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
Yellow dwarf star, centre of the Solar System
Diameter: 1,392,000 kilometres / 865,000 miles
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 almost 2 million million million million million 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......
Gas Giant. Fifth planet from the Sun, first of
the Outer Planets
Diameter: 142,984 kilometres / 88,846 miles
By Jove, it's Jupiter
! Yes, second in our chart is the Solar System's largest planet and the first of the
is a world made mostly of gas (hydrogen and helium if you're interested), hence the reason why it's called a
. 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.
is a stormy world, with one storm in particular -
The Great Red Spot
- having raged for at least three hundred years. Keeping Jupiter company are at least
. Don't be surprised if some of them pop up later in this list.
Gas Giant. Sixth planet from the Sun, second
of the Outer Planets
Diameter: 120,536 kilometres / 74,900 miles
not-so-near neighbour is
and it takes bronze position in this leaderboard of the Solar System's giants. Whoever or whatever created the Solar System seemed to like
so much that they put a ring on it! With a similar gassy composition to
also has a multitude of
of all shapes and sizes orbiting it. Its diameter is 120,536 kilometres (74,900 miles), but if we take into consideration its ringspan,
diameter more than doubles to a whopping 270,000 kilometres (168,000 miles).
Gas Giant. Seventh planet from the Sun, third
of the Outer Planets
Diameter: 51,118 kilometres / 31,763 miles
Fourth on our list is the rather dull and featureless
. But what it lacks in looks, it makes up in peculiarity. At some point in its history,
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,
appears to orbit on its side
, as if it is rolling around the
. Scientists are easily excitable creatures, and the effects of
' sideways orbit excites them greatly. You see, its orbit causes
to have an 'interesting' magnetic field, day and night to last forever (42 years), and its
to orbit up and under the planet.
Gas Giant. Eighth and most distant regular
planet from the Sun, fourth of the Outer Planets
Diameter: 49,532 kilometres / 30,779 miles
When it was discovered in 1851,
, 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
was discovered, briefly regaining it for a few years in the late 1990s due to
weird orbit. However, when Pluto was thrown out of the Planet Gang* in 2006 and became a dwarf planet,
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!).
is the last of the Gas Giants
, representing the end of the region of the Solar System dominated by the huge gassy worlds. It's a very cold and windy world, the windiest of all of the planets. *Note: The Planet Gang doesn't actually exist. I just made it up.
Inner Planet. Third planet from the Sun
Diameter: 12,756 kilometres / 7,926 miles
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
, 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
dangerous rays are all factors that allow
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
, because there's nowhere else to go.
Inner Planet. Second planet from the Sun
Diameter: 12,104 kilometres / 7,521 miles
With a size, mass, gravity and composition similar to
is often seen as its slightly smaller twin. If it is
is most definitely an evil one. Something went drastically wrong with Venus at some point. If you were able to stand on its
, you would be crushed, suffocated, cooked and pretty much doomed. Venus' surface pressure is similar to being 1km below water on Earth. Its
contains suffocating 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
is longer than its year, and that it spins the wrong way, will just mess with your head! It's little wonder that
hides it horrors under a cover of deceptively beautiful clouds.
Inner Planet. Fourth planet from the Sun
Diameter: 6,794 kilometres / 4,222 miles
Now this is more like it! Forget
and its inhospitality. Mars
is much more accommodating, and over the years, the Red Planet has welcomed
, 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,
is not really the best place for a day out. That's not to say that
over there has been completely ruled out. Scientists continue to find evidence that suggest that
could be or could have been possible on
Moon of Jupiter. Eighth closest moon to
Jupiter, third of the Galilean satellites
Diameter: 5,262 kilometres / 3,270 miles
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
which orbits the Solar System's largest planet,
. Large enough to have been spotted by Galileo Galilei in 1610 through one of the first telescopes,
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.
Moon of Saturn. Twenty-first moon in orbit of
Diameter: 5,510 kilometres / 3,200 miles
The tenth largest object in the Solar System is
, the Solar System's second largest moon which orbits the Solar System's second largest planet,
. 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
as water does on Earth
. Scientists sometimes consider
to be similar to an early
and some even consider the possibility of life there.
