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As the largest planet in our solar system, Jupiter has had a major impact on things around here.
It's affected orbits, acquired moons, and generally shaped what our neighborhood looks like,
so it's no surprise that scientists are interested in learning more about it.
Lately, a big way they've been doing that is with the Juno spacecraft,
which has been studying Jupiter's interior since 2016.
It's doing this by being on the interior, which wouldn't be possible,
but by measuring Jupiter's gravitational tug, among other things.
And not long after it arrived, it sent us back some surprising data.
The data suggested that the planet's core is less dense than expected,
and last week in the journal Nature, one team proposed why.
Their evidence supports the idea that shortly after Jupiter formed,
it was struck by an object 10 times the mass of Earth;
one that, otherwise, may have become its own planet.
Before Juno arrived at Jupiter, many researchers thought the boundary between
the planet's heavy core and its lighter, surrounding material was pretty much distinct.
But now, that does not seem to be the case.
Instead, the boundary is fuzzy,
almost like the elements from the core are bleeding into that surrounding envelope.
The team behind this new paper hypothesized that this could have happened
if something big hit Jupiter early in its history.
That collision could have broken apart the planet's early core and mixed up its insides,
and things wouldn't have settled down even after billions of years.
Which would explain the results from Juno.
To test this hypothesis, the researchers ran a series of simulations
that took place during Jupiter's formation around 4.6 billion years ago.
This is also the time when the solar system was forming,
so the region was a lot more populated by rocky bodies trying to make planets.
The models suggested that Jupiter's formation would have gravitationally messed with these bodies,
and it would have put at least one of them onto a new orbit;
an orbit that would eventually smash Jupiter head-on.
To get the results we see today, this object would have to have been about 10 times the mass of Earth,
meaning it could have become a planet in its own right if it weren't for pesky Jupiter eatin' stuff up.
So, like, thanks, Jupiter! We coulda had another planet!
This all being said, the simulation only worked under certain conditions.
Like, if the baby planet grazed Jupiter instead of hitting it head-on,
or if Jupiter had a larger core and the impactor a smaller one,
the simulation didn't produce the same results.
That doesn't mean this new hypothesis is wrong,
but it does mean it's worth considering other options.
For example, the paper's authors suggest that
Jupiter's core could also be suffering from a kind of erosion.
Or maybe the planet swallowed smaller bodies that broke apart as they sank.
Scientists will need to analyze a lot more data before they can say anything definitive.
But this kind of research should help us better understand ways large planets can develop,
both in our solar system and around other stars.
When it comes to exoplanets, though, the large planets aren't the only ones we're interested in.
Astronomers are also on the hunt to find planets with sizes and orbits like Earth's.
Some of this is for general cataloging reasons, but also, we want to know if our planet is unique!
We want to know how many worlds are out there that,
at least in some ways, resemble our home.
But that's easier said than done.
Scientists usually find exoplanets that orbit their stars faster and much more closely than Earth does,
since that makes it easier for them to confirm their data.
So it's hard to estimate how many worlds like ours there are out there.
But that has not stopped researchers from trying!
Last week in The Astronomical Journal, one team published a paper
that tried to estimate how many of these Earth-like planets might exist.
And in the process, they proved just how tricky making these estimates is.
The team used data from the now-defunct Kepler mission,
which hunted for exoplanets by monitoring nearly 190,000 stars over four years.
This isn't the first time scientists have used Kepler data for something like this,
but this group argued that a lot of previous work hasn't taken into account the data's biases.
Basically, because it's easier to find planets close to their stars, the Kepler data
doesn't actually represent the overall distribution and abundance of exoplanets.
Not accounting for that would be like trying to estimate the total number of humans
under two meters tall, by extrapolating from a database of basketball players.
This team claims to have gotten around that bias by developing a different algorithm
and incorporating some updated stellar information from another spacecraft.
And using these methods, they estimated that there's about
one Earth-like planet for every four Sun-like stars.
Considering that there are at least tens of billions of Sun-like stars in our Galaxy,
this seems like a huge deal.
That translates to billions of somewhat Earth-like planets.
But also, there's a massive amount of uncertainty in that estimate.
That number could actually be as low as one Earth per 33 stars,
or as high as one for every other star.
It depends on the parameters you use when playing with the data.
And even after all that, we still don't know what percent of those worlds
has a breathable atmosphere, or liquid water, let alone something game-changing like life.
It's an example of how hard astronomy can be, sometimes.
You'd think that counting planets would be easy,
but it takes time, and dedication, and a lot of information.
But it's also a job that some scientists are willing and excited to do.
And we are grateful for it.
Thanks for watching this episode of SciShow Space News!
If you enjoy exploring the vastness of the universe with us,
you might also like our new show that explores a much smaller universe.
It's called Journey to the Microcosmos, and it takes you on a dive
into the tiny, unseen world that is all around us.
It features footage from Jam's Germs, music from Andrew Huang,
and narration from me, but, like, much more chill than you might be used to.
And you can check it out at the link in the description.


A Baby Planet May Have Once Smashed Into Jupiter | SciShow News

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林宜悉 2019 年 9 月 23 日 に公開
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