Name: 太陽へ行った探査機の最初の成果 (First Results from the Probe That Went to the Sun)
Uploaded: 2021-01-14T10:27:38.000Z
Duration: 6 min
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程度の副詞

It affects pretty much everything that happens here on Earth

as well as all the other planets in the solar system.

But in some ways, we know shockingly little about what the Sun is actually like.

Now, that's about to change, thanks to the first results from NASA's Parker Solar Probe.

Parker set out for the Sun in August of 2018, and since then,

it's been looping around our star in tighter and tighter orbits.

So far, it's swung within 24 million kilometers of the Sun's surface,

more than twice as close as the orbit of Mercury.

And last week, in a set of four papers published in the journal Nature,

scientists revealed the results of Parker's first two flybys of the Sun.

The spacecraft's goal is to study the Sun's outermost layer, called the corona.

The corona is a thin layer of plasma that can reach millions of degrees Celcius.

a stream of electrically-charged particles moving outward from the Sun.

because it's only visible from Earth during a solar eclipse.

Now, though, in its first flybys, Parker is already starting to tell us more.

For instance, by the time the solar wind reaches Earth,

it has a pretty smooth, steady appearance,

but Parker's first measurements reveal that's definitely not true when it first gets going.

Close to the Sun, the solar wind looks far more turbulent.

Its charged particles latch onto the Sun's powerful magnetic field,

so as the Sun rotates, the wind gets dragged along for the ride.

And because every action has an equal and opposite reaction,

the energy it takes to drag the solar wind

also permanently slows down the spinning of the Sun itself.

I mean, just a little bit, but it's pretty amazing that a bunch of tiny particles

can put the brakes on something as big as the Sun!

Measuring the details of that process may help astronomers better understand

how young stars interact with the disks of gas and dust that surround them,

since scientists think that material is strongly connected to the magnetic field.

Speaking of which, Parker also showed that

the Sun's magnetic field is way more variable than scientists assumed in the past.

As it flew past the Sun, Parker repeatedly measured

nearly complete 180s in the field's direction.

So, instead of pointing away from the Sun like usual,

the magnetic field would point almost directly back towards it,

but this new information may offer clues about

the processes that get the solar wind flowing in the first place.

Finally, other Parker observations are only hints of what might be coming next.

Like, for a long time, astronomers have predicted that

dust that drifts too close to the Sun eventually gets vaporized,

leaving a dust-free zone around the star.

And now, the probe's cameras appear to be

detecting less dust floating around in space as it gets closer to the Sun.

scientists will have to wait for closer approaches.

Over the next five years, Parker will slowly lower its orbit

until it gets within just 6.5 million kilometers of the Sun.

In the meantime, the data will keep flowing.

Back in September, the probe made its third close approach,

so keep your eyes peeled for new findings in the months ahead.

We also got new details last week about a new instrument that was installed in April

on LIGO, the United States' gravitational wave observatory.

LIGO searches for ripples in spacetime, which radiate outward

from massive gravitational events like the mergers of black holes.

The new instrument is called the quantum vacuum squeezer,

and it sounds like it's straight out of Star Trek.

To understand what it does, first we need to talk about how LIGO works.

LIGO has two L-shaped detectors thousands of kilometers apart:

one in Washington State and another in Louisiana.

The two arms of the L intersect, and there's a set of mirrors where they meet.

On either end, a laser shines toward the mirrors.

Those mirrors reflect light back toward their source and onto a sensor.

If they travel exactly the same distance, they'll cancel each other out.

But if a gravitational wave washes over the detector,

it physically distorts space and briefly changes the length of the tubes.

Because it only distorts space in one direction,

it creates a slight difference in length between each arm of the L.

That means signals from the lasers won't perfectly cancel each other out.

So any time a mismatch is measured at both detectors,

it's a potential sign of a gravitational wave.

To make sure nothing disrupts the light from the lasers and creates a false signal,

the whole system operates in a nearly perfect vacuum.

On the tiniest scales, the effects of quantum mechanics

mean that particles like photons are popping in and out of existence all the time.

If some of those extra photons hit the special light sensors,

they can add uncertainty to the distance measurement

Scientists call this effect quantum vacuum noise.

And that's where the quantum vacuum squeezer comes in.

This noise has two basic qualities: phase and amplitude.

Phase affects the timing of when photons arrive at the light sensor,

while amplitude describes how many photons there are.

A quantum vacuum squeezer is a special instrument made of crystals and mirrors

that can basically exchange one kind of quantum fluctuation for the other.

In the case of LIGO, variation in phase is more of a problem than variation in amplitude,

so the squeezer narrows down the range of possible phases,

Explaining exactly how this device works would probably require a whole series of videos.

But the end result is that LIGO is more sensitive to gravitational waves.