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Bob the Alien's Tour of the Solar System
The Sun Mercury Venus Earth The Moon Mars Jupiter Saturn Uranus Neptune Pluto and Dwarf Planets Comets

Top of the Solar System

The Solar System's Twenty Largest Objects

Greetings, planet pickers! Welcome to Bob the Alien's Top of the Solar System! The Solar System is full of thousands of objects of various shapes and sizes - some unimaginably huge and some extremely tiny. Here is our rundown of the twenty largest items in the Solar System.
Number One
WIDTH ACROSS EQUATER
(DIAMETER)
1,392,000 kilometres
865,000 miles
CLASSIFICATION
AND LOCATION
Yellow dwarf star, centre of the Solar System
Topping our charts for what seems like an eternity and the undisputed holder of the title of Official Largest Object in the Solar System is everybody's favourite star, the Sun! At a width of 1,392,000 km (865,000 miles) and weighing in at 1,989,000,000,000,000,000,000,000,000,000 kilograms (whoever weighed it must have some pretty big scales!), the Sun is large enough to contain every single other object in the Solar System and is set to get even bigger as it gets older. It is almost ten times wider than the next largest object in the Solar System, which is......

The Sun

The Sun

Jupiter

Jupiter
Number Two
WIDTH ACROSS EQUATER
(DIAMETER)
142,984 kilometres
88,846 miles
CLASSIFICATION
AND LOCATION
Gas Giant. Fifth planet from the Sun, first of the Outer Planets
By Jove, it's Jupiter! Yes, second in our chart is the Solar System's largest planet and the first of the Gas Giants. Jupiter is a world made mostly of gas (hydrogen and helium if you're interested), hence the reason why it's called a Gas Giant. Scientists think that it may have a solid core surrounded by liquid metallic oceans, but they don't know for sure. In fact, they're probably just guessing. It could have a chocolate centre for all they know. Jupiter is a stormy world, with one storm in particular - The Great Red Spot - having raged for at least four hundred years. Keeping Jupiter company are at least 63 moons. Don't be surprised if some of them pop up later in this list.
Number Three
WIDTH ACROSS EQUATER
(DIAMETER)
120,536 kilometres
74,900 miles
CLASSIFICATION
AND LOCATION
Gas Giant. Sixth planet from the Sun, second of the Outer Planets
Jupiter's not-so-near neighbour is Saturn and it takes bronze position in this leaderboard of the Solar System's giants. Whoever or whatever created the Solar System seemed to like Saturn so much that they put a ring on it! With a similar gassy composition to Jupiter, Saturn also has a multitude of moons of all shapes and sizes orbiting it. Its diameter is 120,536 kilometres (74,900 miles), but if we take into consideration its ringspan, Saturn's diameter more than doubles to a whopping 270,000 kilometres (168,000 miles).

Saturn

Saturn

Uranus

Uranus
Number Four
WIDTH ACROSS EQUATER
(DIAMETER)
51,118 kilometres
31,763 miles
CLASSIFICATION
AND LOCATION
Gas Giant. Seventh planet from the Sun, third of the Outer Planets
Fourth on our list is the rather dull and featureless Uranus. But what it lacks it looks, it makes up in peculiarity. At some point in its history, Uranus fell over. Either this was because another large object collided with it and knocked it over, or it just felt like being different. Whatever happened, Uranus appears to orbit on its side, as if it is rolling around the Sun. Scientists are easily excitable creatures, and the effects of Uranus' sideways orbit excites them greatly. You see, its orbit causes Uranus to have an 'interesting' magnetic field, day and night to last forever (42 years), and its moons to orbit up and under the planet.
Number Five
WIDTH ACROSS EQUATER
(DIAMETER)
49,532 kilometres
30,779 miles
CLASSIFICATION
AND LOCATION
Gas Giant. Eighth and most distant regular planet from the Sun, fourth of the Outer Planets
When it was discovered in 1851, Neptune, the fifth object on our list, was the most distant planet in the Solar System. It lost its claim to this title in 1930 when Pluto was discovered, briefly regaining it for a few years in the late 1990s due to Pluto's weird orbit. However, when Pluto was permanently thrown out of the Planet Gang* in 2006 for being too strange, Neptune was once again given the title of Official Most Distant Planet in the Solar System (remember that if you're doing 'space travel brochures' kids!). Neptune is the last of the Gas Giants, representing the end of the region of the Solar System dominated by the huge gassy worlds. *Note: The Planet Gang doesn't actually exist. I just made it up.

