Download The Planets

The Planets
By Rachael Brennan
The Sun
All the planets in the solar system travel around the Sun in an ellipse
shape.
On Earth it takes us about 365 days (or 1 year) to complete 1 orbit
around the Sun, although a year is different on each planet.
How Do Planets Form?
As we currently understand it, a star and all its planets form out of a collapsing cloud of gas
and dust.
Gravity pulls all the material in this cloud closer and closer together, and so the centre of
the cloud gets more and more compressed.
This all then begins to heat up, with the dense, hot core becoming the beginning of a new
star – our Sun!
If you go back in time about 4.6 billion years, you’ll find a swirling, slightly glowing mess of
dust and gas just like that – soon to become our new home in the universe.
As the cloud continues to compress, most of it begins to rotate in the same direction –
which is actually why all the planets are still rotating in the same direction today; it never
stopped spinning!
This spiral cloud flattens into a disk, and it’s here that the planets are formed.
The Sun
The Sun is 4.567 billion years old, just a little older than Earth.
Its circumference is 4,367,000km or 2,713,000 miles, which is 109 times bigger than Earth.
The mass of the Sun is equivalent to 333,060 times bigger than that of Earth’s mass.
1,301,019 Earths could fit inside the sun.
Its density is much less than Earth’s, by 0.256 times.
Gravity on the Sun is much stronger than ours – it is 28 times more powerful.
The Sun accounts for almost all of the mass in the solar system – around 99% of it, in fact.
The remaining 1% is left for all of the planets and everything else in the system.
The Rocky Planets
Immediately surrounding the Sun we find the 4 rocky planets (also known as the
terrestrial planets):
• Mercury
• Venus
• Earth
• Mars
They’re mainly composed of rocks and metals;
They each have a central core that is mostly made of iron;
They all have a solid surface with familiar features to us: mountains, canyons,
volcanoes and the like.
Mercury
Circumference:15,329km (or 9,524 miles), which is 0.06 times Earth’s.
Mass:0.56 times Earth’s.
Volume: 0.06 times Earth’s.
Temperature:This varies wildly, from 427°C during the day to -173°C at night.
Rotation:It takes Mercury 58½ Earth days to make 1 rotation on its axis.
Orbit:A super fast 88 days to go around the Sun!
Moons:None
Gravity:0.38 times that of Earth, so 100kg on here would weigh 38kg on Mercury.
Magnetic field:Very low, just under 1% of Earth’s.
Given that Mercury is the closest planet to the Sun, you might also assume it to be the
hottest in the solar system, but that title actually belongs to Venus. In fact, Mercury is so
close to the Sun that it doesn’t even have an atmosphere – the solar winds the Sun emits
blows away any atoms from the surface of the planet, leaving it bare.
Venus
Circumference:38,025km or 23,627 miles, very similar to that of Earth – just a bit smaller.
Mass:0.82 times Earth’s.
Volume:0.857 times Earth’s.
Temperature:462°C on average.
Rotation:It takes Venus 243 days to do 1 rotation on its axis.
Orbit:225 days to go around the Sun.
Moons:None.
Gravity:0.9 times that of Earth’s, so 100 kg on Earth weighs 91kg on Venus.
Magnetic field:Venus doesn’t generate a magnetic field.
Venus is sometimes known as Earth’s twin due to the two planets’ similarities in terms of
size and mass, and its thick clouds reflect an awful lot of the Sun’s light, making it the
brightest object in the sky after the Sun and moon.
Mars
Circumference:21,297km or 13,232 miles.
Mass:0.11 times Earth’s.
Volume:15% times Earth’s.
Density:0.714 times Earth’s.
Temperature:-63°C on average.
Rotation:Mars takes 24.5 hours to complete 1 rotation on its axis.
Orbit:687 days to go around the sun.
Moons:2, Phobos and Deimos (meaning fear and panic), both of which have been
described as being potato shaped.
Gravity:Just 37% of Earth’s, so 100kg on Earth would weigh 38kg on Mars.
Magnetic field:Very weak.
Mars is currently considered humanity’s best bet for a new planet to colonize.
The Gas Giants
Beyond the terrestrials and the Asteroid Belt lie the most massive planets in our
solar system – the 4 gas giants:
• Jupiter
• Saturn
• Uranus
• Neptune
Unlike the 4 rocky terrestrial planets, these are made up mostly of gas, and have no
solid surface on which you could stand.
