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  • [♩INTRO]

  • In 1849, we discovered an object between Mars and Jupiter called Hygiea.

  • For a while, we thought it was just another big asteroid in the asteroid belt,

  • but on Monday, a team announced in Nature Astronomy

  • that it might actually deserve a different title.

  • Based on their observations, Hygiea is probably a dwarf planet!

  • And it might also have a different origin story than once thought.

  • The requirements for being a dwarf planet are pretty simple:

  • You need to orbit only the Sun, be massive enough that your gravity pulls you

  • into a roughly spherical shape, and not be able to clear your orbit.

  • In other words, your gravity has to be weak enough that you can't push

  • similarly-sized objects out of your path.

  • As a relatively light object living in the asteroid belt,

  • Hygiea already checked two of these boxes.

  • But until now, we couldn't tell whether it was spherical, because we were busy

  • looking at other things, and because it's very dark and hard to see.

  • Then came this week's big announcement!

  • To make the new discovery, astronomers used the

  • European Southern Observatory's Very Large Telescope

  • to get the best images yet of Hygiea.

  • And we can now say for sure that it is really round!

  • That means it checks all the dwarf planet boxes!

  • Though, just to be clear, Hygiea isn't formally a dwarf planet yet

  • some official conversations will need to be had about it first.

  • But if it is reclassified, it will officially replace Ceres as the smallest dwarf planet

  • in our solar system.

  • So, this is all great; I mean, humans love categorizing things.

  • But these observations have greater significance for the solar system's history, too.

  • Because this team didn't just find that Hygiea is spherical.

  • They also noticed something weird about the object's surface.

  • Previous research has shown that Hygiea is the largest member in a family of

  • asteroids that all formed from the same parent body.

  • The working hypothesis has been that this parent body was hit

  • by a bunch of impacts that knocked off smaller asteroids until,

  • eventually, Hygiea was all that was left behind.

  • Based on this, Hygiea should be covered in big craters.

  • But the authors of this paper imaged 95% of the thing's surface,

  • and there are no giant craters to be found.

  • To solve this new mystery, the authors ran simulations to see what conditions could

  • have led to this scenario.

  • And they suggested the original parent body didn't survive all those impacts after all.

  • Instead, the impacts were likely so big that the parent body was totally destroyed!

  • Lots of the pieces just went flying off to form all of the smaller asteroids in the family,

  • but enough were big and close enough that they reformed into Hygiea!

  • So, keep an eye out for an official announcement,

  • and maybe we'll get to categorize Hygiea as a dwarf planet soon.

  • And speaking of big collisions

  • In 2017, scientists had the chance to directly observe something

  • amazing for the first time: the collision of two neutron stars.

  • Neutron stars are incredibly dense, neutron-rich objects,

  • and it's normally really hard to see what happens when they run into each other.

  • Partly because the events are pretty rare,

  • and partly because there aren't any neutron stars around here.

  • But we finally got a chance to do it when two stars collided

  • only 130 million light-years away.

  • Which in astronomy terms, is much closer than it sounds.

  • Last Wednesday in the journal Nature,

  • one team published their analysis of data from that collision.

  • And they found the best evidence yet of something we've suspected for a long time:

  • Neutron star collisions produce really, really heavy elements.

  • So, some context.

  • Stars form elements through nuclear fusion, which is pretty straightforward:

  • They fuse together lighter elements to create heavier ones.

  • At first, this process just involves turning hydrogen into helium.

  • But over a star's life, as more particles get smashed together,

  • it can make elements as heavy as iron.

  • But there are tons of heavier elements out there,

  • like copper and lead, that stars can't make.

  • The pressures and temperatures inside them just aren't high enough.

  • So to get these elements, you need something more.

  • Traditionally, scientists have believed these atoms come from supernovas:

  • hotter, more powerful explosions that happen when some stars die.

  • And that still seems to be true!

  • But according to this new paper, supernovas aren't the only events

  • that make heavy elements: Neutron star collisions can, too.

  • In the paper, the team found evidence that the collision was creating

  • the heavy element strontium - a lot of it.

  • In fact, about five Earth masses!

  • They suggest it came from a process called rapid neutron capture.

  • Essentially, that's where you have so many neutrons in one place that they just sort

  • of stick to the particles around them.

  • So you end up with a bunch of nice, heavy atoms.

  • If the atom is unstable, some of those neutrons

  • can break down into protons and electrons.

  • And that leads to heavier elements.

  • This is cool, because we need heavy elements to make things like planets.

  • So knowing that supernovas aren't the only creators out there

  • tells us something valuable about the makeup of the universe.

  • And another fun fact: This study officially confirms that neutron stars are actually

  • made of neutron-rich matter.

  • That was another case where we had a lot of math to support that assumption,

  • but no physical confirmation.

  • So, this work provides really clear, hard evidence

  • for two fundamental aspects of astrophysics.

  • You know, no big deal.

  • Thanks for watching this episode of SciShow Space News!

  • And an extra-special thanks to this episode's President of Space, Matthew Brant.

  • Matthew is one of our longtime patrons on Patreon

  • one of the people who supports SciShow

  • and helps us keep making content like this.

  • So, thanks for everything, Matthew!

  • SciShow is so much better because of patrons like you.

  • If you want to learn how to support the show

  • and become our next President of Space, you can go to patreon.com/scishow.

  • [♩OUTRO]

[♩INTRO]

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