If you spent too much time on the internet all the  way back in 2023, you may have seen a particularly   mind-blowing fact go viral: that sharks are  older than Polaris, A.

K. A., the North Star.

And it certainly is mind-blowing, but  probably not the way you’re thinking. Because while sharks are super old,  that viral claim may only be half true. Sharks may, in fact, be older than  just part of the North Star. [♪ INTRO] There are a few lines of evidence that point  to just how long sharks have existed on Earth.

First there’s the record. Fossilized  shark teeth and whole skeletons have been   found in rocks that date as far back as the  Devonian period, over 380 million years ago. And some fossilized scales may be  closer to 450 million years old.

But scientists can also estimate how long sharks  have been around by looking at modern species. By comparing the DNA of modern sharks  to their close relatives like rays,   they can estimate when the two  diverged, evolutionarily speaking. And ultimately, the picture all this paints is of  a group of animals that is, yes, very very old.

Sharks as a group have survived five mass  extinction events, and they’re older than   dinosaurs, trees, the Rocky Mountains, the  Atlantic Ocean …And, yes, Polaris, the North Star. ... Kind of. But to explain what I mean, I need to  pivot from paleontology to astronomy.

Polaris is a sorta-bright star  that hangs in the sky close to   the Earth’s North Pole as part  of the constellation Ursa Minor. Since the Earth wobbles a bit in space,  the star that’s closest to true north   rotates over time. But for the past  500 years or so, it's been Polaris.

And despite the title “The North Star”, Polaris is  actually a trinary system made up of three stars. Two of them, Polaris Aa and Polaris Ab,   are so close together we didn’t confirm  they were separate stars until 2006. So they’re collectively known as Polaris A.

And then there’s the third wheel  a bit farther away, Polaris B. But it’s Polaris Aa that really holds  the spotlight. Or…is the spotlight.

It’s by far the brightest of the lot, and  is what’s known as a Cepheid Variable star,   which means it switches between getting  brighter and dimmer like clockwork. But that’s not the really weird thing  about this system. The weird thing is that it seems like the stars in Polaris A  and Polaris B are wildly different ages.

According to some studies, Polaris A, or  at least the cepheid variable Aa, might be   around 75 million years old. Meanwhile, Polaris B  looks like it’s a whopping 2.1 billion years old. One is much younger than the very first  sharks.

The other is much, much older. But they’re supposed to be stellar siblings. If  you met three people who all claimed to be sisters   but two of them were toddlers and the other looked  like they’re pushing 90, you’d have questions.

And scientists do too. But they’ve  run into a couple of hiccups. The biggest, of course, is trying to pin  down the age of something that’s very,   very far away.

Which you may  have noticed most stars are. Astronomers have figured out  some fancy tricks, though,   like how a star’s brightness relates to its age. But to figure out how bright a star really is as  opposed to how bright it looks in the night sky,   you’ve got to know exactly how far away it is.

And here’s where our data on the  Polaris trinary comes up short. Our distance measurements  to the current North Star are simply not consistent from survey to survey. We think it’s about 320 to 520 light years away,  but that’s a pretty wide range of uncertainty.

Part of the problem might be that Polaris  A is too darn bright for some of our best   telescope tech that’s dedicated  to calculating stellar distances. For example, the Gaia mission was able to  estimate the distance to Polaris B was around   447 lightyears from us. But Polaris  A was too bright for Gaia to study.

Of course, you could just assume that  the Polaris A stars are basically the same distance from Earth as Polaris B. After all,  they’re supposed to be part of the same trinary. So that’s what one team of astronomers  did in their paper published back in 2018.

And when they plugged that assumed  distance into their models,   they got an age of Polaris Aa that  was 55 to 65 million years old. Unfortunately, another study from 2018 pointed  out that if you hold to that assumption,   you also get the result that Polaris B is about 30  times older than its cepheid variable companion. But don’t think astronomers haven’t tried  other techniques to resolve this, even if it’s not to prove that sharks are indeed  older than the entire North Star trinary.

For example, instead of basing it off  brightness, one group tried to start with   the stars’ masses based on photographs  of how they move around each other. But the age gap has stuck around. Which means astronomers still have  several hypotheses to work with.

Option one: nearly everyone has been  very wrong for a long time about Polaris   A and B being in the same system. While  that’s technically possible, it appears   unlikely given all the coincidences  that would have to come together. So option two is the stellar version  of a May December Romance.

The age gap between Polaris A and B is real and they  really are together, and it’s because   they started out as two separate systems and  then somehow found each other in deep space. Sharks would have been around at the time, but  it’s safe to say they wouldn’t have noticed. And there is option three that at least one of  the Polaris stars might not be what they seem.

Polaris Aa could actually be the  remnant of a recent stellar merger,   which would make it look a lot brighter  and younger than it otherwise should be. Combine that with the uncertain distance  from Earth, and you might be able to   calculate a new age that’s closer to Polaris  B, making all of Polaris older than sharks. But on the other hand, Polaris B could be  the one faking its brightness.

Maybe it’s actually another binary we haven’t  been able to get a good picture of. And that would make the whole system a  four-star system instead of a three-star one. Or, it could be Polaris B that’s the result of two stars smushing together.

It’s not impossible to test that hypothesis,   but that peskily bright variable star next  door will make any investigation challenging. And finally, there’s option four: there’s just  something really weird out there that we don’t know about yet,  or we’ve gotten something wrong  in our knowledge about how stars live and die. Which is simultaneously a boring answer,  and the one that’s most exciting.

Because who doesn’t love rewriting the  astrophysics textbooks? I personally keep a fine Sharpie on hand at  all times for that very purpose. But whether or not any part of the  North Star is truly younger than sharks,   there are plenty of other stars that definitely  are.

Many are even visible to the naked eye. Like the brightest star in the night sky,   Sirius A, is around 200 million years old.  That’s only about half as old as sharks. And then there’s that infamous  when-are-you-going-to-explode-already   Betelgeuse, which is just 10 million years old.

But perhaps the most mind-blowing fact  of all is that there are stars forming right now…    which means there’s at least  one out there that’s younger than you. But before I leave you to pontificate  about all the stars in the universe   younger than your whole self, I have  to show off our spiffy new merch! Each month for 2024, we’re releasing  a limited edition pin celebrating   some of the awesome things you’ll find in  outer space.

And…at least for January… the awesomeness of sharks in relation to the  awesome things you’ll find in outer space. But now that I think about it…Technically  the Earth is in outer space, so from a certain point of view, sharks are too! You can pick one of these up by  heading over to DFTBA.com/SciShow.

And from all of us here at  SciShow, thanks for watching. [♪ OUTRO]