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  • Narrator: We have a mysterious new kid on the block.

  • Astronomers call it Oumuamua.

  • Which in Hawaiian, roughly translates to

  • "first time visitor from far away."

  • Oumuamua is the first interstellar object

  • ever detected in our solar system.

  • Astronomers discovered it in 2017

  • with the Pan-STARRS1 telescope.

  • And like all grand discoveries,

  • it has raised more questions than it answers.

  • Where did it come from?

  • What's it made of?

  • And yes, even the ultimate query, is it aliens?

  • That's what two Harvard astrophysicists posed

  • in a recent paper,

  • suggesting that Oumuamua could be some type

  • of alien spacecraft.

  • And when we spoke with one of them,

  • the idea didn't sound as far-fetched as you might think.

  • Loeb: I prefer to adopt the maxim of Sherlock Holmes

  • that if you rule out the impossible,

  • whatever remains, as improbable as it is,

  • must be the truth.

  • Narrator: Now a good rule of thumb

  • is that aliens are always the least likely answer.

  • But here's the thing, the more reasonable explanation

  • right now isn't panning out.

  • Most astronomers think that Oumuamua

  • is probably a stray comet from another stellar system.

  • The only problem is that it doesn't look like any comet

  • we've ever seen,

  • because it appears to lack that iconic tail.

  • Loeb: There was an anomaly seen in the data.

  • And it cannot be explained

  • by the most conventional explanation,

  • which in this case is a cometary outgassing.

  • And so we propose an alternative interpretation

  • which is the only one I can think of.

  • Narrator: But it seems extreme to assume aliens

  • just because Oumuamua doesn't look like a comet, right?

  • Not when the Harvard scientists accounted

  • for another peculiarity.

  • As Oumuamua traveled through our solar system,

  • it didn't follow the normal path of a typical comet

  • under the sun's gravity.

  • Rather, it slightly shifted off course,

  • which couldn't be explained by gravity alone.

  • Something else, some unknown force was also at play,

  • manipulating the object's behavior.

  • Loeb: I cannot think of any other possibility

  • other than the outgassing that we find in comets,

  • which seems to be ruled out

  • because we don't see a cometary tail,

  • or the pressure from the sunlight.

  • There is no other proposal on the table right now.

  • Narrator: Pressure from sunlight.

  • It works similarly to how wind

  • pushes against a sail on a boat.

  • So too can sunlight push against a spacecraft

  • to propel it through space.

  • Incidentally, we call these spacecraft solar sails.

  • There's just one catch.

  • Pressure from sunlight is extremely light.

  • Lighter than the weight of a fly on your hand.

  • Which means in order for it to be effective,

  • solar sails also have to be extremely light and thin.

  • In 2010, for example, Japan's space agency

  • launched its Ikaros solar sail,

  • which only weighed 1.1 pounds.

  • But it eventually managed to travel over 65 million miles

  • from Earth on just sunlight alone.

  • And it's this type of force that the Harvard scientists

  • think could be propelling Oumuamua too.

  • Of course, that's if it's an alien made sail

  • in the first place.

  • Loeb: Well first of all, I am not confident

  • that this is the correct interpretation

  • because we don't have enough data.

  • And so this is one possibility.

  • I would highly recommend people to read the paper.

  • If they have a better idea, they should publish it.

  • Narrator: And as always, not everyone agrees

  • with Loeb's hypothesis.

  • Weryk: I think that their explanation,

  • I think it's in contrast with what the data says.

  • You know, we did consider that possibility

  • in our own paper, which was published earlier,

  • and we dismissed it as not being physically valid.

  • You know again, there's no reason to think Oumuamua

  • is anything but a natural object.

  • Narrator:That's Rob Weryk,

  • who first discovered Oumuamua in 2017.

  • Weryk: So we think Oumuamua still has ice

  • and the sublimating ice gives it a small tiny kick

  • that gravity alone wouldn't account for,

  • but that the dust it has is much larger

  • than what comets typically have.

  • And so we just don't see that from the ground.

  • Narrator: And yes, in all probability, he's right.

  • Oumuamua is a natural object,

  • like a comet or asteroid.

  • But neither Weryk nor Loeb can know for sure

  • without more data.

  • And sadly, Oumuamua is on its way out of the solar system

  • beyond the reach of our telescopes.

  • So the best bet for solving this mystery?

  • Weryk: So for Oumuamua itself, it's basically gone,

  • it's too faint to see from the ground.

  • There's no way we could send a spacecraft mission,

  • so we really have to find a second object.

  • That would help answer a lot of questions

  • that we don't know.

  • You know, I'm very interested in finding a second one.

  • It'd be nice if I found them all.

  • Narrator: And Loeb already has some ideas

  • on where to look next.

  • Loeb: There should be quite a lot of them

  • right now in the solar system.

  • And some of them could be trapped by Jupiter and the sun

  • that act as a fishing net.

  • And so some of these interstellar objects

  • are bound to this solar system after the first passage.

  • Narrator: That's right.

  • Some of these interstellar objects

  • might be right here in our solar system,

  • trapped, and waiting to be found.

  • It looks like astronomers may have

  • more fascinating discoveries to come.

Narrator: We have a mysterious new kid on the block.

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B1 中級 美國腔

哈佛科學家為何認為這個物體是外星飛船? (Why Harvard Scientists Think This Object Is An Alien Spacecraft)

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    瀾雁 發佈於 2021 年 01 月 14 日
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