indeed have less lithium than our own Sun or younger solar twins. We can now be certain that stars somehow destroy their lithium as they age, and that the Sun’s lithium content appears to be normal for its age,” TalaWanda Monroe, the lead author of study said.

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