Neptune

Neptune

Earth

Earth
Number Six
WIDTH ACROSS EQUATER
(DIAMETER)
12,756 kilometres
7,926 miles
CLASSIFICATION
AND LOCATION
Inner Planet. Third planet from the Sun
At number six is the Solar System's most unique, most special and most interesting object. It's none other than your home. Well, obviously, not your actual house, but the world on which it is situated. It's Earth, the first object in this chart with a solid surface, and therefore the first place you can actually stand on. The presence of water on its surface, a breathable atmosphere, a suitable climate and protection from the Sun's dangerous rays are all factors that allow Earth to be the ideal place for life. The planet is now home to countless lifeforms, and you are of course one of them! But, take care of Earth, because there's nowhere else to go.
Number Seven
WIDTH ACROSS EQUATER
(DIAMETER)
12,104 kilometres
7,521 miles
CLASSIFICATION
AND LOCATION
Inner Planet. Second planet from the Sun
With a size, mass, gravity and composition similar to Earth, Venus is often seen as its slightly smaller twin. If it is Earth's twin, Venus is most definitely an evil one. Something went drastically wrong with Venus at some point. If you were able to stand on its surface, you would be crushed, suffocated, cooked and pretty much doomed. Venus' surface pressure is similar to being 1km below water on Earth. Its atmosphere contains poisonous carbon dioxide, clouds contain sulphuric acid and temperatures are almost 500 C (900 F), hot enough to melt lead. And, even if you could survive, the fact that a day on Venus is longer than its year, and that it spins the wrong way, will just mess with your head! It's little wonder that Venus hides it horrors under a cover of deceptively beautiful clouds.

Venus

Venus

Mars

Mars
Number Eight
WIDTH ACROSS EQUATER
(DIAMETER)
6,794 kilometres
4,222 miles
CLASSIFICATION
AND LOCATION
Inner Planet. Fourth planet from the Sun.
Now this is more like it! Forget Venus and its inhospitality. Mars is much more accommodating, and over the years, the Red Planet has welcomed visitors aplenty, allowing rovers to drive across its surface, take pictures, poke its rocks and analyse its soil. Even so, it's still not somewhere that you'd go to in a hurry. With an unbreathable atmosphere, no water to drink (well, perhaps a small amount) and temperatures that are chilly to the extreme, Mars is not really the best place for a day out. That's not to say that life over there has been completely ruled out. Scientists continue to find evidence that could suggest that life could be or could have been possible on Mars.
Number Nine
WIDTH ACROSS EQUATER
(DIAMETER)
5,262 kilometres
3,270 miles
CLASSIFICATION
AND LOCATION
Moon of Jupiter. Eighth closest moon to Jupiter, third of the Galilean satellites
Unbelievably, the ninth and tenth largest objects in the Solar System happen to be moons. Well, I found it quite unbelievable when I found out. The Solar System's largest moon is Ganymede which orbits the Solar System's largest planet, Jupiter. Large enough to have been spotted by Galileo Galilei in 1610 through one of the first telescopes, Ganymede's surface is a mixture of extremely ancient and slightly less extremely ancient. Part of it is heavily cratered, much like many moons, whereas other parts are much smoother, suggesting that some sort of geological disturbance occurred after the period of heavy bombardment. Scientists reckon that deep below the surface, there may be water.

