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  • [♪ INTRO]

  • In 2003, astronomers discovered an exoplanet named PSR 1620-26 b.

  • It doesn't have a fancy name, and it's likely just another gas giant,

  • this time, at about two times the mass of Jupiter.

  • It probably even formed like all other exoplanets out there.

  • But for scientists, this planet is anything but normal.

  • Even fifteen years after its discovery, researchers believe it's still the

  • oldest confirmed planet we've ever found.

  • Evidence suggests that it's 12.7 billion years old,

  • barely a billion years younger than the universe itself.

  • And that had a lot to teach us about planetary formation.

  • Although this planet wasn't discovered until the 2000s, its story,

  • at least in human history, really started in the 1980s.

  • In 1988, researchers began studying an object in a neighborhood called Messier 4, or M4.

  • It's a globular cluster, a very dense group of stars, about 5500 light-years away.

  • M4 has more than 100,000 stars, but this time,

  • scientists were investigating a pulsar called PSR 1620-26.

  • Pulsars are the remnants of explosive supernovas.

  • They emit beams of radiation and spin really quickly, like super fast lighthouses.

  • And as that beam sweeps across Earth, we see the star flash at extremely regular intervals.

  • That's how the pulsars got their name.

  • Except, the timing of this pulsar's flashes wasn't quite so regular.

  • They were just a little bit off, and that suggested there was something orbiting the star,

  • its gravity tugging the pulsar a little this way and that and affecting those predictable signals.

  • So astronomers got to work.

  • And after multiple years of observation and a lot of math,

  • they were eventually able to identify not one, but two objects around the pulsar.

  • The first was a white dwarf, which formed out of a mid-sized star like the Sun.

  • It's estimated that M4 contains more than 40,000 white dwarfs, so this wasn't that unusual.

  • The second object, though, was a planet.

  • And that was a lot more unexpected.

  • See, by 2003, astronomers had started finding exoplanets all over the place,

  • and we'd even found a few orbiting another pulsar.

  • But no one had ever found a planet in a globular cluster,

  • and many scientists weren't sure it was even possible.

  • Gravitational interactions in places like M4 can rip baby planets apart,

  • and with tons of stuff flying around, there are lots of major impacts.

  • It's just not a great place for planets to form, except, this one managed to survive.

  • Today, it's actually still the only known planet we've seen in a globular cluster.

  • Somehow, though, that still wasn't the strangest thing about finding a planet in M4.

  • What was even weirder is that this neighborhood is really old, about 12.7 billion years old.

  • According to what we know about cluster formation,

  • that means the stars within this group are equally ancient.

  • And by extension, so are any planets around them.

  • Even now, we're still figuring out exactly how planets form, but the general consensus

  • says that they form out of the disk of matter that orbits a young star,

  • as the matter starts glomming together and kind of snowballing.

  • This is called the core accretion model.

  • This process is supposed to happen soon after a star is born,

  • so planets and their host stars have about the same age.

  • So since most of the stars in M4 are nearly 13 billion years old,

  • it follows that this pulsar planet is, too.

  • And that makes it likely the oldest planet ever discovered.

  • That's more than just another record, though.

  • It also has a lot to teach us about the early universe.

  • See, the thing about the core accretion model is that,

  • if you're going to form a planet by snowballing stuff,

  • you need to have a lot of heavy, diverse elements.

  • Even gas giants are more than your basic hydrogen and helium.

  • But it's not like those heavy elements have existed since the Big Bang.

  • Instead, it took millions of years for them to form.

  • They only began to exist as stars were born, fused lighter elements together,

  • and then spit out the heavier products when they died.

  • And that's why finding this pulsar planet was such a big deal.

  • It was the first piece of physical evidence announcing that, nearly 13 billion years ago,

  • there were enough heavy elements to start forming planets after all.

  • It confirmed something researchers had been thinking about for years,

  • and it also hinted that there could be other ancient worlds out there, too.

  • Since 2003, astronomers have found more old planets,

  • but none of them have been able to topple this record.

  • But from what we now know, they should be out there.

  • So we'll just have to keep looking.

  • Thanks for watching this episode of SciShow Space!

  • We love scouring the research for the weirdest, most surprising, and most awe-inspiring stuff

  • out there, but we'd love to hear what you want to learn about, too.

  • If you have a suggestion for future SciShow Space videos,

  • go ahead and leave them in the comments, and we'll look into it.

  • And as always, you can keep up with the latest videos

  • by going to youtube.com/scishowspace and subscribing.

  • [♪ OUTRO]

[♪ INTRO]

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