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  • [♪ INTRO]

  • The solar system, it turns out, is full of volcanoes, but not all of them spew or ooze

  • liquid rock, like you might tend to picture.

  • Where it's cold enough, we also see evidence of cryovolcanoes that spit out slushy ices.

  • So far, we've found them on several gas giant moons and on Pluto.

  • And we've even found one in the asteroid belt, on the dwarf planet Ceres.

  • Now, scientists reported this week in Nature Astronomy that they may have discovered up

  • to 31 more cryovolcano remnants on Ceres.

  • It's a volcano wonderland.

  • In 2015, NASA's Dawn spacecraft arrived at Ceres, and it's been mapping and studying

  • the object's surface ever since.

  • During its first year, Dawn found one cryovolcano that formed the mountain Ahuna Mons.

  • It's probably less than 240 million years old, which isn't that ancient when you're

  • talking about space volcanoes.

  • To really understand Ceres's history, researchers need to study older volcanoes.

  • But it's been harder to find any, because the material they're made out of sags and

  • flattens over time.

  • At least, that's what astronomers hypothesized.

  • To confirm that, the team analyzed images of Ceres's surface, looking for large structures

  • that might be flattened-out former cryovolcanoes, or, as they call them, viscously relaxed domes.

  • And they found a ton! Including Ahuna Mons, the team spotted a whopping 32 candidates.

  • Next, they used Dawn's camera to estimate the domes's heights.

  • For 10 of the 32 structures, they couldn't get clear enough data,

  • so they were excluded from the analysis.

  • But the rest were all over 1 kilometer tall.

  • Based on a set of assumptions, like how large the domes would have been when they started

  • out, and how much ice they contain, the team estimated the ages of these domes.

  • This time, they were able to date all but one.

  • They found that most of the structures were between 2 and 700 million years old,

  • but a couple were over 2 billion years old.

  • This all suggests that, over the last billion years,

  • Ceres got a new cryovolcano every 50 million years or so on average.

  • Besides teaching us more about Ceres's history, this study also supported the fact that cryovolcanoes

  • are really different from the hot, lava-spewing mountains on Earth.

  • For one, the icy magma on Ceres may originate in the dwarf planet's crust,

  • not in any sort of mantle like we see on terrestrial planets.

  • Ceres is also a lot less active.

  • This new study found that the total amount of matter put out by its cryovolcanoes is

  • between 1000 and 100,000 times less than that of the inner planets and the Moon.

  • Even if you account for surface area, terrestrial volcanic activity is still an order of magnitude higher.

  • This could mean that all cryovolcanic bodies, including places like Pluto and Europa,

  • have similarly low activity, but we'll need more data to know for sure.

  • Still, any day where you find a bunch of new volcanoes in the asteroid belt is a pretty good day.

  • Without a telescope or a good pair of binoculars, you probably won't be able to see Ceres from Earth.

  • But if you look up on a clear night, you might see a light

  • zooming across the sky for just a few seconds.

  • It's not a meteor, and it's probably not a UFO.

  • Instead, it's what's called a satellite flare: a satellite unintentionally catching

  • the light of the Sun and bouncing it down to you.

  • The brightest of these are called Iridium flares, but you'll only be able to see them

  • easily for a little while longer.

  • So consider this your heads-up.

  • These flares started around 1997, and they come from a group of

  • Low-Earth orbit communications satellites.

  • They're controlled by Iridium Communications Inc., hence the name.

  • They're not actually made of iridium or anything.

  • The flares come from sunlight bouncing off the three silver-coated antennae on each satellite.

  • If the angle is just right, they're bright enough to outshine Venus,

  • and even to be visible during the day.

  • But Iridium's network of 66 satellites is being replaced right now,

  • with a fleet of 75 smaller ones.

  • These new ones aren't the same shape, so they won't produce any flares.

  • As of July 2018, there have been seven successful launches to install new, flare-less satellites,

  • and the eighth and final launch is scheduled for November.

  • With the new guard coming in, some of the old satellites have already begun de-orbiting,

  • and they will be spiraling down until they're burned up by the Earth's atmosphere.

  • But they won't fall out of the sky all at once.

  • The different satellites all have their own paths to destruction, and for some of them,

  • that process could take up to 20 years.

  • So while the number of Iridium flares will drop drastically in the next year or so, you

  • might manage to catch one every once in a while.

  • It will just be much harder.

  • I remember when I was a teen, my dad took me out into the nighttime to be like,

  • there's the new iridium satellites,

  • and he timed it so that we could watch it together cuz he's a big nerd.

  • Today, since the satellites' orbits are actively controlled, it's really easy to

  • calculate when and where you need to be to see a flare, but that will change soon.

  • The good news for sky-watchers is that, even once the first Iridium satellites are gone,

  • other satellite flares will still be out there.

  • They're just not as spectacular.

  • And while you and I might be a little sad about that,

  • at least one group of people will be happy: astronomers.

  • Since Iridium flares are so bright, they tend to turn up as annoying streaks in study images.

  • So at least somebody's happy about these satellites

  • getting destroyed by the friction of the atmosphere.

  • If you're interested in checking out the last predictable Iridium flares,

  • the company has some resources to help you out, and we'll leave a link to them in the description.

  • They even have a bit of a social media campaign about it.

  • It's called #Flarewell, because they just, I guess they had to do that.

  • Thanks for watching this episode of SciShow Space News!

  • We've got a new piece of merch: These SciShow lab coats

  • which you might recognize if you watch SciShow Quiz Show.

  • But there's only a limited number of them, cuz we found them in a warehouse,

  • so if you want to look fancy in the lab, and show your support for SciShow,

  • head on over to dftba.com/scishow right now to pick one up!

  • It's got the normal pockets, and then it's got this pocket so that you can get your pocket,

  • inside pocket, without going like this. It goes like that.

  • [♪ OUTRO]

[♪ INTRO]

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發現。穀神星上有幾十座古老的低溫火山!| 科學秀新聞 (Found: Dozens of Ancient Cryovolcanoes on Ceres! | SciShow News)

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    林宜悉 發佈於 2021 年 01 月 14 日
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