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  • [♪ INTRO]

  • 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.

  • [♪ OUTRO]

[♪ INTRO]

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赤ちゃんの惑星が木星に衝突したことがあるかもしれない|サイゾーウーマンニュース (A Baby Planet May Have Once Smashed Into Jupiter | SciShow News)

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    林宜悉 に公開 2021 年 01 月 14 日
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