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  • When you look at Earth today, it's easy to imagine that it formed as a perfect, fertile planet,

  • full of everything it needed to support life.

  • It's a beautiful, big, wet rock.

  • But scientists are pretty confident that's not what happened.

  • They've known for a long time that, because of Earth's early conditions,

  • the key ingredients of life, elements like carbon and nitrogen, have not been here since the beginning.

  • Popular hypotheses suggest they arrived via meteorites or comets,

  • but none of those models totally checks out.

  • So now, there's another idea.

  • Last Wednesday, in a paper published in Science Advances,

  • researchers announced that these elements most likely made a more dramatic arrival.

  • Instead of coming on meteorites, they may have come from a massive collision.

  • The same massive collision that formed the Moon.

  • Now it's not surprising that these elements, called volatiles, came from elsewhere.

  • They have really low boiling points, so when Earth was forming,

  • it would have been way too hot to hold onto them.

  • And also, thanks to their chemistry, any volatiles that didn't escape

  • would likely have been pulled into the Earth's iron core.

  • So, somehow, they must have been added to the mix later.

  • Otherwise, we wouldn't be here.

  • It's just that figuring out thatsomehowis much easier said than done.

  • Like, even though the idea about Earth getting its volatiles from meteorites is popular,

  • the numbers have never quite added up.

  • Earth's ratio of carbon to nitrogen is way higher than that of any meteorite.

  • So in this new study, a team of researchers at Rice University got creative to try and

  • understand what happened.

  • In their lab, they used machinery to put rocks under extremely high pressure and temperature,

  • squeezing them as if they were around 100 kilometers below the Earth's surface.

  • They were trying to recreate the environment that would have existed when planets' cores were forming.

  • And they found something interesting.

  • In their experiments, a planet with an iron core would normally pull in all the volatiles,

  • just like on Earth.

  • But if that core was rich with sulfur, the volatiles were less attracted to it,

  • so they remained free.

  • That doesn't mean much for Earth itself, since our planet doesn't have a sulfur-rich core.

  • But it does mean that a foreign rock with a core like that could have had plenty of

  • volatiles in its outer layers.

  • So if an object like this collided with Earth at some point,

  • it could have contaminated our planet with those elements that earth had long ago lost.

  • You might be thinking that sounds like a lot of sketchycould have”s,

  • but the researchers found that it was surprisingly likely.

  • They ran around a billion simulations of the evolution of the solar system,

  • and found that the best explanation for the number and ratio of volatile elements on Earth is a scenario

  • where an object around the size of Mars collides with our planet.

  • Now as for the timeline, in the best-fit scenario, the collision lined up with the one that formed the Moon.

  • It's a promising, and really convenient, idea, but the case isn't closed yet.

  • This study mainly looked at the chemistry that might have happened during a collision,

  • but we'll need to learn more about the physical side of how planets grow and evolve.

  • Still, if proven, this research backs up the idea that, in all likelihood,

  • we owe our whole existence to the colliding worlds of the early solar system.

  • Of course, it's not easy to decode the solar system's history billions of years after events took place.

  • Fortunately, some clues are locked away at the edge of our solar system,

  • and scientists are starting to uncover them.

  • On Monday, in the journal Nature Astronomy, researchers announced that they may have indirectly detected

  • a kilometer-sized rock in the Kuiper belt, the ring of icy objects past Neptune.

  • If true, it would be the first time astronomers made a detection of an object like this on two separate telescopes,

  • making it the most convincing detection yet.

  • These barren rocks might not seem like they have much to do with us,

  • but they're kind of like long-lost relatives.

  • Earth and the other planets formed from objects like those.

  • The difference is that this icy fringe of the solar system wasn't dense enough to form planets,

  • so it's barely evolved at all in the last 4.6 billion years.

  • So in the absence of time travel, it's the closest we can get to seeing what things were like

  • when the planets were first forming.

  • In the study, scientists were especially interested in finding objects between one and 10 kilometers across,

  • because rocks like these formed the seeds of our planets.

  • Unfortunately, objects that size are way faint.

  • Like, much fainter than Pluto, so even the largest telescopes can't see them directly.

  • But, in theory, and maybe now for the first time in practice, we can detect them indirectly

  • by measuring blips in the light as they pass in front of stars.

  • It's a method called a stellar occultation.

  • And it's not easy to pull off.

  • That blip in light is very small and lasts less than a second, and with just one telescope,

  • it can be embarrassingly difficult to tell between a 4.6-billion-year-old space rock

  • and, like, a bird that flew past.

  • So the team in this study set up two identical telescopes on the roof of a school in Japan,

  • and monitored around 2000 stars for just over a year.

  • After sifting through more than 100,000 hours of data, they found what they were looking for:

  • one possible detection of a Kuiper belt object passing in front of a star.

  • So far, it's just a candidate.

  • Even though the chances are really small, we can't entirely rule out the possibility

  • that the signal came from a statistical fluke, or something like an asteroid.

  • But if it is real, this tiny shadow can still offer some insight.

  • Making some assumptions about its shape and position, scientists peg its diameter at around 1.3 kilometers.

  • That supports previous results that suggest there may be more small objects in the Kuiper belt

  • than some studies previously thought.

  • And the better we understand how they're distributed,

  • the better we can understand what kinds of objects grew into the planets and which ones stayed behind.

  • To get closer to that answer, the team and their collaborators plan to keep looking for

  • other occultations that can tell us more about these ancient rocks and the history we share with them.

  • So, between our observations and simulations,

  • we can start to fill in some of the holes in our solar system's majestic history.

  • Thanks for watching this episode of SciShow Space News!

  • And especially thank you to all the people who support us on Patreon,

  • helping us unpack science news like this.

  • We love doing what we do and we're very thankful to have you on board.

  • If you want to support the show and partner up with a bunch of other curious, wonderful people,

  • you can go to patreon.com/scishow.

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The Moon's Birth May Have Given Earth Ingredients for Life | SciShow News

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    林宜悉 posted on 2020/03/30
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