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Four and a half billion years ago, the Sun pulled itself together from gas collapsing inside a giant, molecular cloud, but it didn't do it alone.
It was born in a star cluster where somewhere between 1000 and 10,000 other stars formed all at the same time and from the same cloud.

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Which means our favorite star may have thousands of solar siblings, many of them probably just like it elsewhere in the galaxy. 
The trouble is, we're not sure where they are.

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Most star clusters break apart after less than a 100 million years, scattering their stars far and wide, and many astronomers are interested in finding our solar siblings. 

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Because we still don't know why exactly life was able to develop here on Earth, but if something about the Solar System's birth environment helped for life to take hold, then those properties could be shared by our star's fellow litter mates. 
And astronomers have a few tricks up their sleeves that may help our star connect with the rest of its brood. 

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For one thing, every star has a particular chemical fingerprint or a tag, a specific pattern in its spectrum that tells us how much iron there is relative to hydrogen, or how much of other elements like aluminum or carbon there is relative to iron.

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And the stars that formed from the same cloud are expected to have the same basic fingerprint, but the abundance of some elements can change over the lifetime of a star, so not every element is useful in fingerprinting stars. 
Recently, a group led by Ivan Ramirez at the University of Texas, Austin found that the abundances of sodium, aluminum, vanadium, yttrium and barium all formed distinct patterns in stars, and their abundances don't seem to change during stars' lifetimes.

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So, other stars that have the same relative abundance of those elements as the Sun could be possible solar siblings. 
But there's a lot of stars out there, so just having matching chemical fingerprints isn't enough.
To be considered a true solar sibling, a star also has to be the same age as the Sun. 

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And the age of an isolated star is actually really tricky to measure, so usually our age estimates have a big margin of error. 
Then, a solar sibling star should also have the same dynamic origin as the Sun, meaning that if you traced the orbits of the two stars backward, it would put them in the same place at the same time when they were very young.

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Putting all these criteria together, Ramirez's team recently found one star that seems to meet all of these criteria. 
It has the same chemical fingerprint, it's about 4,5 billion years old and it would have been close enough to the Sun over four billion years ago that they could have come from the same star cluster.

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That star, probably the first of our rediscovered solar siblings, is called HD162826.
It's a little bit bigger than the Sun, about 1.15 times as much mass, and today it's around a 110 light-years away, toward the constellation Hercules. 

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Unless you're in really dark skies and have amazing vision, it's too faint to be seen with the naked eye, but it's a roughly sun-sized star that's reasonably close, so astronomers have been keeping an eye on it to see if it has planets.

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So far, this is the only star that matches all of the criteria of a long lost solar sibling, but there could be more than a thousand others out there. We're just waiting to find them.
And when we do, we will be eager to find out if there's anyone around those solar sibling stars, waving back. 

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