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#### 我们太阳系的行星：木星

Our Solar System's Planets: Jupiter

Hi I’m Alex McColgan, and welcome to Astrum.

It’s been a long time coming and after a lot of requests,

here is everything you could want to know about Jupiter.

It is a massive planet.

The largest in our Solar system.

It is so massive,

its mass is 3/1000th that of our sun

that might not seem a lot,

once you realize that sun contains 99.86%

of all the mass in the solar system

you’ll realise that Jupiter equals almost the remainder.

Its mass is two and a half times that of all

the other planets in the solar system combined.

And this brings about an interesting phenomenon,

the barycentre between Jupiter and the Sun is actually

above the surface of the Sun,

at 1.068 solar radii from the Sun’s centre.

What is a barycentre I hear you ask?

you see, when we think of an object orbiting another object,

we don’t necessarily think

that the smaller object has a gravitational influence on the bigger object.

So the definition of a barycentre

is the centre of mass between these two objects.

With Jupiter being the size it is,

it doesn’t orbit anywhere close to the centre of the Sun.

The orbit in fact looks more like this

with Jupiter and the Sun rotating around the barycentre.

in this case the barycentre is above the surface of the Sun.

Still don’t believe me?

Have a look at this.

I want to give you a really crude representation of what a barycentre is.

So here we have the Sun and Jupiter,

and we find that the centre of mass

is much closer to the Sun than it is to Jupiter.

While Jupiter has the greatest mass of any planet in the solar system,

it’s not the densest planet.

It is the most massive only because it is the biggest.

If Neptune was the same size as Jupiter,

it would be the most massive.

And if Jupiter was the same size as Earth

Earth would be over 4 times more massive.

As it is though,

the diameter of Jupiter is 11 times that of Earth,

and its total mass is 318 times more than Earth.

As we know, mass affects gravity.

This means that Jupiter has a huge gravity,

over twice that of Earth at 2.528g at its surface.

The gravity of Jupiter affects every planet toone degree or another.

It is strong enough to tear asteroids apart

and capture 67 moons at least.

Some scientists think that

Jupiter destroyed many celestial objects in the ancient past

as well as preventing other planets from forming.

At the moment though,

it could be the hero of the inner 4 planets.

Without Jupiter acting as a “cosmic vacuum cleaner ”,

it wouldn’t be sucking up dangerous objects like long-period comets,

or perturbing their orbit enough or giving them a little kick of energy

so that they leave the solar system altogether.

And a question I always had as a child,

could Jupiter become a star?

Surely someone just needs to throw a match in

seeing as it’s made of flammable hydrogen.

Sadly, anyway,current thinking is that Jupiter would need to be

roughly 75 times more massive than it is now

to be massive enough to be a star,

although its volume isn’t too far off from the smallest known red dwarf.

Jupiter is the 5th planet from the Sun,

and it’s 5 times further away from the Sun than Earth.

Even so, it can be the 3rd brightest object in the night sky

after the moon and Venus.

I just want to show you how bright that is.

Just using a handy cam,

we can see Jupiter quite easily in the night sky.

With a maximum apparent magnitude of -2.94,

As a result of it being so obvious in the sky,

it makes a very nice target for amateur astronomers.

One of my subscribers was kind enough to show what he saw

when Jupiter pass by the moon.

With good magnification,

you can see its patterns quite clearly.

And what makes these patterns?

The cloud layer itself is only about 50km thick

and contains ammonia crystals much like on Saturn,

but the colouration comes from compounds

heating up from deep within Jupiter and then rising.

These compounds are known as chromophores

and when they reach the clouds,

they interact with the UV light of the Sun

to create these spectacular multi-coloured bands.

This is quite the cycle though,

and the face of Jupiter can change dramatically over time.

Even if their colours do change though,

the actual latitude of these bands

remains consistent enough to be given identifying designations,

but they can vary in width over the course of time.

Lots of storms and turbulence occur where the bands meet

and it is the reason Jupiter has the very famous great red spot.

This storm is huge.

It can easily fit the diameter of Earth within it.

It has existed for as long as we know

since it was first discovered in the 17th century.

It might very well be a permanent feature of the planet,

but interestingly it has decreased in size

since observations began.

