[♩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]
