Sometimes to learn about something close to us, we have to look far away. This is the case with the Sun as it is very hard to determine its history and predict its future with only 400 years of telescopic observations. To answer some of those outstanding questions, astronomers look for other stars that are nearly identical to our own, which are called solar twins.
Recently two solar twins were found; one younger and one older. The younger is just 2.9 billion years old, while the older is 8.6 billion years old, compared to the Sun's age of 4.6 billion years. That is still young enough that it has not exhausted its hydrogen fuel and expanded as it started fusing helium. However, its chemistry has changed in a way astrophysicists are keenly interested in.
Measurements of the Sun reveal that it has less lithium than some models suggest, but this older solar-twin has even less. The younger solar-twin though has considerably more lithium, so this suggests that, by some mechanism, lithium is burned away as stars age. Interestingly, the chemistry of the older star is also similar to the Sun's in such a way as to suggest it may have formed rocky planets, similar to Earth.
Source: European Southern Observatory