Ganymede

Ganymede

Titan

Titan
Number Ten
WIDTH ACROSS EQUATER
(DIAMETER)
5,510 kilometres
3,200 miles
CLASSIFICATION
AND LOCATION
Moon of Saturn. Twenty-first moon in orbit of the planet
The tenth largest object in the Solar System is Titan, the Solar System's second largest moon which orbits the Solar System's second largest planet, Saturn. What makes Titan unique is that it is the only moon in the Solar System to possess an atmosphere. And what an atmosphere it does possess! In fact, to be able to see through it, a probe had to be send to its surface to take pictures. Images sent back from the Huygens probe which landed in 2005 - along with radar imagery from the Cassini orbiter - revealed Titan to possess lakes of liquid methane. As well as methane in its atmosphere and frozen methane on its surface, the element plays a similar role on Titan as water does on Earth. Scientists sometimes consider Titan to be similar to an early Earth and some even consider the possibility of life there.
Number Eleven
WIDTH ACROSS EQUATER
(DIAMETER)
4,878 kilometres
3,031 miles
CLASSIFICATION
AND LOCATION
Inner Planet. Closest planet to the Sun
Because we're no longer allowed to call Pluto a planet, the final planet to feature in our chart, and therefore the smallest, is Mercury. Whizzing around the Sun in just 88 days, Mercury is scorched by the star on its sunlit side, yet is colder than cold on its 'night' side, its lack of atmosphere preventing the retention and dispersal of any of the heat that the planet receives.

Mercury

Mercury

Callisto

Callisto
Number Twelve
WIDTH ACROSS EQUATER
(DIAMETER)
4,821 kilometres
2,996 miles
CLASSIFICATION
AND LOCATION
Moon of Jupiter. Ninth closest moon to Jupiter, fourth of the Galilean satellites
It's back to Jupiter for now with Callisto occupying twelfth spot in our list. Callisto is the fourth of the Galilean satellites, Jupiter's four largest moons discovered by Galilei in 1610. Callisto is heavily cratered like most moons, but the rings around its craters appear quite bright suggesting that ice may be under its surface.
Number Thirteen
WIDTH ACROSS EQUATER
(DIAMETER)
3,643 kilometres
2,264 miles
CLASSIFICATION
AND LOCATION
Moon of Jupiter. Fifth closest moon to Jupiter, first of the Galilean satellites
Io, Io, it's off the Jupiter we go - again. The thirteenth largest object in the Solar System is Io, Jupiter's third largest moon and the closest of the four large Galilean satellites to orbit the planet. Io is a violent world where volcanoes erupt on a daily basis. The insides of Io are constantly churned and heated by the gravitational tug-of-war between Jupiter on one side and Europa, Ganymede and Callisto on the other. The resulting eruptions give the moon an ever-changing colourful appearance, and the discovery of active volcanoes there in 1979 revealed that Earth isn't the only only geologically active place in the Solar System, a discovery that undoubtedly excited many scientists.

Io

Io

The Moon

The Moon
Number Fourteen
WIDTH ACROSS EQUATER
(DIAMETER)
3,475 kilometres
2,159 miles
CLASSIFICATION
AND LOCATION
Natural satellite. In orbit of Earth
Next up is a very familiar face - Earth's Moon, or Luna if you want to give it its proper name. Thought to have formed out of the debris from a collision of a planet-sized object with Earth in the early days of the Solar System, the Moon is 400 times smaller than the Sun but, by some bizarre coincidence, is 400 times closer to Earth than the Sun. This means that the Moon and the Sun appear to be the same size from Earth and that the Moon can completely cover the Sun's disc during a total eclipse. The Moon is the only surface other than Earth to have been stepped on by human beings. The last one there stepped off it in 1972, and it doesn't look like anybody will be back in the near future.
Number Fifteen
WIDTH ACROSS EQUATER
(DIAMETER)
3,122 kilometres
1,940 miles
CLASSIFICATION
AND LOCATION
Moon of Jupiter. Sixth closest moon to Jupiter, second of the Galilean satellites
It's back to Jupiter for the final time, and time to acquaint ourselves with Europa. Unlike most moons, Europa's surface is smooth. This is because its surface is ice. It is thought that the ice is as much as 30 kilometres thick (18 miles) and that below it there may be water. As you know, or you should if you've read this website properly seeing as I keep harping on about it, water is essential for life. As Europa is thought to be covered in it, scientists are especially eager to investigate it. Who knows what kind of mysterious sea-dwelling creatures lurk in the depths of Europa's oceans? Not me, that's for sure.

