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. Jupiter
It is a massive planet. The largest in our Solar system. It is so massive, it is 1/1000th
that of our Sun. That might not sound a lot, but once you realise the 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? Well 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 to
one degree or another. It is also 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. They even predict the gravity
of Jupiter is perturbing Mercury’s already eccentric orbit enough that in a few billion
years the tiny planet may either crash into the Sun or be ejected from the solar system
altogether. [end video] 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, current
thinking is that Jupiter would actually 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 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, it can actually cast shadows.
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 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, 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 – 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 sunlight a lot more. This would explain
why its colour can be much stronger than anything 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? Well 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.
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% 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 can 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 future
video. Jupiter has 67 known natural satellites. 51 are under 10km in diameter, but the 4 largest,
“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 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, and completes its
orbit 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, a 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 and make more of
these kinds of videos in the future much faster. And what would you like to see next on this
channel? Post in the comments below, and I’ll see you next time.