They’re also much further away and more spread out than the terrestrials are; in
fact, Neptune and Uranus are so far out and icy cold that they’re actually classified
as ice giants.
Jupiter
Circumference:439,246km (272,946 miles), 11 times the size of Earth.
Mass:318 times that of Earth.
Volume:1,321 Earths could fit inside Jupiter.
Density:0.24 times Earth’s.
Temperature:About -148 °C at the top of its clouds.
Rotation:Jupiter spins once on its axis every 9 hours and 55 minutes.
Orbit:It takes Jupiter 11.86 years to complete one trip around the Sun.
Rings:It has 3 rings, although they’re very hard to see.
Gravity:2.64 times Earth’s so 100kg on Earth would weigh 253kg on Jupiter.
Magnetic field:20,000 times Earth’s.
Moons:67 as of 2015 – Jupiter loses and gains them, so the count goes up and down. The
for largest moons are Io, Europa, Ganymede and Callisto.
Jupiter is the biggest planet in the solar system. It alone takes up ⅔ of the mass of all the
planets combined and, by volume, it would be possible to fit all the other planets in the
solar system inside it.
Saturn
Circumference:365,882km (227,348 miles), 9 times larger than Earth.
Mass:95 times Earth’s
Volume:Around 755-764 Earths could fit inside Saturn.
Density:0.125 times Earth’s.
Temperature:-178°C at the top of its clouds.
Rotation:Saturn spins once on its axis every 10.7 hours.
Orbit:It takes Saturn 29.5 years to travel once around the Sun.
Gravity:Very similar to Earth, 100kg on Earth would weigh 107kg on Saturn.
Magnetic field:578 times more powerful than Earth.
Moons:62, with 53 of those known and 9 still awaiting confirmation. The most well known are:
Titan, Enceladus, Lapetus, Mimas, Tethys, Dione and Rhea.
Saturn is popularly known as “Jewel of the solar system” for its beauty and it also has 5 rings. It is
actually the only planet in the system that is less dense than water – meaning that if you were to
put it in a swimming pool, Saturn would float!
Uranus
Circumference:159,354km (99,018 miles), nearly four times the size of Earth.
Mass:About the same as 14.5 Earths.
Volume:63 Earths could fit inside Uranus.
Density:0.23 times Earth’s.
Temperature:About -220°C at the top of its clouds.
Rotation:Uranus takes 17 hours to complete 1 rotation on its axis.
Moons:27 known moons. None are very big, and the largest are Oberon and Titania – almost all of them
are named after Shakespeare’s plays.
Gravity:Similar to Earth, 100kg on Earth would weigh 91kg on Uranus.
Magnetic field:48 times more powerful than Earth.
Rings:13, but they’re very faint and can only be seen with special equipment.
Orbit:It takes Uranus 84 years to travel once around the Sun.
Uranus is actually tilted on its axis by a massive 98°, meaning that instead of spinning around like all the
other planets do, it rolls around the Sun like a ball! It’s thought this probably happened in its early life
when it collided with another planetary body, sending it a bit off–course. It also rotates in the opposite
direction to the other planets (with the exception of Venus). It also almost ended up with an entirely
different name: George.
Neptune
Circumference:154,705km (96,129 miles), nearly four times as big as Earth.
Mass:17 times that of Earth’s.
Volume:58 Earths could fit inside of Neptune.
Density:0.3 times that of Earth’s.
Temperature:-218°C at the top of its clouds.
Rotation:It takes Neptune 16 hours to spin once on its axis.
Orbit:Neptune takes just over 165 years to travel once around the Sun.
Density:0.6 times Earth’s.
Gravity:Quite similar to Earth’s, 100kg here would weigh 114kg on Neptune.
Magnetic field:27 times more powerful than Earth’s.
Moons:13 confirmed, and one is pending. Its most significant moon is Triton.
Triton has a strange backwards orbit that means, year by year, it’s getting closer and closer to
Neptune. This probably means that Triton used to be a dwarf planet that Neptune captured in its
orbit. When these 2 bodies finally collide, Triton will be torn to pieces and will form a ring around
Neptune, just like Saturn’s! This won’t be happening for about 3.6 billion years though.
Earth
The Earth is made up of 3 main layers:
• Crust (at the top)
• Core (at the centre)
• Mantle (in between the core and crust)
Then, above the Earth is the atmosphere, which is divided into 5 different layers:
• Atmosphere
• Troposphere
• Stratosphere
• Mesosphere
• Thermosphere