Europa

Europa

Triton

Triton
Number Sixteen
WIDTH ACROSS EQUATER
(DIAMETER)
2,707 kilometres
1,680 miles
CLASSIFICATION
AND LOCATION
Moon of Neptune, seventh closest to the planet
It's over to Neptune now as its largest moon, Triton, takes sixteenth spot on our list. Triton is a cold, lonely place (well, I suppose everywhere other than Earth is lonely), so to pass the time and amuse itself, Triton orbits backwards and sometimes emits gasses. Nitrogen gas escapes through geysers in a similar, but less exciting, way to the volcanoes on Io. What this proves is that even distant moons are geologically active.
Number Seventeen
WIDTH ACROSS EQUATER
(DIAMETER)
3,000 kilometres
1,850 miles
CLASSIFICATION
AND LOCATION
Dwarf planet/Trans-Neptunian Object/Kuiper Belt Object/Plutoid. Most distant Dwarf planet in Solar System.
The newest entry in our chart, Eris' discovery in 2003 gave scientists headaches and many sleepless nights, resulting in catastrophe for Pluto. Being large and round, Eris, by definition, should have been a planet. But, astronomers around the world didn't want Eris to be a planet for reasons best explained elsewhere (here for example!) so they voted to change the definition of a planet. A new definition - the dwarf planet - was created for worlds just like Eris, would-be planets that exist in regions shared with other objects. Eris became one of the first dwarf planets. But so did Pluto, losing its status as planet and angering many a scientist and people from Illinois.

Eris

Eris

Pluto

Pluto
Number Eighteen
WIDTH ACROSS EQUATER
(DIAMETER)
2,390 kilometres
1,430 miles
CLASSIFICATION
AND LOCATION
Dwarf planet/Trans-Neptunian Object/Kuiper Belt Object/Plutoid. Usually orbits beyond Neptune
As if losing its status as a planet wasn't bad enough because of it, Eris' discovery also resulted in Pluto dropping a place in this chart. Pluto was discovered in 1930 by Clyde Tombaugh who was looking for a large planet beyond Neptune that was affecting Uranus' orbit. It later became apparent Uranus' orbit was not actually being affected by anything beyond Neptune, so Pluto's discovery was more through pure luck than anything else. Pluto's name was suggested by an English schoolgirl. From its discovery up to 2006, Pluto was the ninth planet in the Solar System. Nowadays, it is the Solar System's second largest dwarf planet.
Number Nineteen
WIDTH ACROSS EQUATER
(DIAMETER)
1,578 kilometres
982 miles
CLASSIFICATION
AND LOCATION
Moon of Uranus, seventeenth closest moon to the planet
Titania is a moon of Uranus and the largest moon to orbit the planet. It was discovered by William Herschel, the astronomer who discovered Uranus and three of its other moons. Not a lot is known about Titania. It is half ice and half rock and orbits above and below Uranus due to Uranus travelling around the Sun on its side.

Titania

Titania

Rhea

Rhea
Number Twenty
WIDTH ACROSS EQUATER
(DIAMETER)
1,530 kilometres
949 miles
CLASSIFICATION
AND LOCATION
Moon of Saturn, twentieth closest moon to the planet
Taking last spot in our list of the Solar System's largest objects is Rhea, the second largest moon of Saturn. It was discovered in 1672 by Giovani Domonico Cassini, although didn't get its name until 1847. Rhea is heavily cratered, and is home to a crater nicknamed "The Splat."