The reason for its reddish colour is unknown,

and the colour of the spot can vary greatly
——从砖红变成几乎全白
– from brick red to almost white.

The most recent theory for its colour

is chemical compounds being broken up by the UV light of the Sun,

much in the same way as the process that happens on the rest of the planet.

The storm is actually much higher up in the atmosphere than the surrounding clouds

and as a result can interact with the sunlight a lot more

This would explain why its colour

can be much stronger than anything else around it.

Another storm, known as “ Red Spot Jr ”,

formed when three storms merged into one

and it has so far passed unscathed by its bigger neighbour

and is now quite a prominent feature of the planet.

It could last for another couple of hundreds of years

if it avoids the same fate of a similar storm

which passed right through the heart of the Great Red Spot.

So what do we think Jupiter is made of?

or much like Saturn, under the atmosphere are gaseous,

then liquid, then metallic forms of hydrogen.

The further into the planet you go,

the greater the pressure becomes.

under immense pressure, hydrogen acts as a metal.

And beneath that is an ice or rocky core.

Because we can’t recreate on Earth the immense pressures Jupiter experiences,

we don’t really know what properties

these materials have at the core.

Roughly 90% of Jupiter is thought to be hydrogen,
10%是氦气 还有微量的甲烷
10 % helium, and then trace amounts of methane,

ammonia and others.

And yes, you may have noticed on this picture,

Jupiter does indeed have rings.

Nothing on the scale of Saturn,

but there are 4 planetary rings.

The main ring is very thin but bright,

the rest quite wide but exceptionally faint.

The main ring is about 6,500km wide,

and the only distinctive feature you will see

is what is known as the Metis notch.

Something else of note about Jupiter

is its remarkably strong magnetosphere.

It is 14 times stronger than Earth’s,

due to the planet’s liquid metallic hydrogen centre.

This makes it the strongest magnetosphere of any planet in the solar system

and it’s beaten only by the Sun’s sunspots.

There are a couple of reasons why this is really interesting.

The first being that

magnetospheres channel solar wind to the planet’s pole

which produce magnificent aurorae.

The second is that the four biggest moons of Jupiter

are protected from this solar wind

because they orbit within the magnetosphere.

This implies they don’t need their own strong magnetospheres

because Jupiter is doing that for them.

And I’ll just very quickly talk about the Moons,

because I want to save them for a futurevideo.

Jupiter has 67 known natural satellites.

51 are under 10km in diameter

but the largest,”the Galilean moons”

are some of the biggest in the solar system.

They are Io, Europa,

Ganymede and Callisto,

and they are all interesting in their own right.

Ganymede is actually the biggest moon in the solar system

and has a greater diameter than that of Mercury.

We’re almost at the end of this video sadly,

but we’ll just finish by talking about the orbit and rotation of Jupiter.

Jupiter like I mentioned before

is the 5th planet from the Sun,

it’s found on the outskirts of the asteroid belt

and sits in between the orbits of Mars and Saturn.

It is 778 million km away from the Sun on average

or 5.2AU,

it completes its orbit from the sun every 12 Earth years.

The axial tilt of the planet is small, only 3 degrees.

This means it doesn’t experience much change in seasons,

unlike Earth and Mars.

And very much like Saturn, its radius at the equator

is greater than at the poles.

It rotates very fast, faster than any other planet,

completing a rotation in only 10 hours.

But due to it not being solid,

it doesn’t rotate the same speed all over,

The rotation at the poles taking 5 minutes longer than at the equator.

And with this final thought

take a look at Jupiter through the infrared.

Demonstrating the immense size and power of this planet,

this dot at the bottom of the planet

is the impact of an object from space,

which if it had hit Earth,

could have spelled the end of our planet as we know it.

We can be glad Jupiter is there,

not only for its beauty,

but also because in so many ways

it is an asset to our solar system.

Thank you so much for watching this far.

Did you learn something today about Jupiter

you never knew before?

What other things do you know

that I didn’t include in this video?

I would most humbly ask that

you share it with friends, family, neighbours and acquaintances

as I put a lot of time into these videos,

and if this channel really takes off

I would be able to do it full time

which mean for you a lot more videos

And what would you like to see next on this channel?

and I’ll see you next time.