Inner Planet. Closest planet to the Sun
Diameter: 4,878 kilometres / 3,031 miles
Because we're no longer allowed to call
a planet, the final planet to feature in our chart, and therefore the smallest, is
. Whizzing around the Sun
in just 88 days,
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's surface is heavily cratered, although hidden in the shadows of some of the craters at its poles is a secret stash of water. Well, it was a secret until it was found. It's likely the water came from a comet.
Moon of Jupiter. Ninth closest moon to
Jupiter, fourth of the Galilean satellites
Diameter: 4,821 kilometres / 2,996 miles
It's back to Jupiter
for now with
occupying twelfth spot in our list.
is the fourth of the Galilean satellites
four largest moons discovered by Galilei in 1610.
is heavily cratered like most moons, but the rings around its craters appear quite bright suggesting that ice may be under its surface.
Moon of Jupiter. Fifth closest moon to
Jupiter, first of the Galilean satellites
Diameter: 3,643 kilometres / 2,264 miles
, it's off the Jupiter
we go - again. The thirteenth largest object in the Solar System is
third largest moon and the closest of the four large
to orbit the planet.
is a violent world where volcanoes erupt on a daily basis. The insides of
are constantly churned and heated by the gravitational tug-of-war between
on one side and Europa
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
isn't the only only geologically active place in the Solar System, a discovery that undoubtedly excited many scientists.
Natural satellite. In orbit of Earth
Diameter: 3,475 kilometres / 2,159 miles
Next up is a very familiar face -
, or Luna if you want to give it another name. Thought to have formed out of the debris from a collision of a planet-sized object with
in the early days of the Solar System, the
is 400 times smaller than the Sun
but, by some bizarre coincidence, is 400 times closer to
than the Sun
. This means that the
and the Sun
appear to be the same size from
and that the Moon
can completely cover the
disc during a total eclipse
is the only surface other than
to have been stepped on by human beings. The last one there stepped off it in 1972 but it's hoped that
humans will return to its surface in 2024.
Moon of Jupiter. Sixth closest moon to
Jupiter, second of the Galilean satellites
Diameter: 3,122 kilometres / 1,940 miles
It's back to Jupiter
for the final time, and time to acquaint ourselves with
. 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
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
oceans? Not me, that's for sure.
Moon of Neptune, seventh closest to the planet
Diameter: 2,707 kilometres / 1,680 miles
It's over to Neptune
now as its largest moon,
, takes sixteenth spot on our list.
is a cold, lonely place (well, I suppose everywhere other than
is lonely), so to pass the time and amuse itself,
orbits backwards and sometimes emits gasses. Nitrogen gas escapes through geysers in a similar, but less exciting, way to the volcanoes on
. What this proves is that even distant moons are geologically active.
Dwarf planet/Trans-Neptunian Object/Kuiper Belt Object/Plutoid. Usually orbits beyond Neptune
Diameter: 2,370 kilometres / 1,473 miles
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. Pluto was once considered to be the ninth planet in the Solar System but was reclassified in 2006 as a dwarf planet following the discovery of Eris a few years earlier. For a while it was thought that Eris was actually larger than Pluto, but a recent remeasurement reveals that it wasn't. Good news for Pluto, bad news for me as I've had to shuffle this chart around.
Dwarf planet/Trans-Neptunian Object/Kuiper Belt Object/Plutoid. Most distant dwarf planet in Solar System
Diameter: 2,326 kilometres / 1,445 miles
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 poor old Pluto, which lost its status as a planet.
Moon of Uranus, seventeenth closest moon to
Diameter: 1,578 kilometres / 982 miles
Titania is a moon of Uranus
and the largest moon to orbit the planet. It
was discovered by William Herschel, the astronomer who discovered
and another of its
moons. That other moon is Oberon
, which would be the 21st object on this list. Not a lot is known about Titania. It is half ice and half rock and orbits above and below
due to Uranus
travelling around the
on its side.
Moon of Saturn, twentieth closest moon to the
Diameter: 1,530 kilometres / 949 miles
Taking last spot in our list of the Solar System's largest objects is Rhea, the second largest moon of
. 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."