From Pluto to Uranus, Venus to Mars, we now know more about the planets in our solar system than ever. But do you know why the planets are called what they’re called?
For 4.6 billion years, the planets of our solar system have moved in silent orbit around the Sun.
Closest to the Sun are the four inner planets, Mercury, Venus, Earth and Mars. Each of them is relatively small and is made of rock and metal. Beyond the inner planets are the four outer planets, Jupiter, Saturn, Uranus and Neptune.
These are made of gases like hydrogen and helium (any aliens on these planets presumably have squeaky voices). Scattered among them are the dwarf planets Pluto, Ceres, Eris, Makemake and Haumea. These are objects bigger than asteroids and comets, but smaller than planets.
Some of these planets and dwarf planets can be seen from Earth, even with the naked eye. We know more about them now than we ever have in history. But do you know where the planets get their names?
The inner planets
The glare from the Sun means Mercury can only be seen in twilight. When that first happened no one knows, but the first recorded sighting of Mercury was in 265BC by an ancient Greek philosopher called Timocharis. But it was the Romans who named the planet. The planet is the fastest to move around the Sun. And so the Romans called it Mercury, after the messenger god who can run very quickly because he has winged shoes. Or possibly winged sandals.
Venus is the brightest object in the night sky. People have been observing it for thousands of years. And it was because it shines so brightly that it was called Venus. Venus was the Roman goddess of love, sex and desire. She was also the most beautiful of all Roman goddesses, and as such, her name was given to the most beautiful of all the stars.
Welcome home! The word Earth comes from the Old English, eorthe which means ground. Many other languages use their equivalent word for ground as a name for our planet. Like terre in French, tierra in Spanish, земля (zemlya) in Russian. But more ancient cultures used a variety of names for the planet. In Aztec culture, for instance, the Earth was called Tonantzin, which means simply ‘our mother’. And yet, the Earth does have a proper name, too. We just don’t use it very much. In Roman times, astronomers called the Earth Gaia. In mythology, Gaia was the great mother of all the gods and all the stars. Oh, and while we’re talking about the Earth’s name, ancient astronomers also had a proper name for the moon. The word ‘moon’ can mean anything orbiting a planet – Jupiter has 64 moons, for example. The Greeks called our moon is Selene. She was the sister of the ancient Greek Sun god, Hyperion. And the Romans called the moon Luna, after the sister of their Sun god, Apollo.
Even thousands of years ago, ancient astronomers could see the planet Mars’ red colour. The ancient Babylonians called the planet Nergal, after their god of fire. And then the Romans came along. For them, the red colour of the planet came to be associated with blood and death. And that’s how the planet was named after Mars, the Roman god of war. Interestingly, in mythology Mars and Venus were said to be lovers and Mars’ two moons are named after the two children that came out of that liaison, Phobos and Deimos. Phobos became the god of fear, and Deimos the god of terror. Which is appropriate, considering they are in the constant orbit of war. Poor old Venus doesn’t have any moons at all. And neither does Mercury, for that matter.
The outer planets
Lots of the planets were named by the Romans. That’s because at the time when many advances in astronomy were being made, the Roman Empire held great influence over vast swathes of the known world. Jupiter was no exception. Jupiter is massive. Eleven times bigger than our planet, Gaia. And so, the Romans named the planet after Jupiter, the king of gods. He was also god of thunder. Which is appropriate because there are often storms on planet Jupiter. These are storms that last several hundreds of years, cover thousands of kilometers and whip up winds that can reach 360kph.
Way back when, people believed the Sun and the planets orbited around the Earth (Gaia), which they believed to be stationary. As such, the Romans called the planets planetes asteres, or wondering stars. The slowest of these wondering stars took a whole 30 years to complete its orbit. And that’s why they called it Saturn, after the god of time. Saturn’s seven rings, which were discovered over a long period of time starting in 1610, were named, rather unimaginatively, A, B, C, D, E, F, and G. But Saturn’s moons, of which there are 52, the most recent of which was discovered in 1981, are grouped and named after gods from many ancient cultures including Inuit, Norse and Gallic.
A giant planet made of gas and ice, Uranus cannot be seen from Gaia without a telescope. So the people of the ancient world had no idea it existed. It wasn’t discovered until 1781, and at first it was called George. Yes. You have read that correctly. A planet 47,000kms across and with 27 moons was once called George, in honour of King George III of England. But pretty soon, everyone realised this was silly. So the planet was named Uranus, after the Greek god of the sky who was, incidentally, the lover of Gaia. In fact, Gaia turned out to be something of a thorn in the side of Uranus. Legend has it Gaia bore Uranus several children, but Uranus didn’t like any of them. His least favourite was Tartarus, who he imprisoned in the bowels of the earth. To punish Uranus, Gaia gave her other son Cronus a blade made of flint and urged him to castrate his father. This Cronus did before hurling Uranus’s disembodied testicles into the sea.
Neptune is a planet made up of gas and ice. Like Uranus. And when it was first seen through a telescope on planet Gaia in 1846, scientists were struck by its colour. Blue. A brilliant blue. Neptune is blue because the gas it’s mostly comprised of is methane. Methane absorbs the red light from the sun, and reflects the blue light back into space. And as the planet appears blue, it was named after the Roman god of the sea. Neptune was depicted in Roman art with blue eyes and green hair. And usually, a very muscly body. The planet has 14 moons, all of which have been named after gods and goddesses associated with water. The largest is Triton, named after the sea messenger god, Triton. Triton was a merman, human to the waist and fish below it. Bizarrely, the moon orbits Neptune backwards.
The dwarf planets
Pluto is one of the coldest places you can imagine. -375 degrees on a warm day. So when it was discovered in 1930, it was named after the Roman god of the Underworld. In Christian tradition, the Underworld, or Hell, is a hot pit of fire and brimstone. But for the ancient Romans, the Underworld, where the dead were taken if they’d not lead good lives, was a place of ice and bone-chilling winds. Naming the freezing cold dwarf planet after the god of the freezing cold Underworld makes perfect sense. Pluto’s biggest moon is Charon. In mythology, Charon is the ferryman who would take the souls of the dead into the Underworld on his special boat. Except sometimes, he’d take the living there, too. If they’d deserved it.
The smallest of all the dwarf planets, Ceres is only 950km across. Which is about the same length as the UK (1,000km). It’s the closest of the dwarf planets to the Sun, and the only one in the inner solar system. Scientists reckon there’s an ocean on Ceres, and that it might possibly be able to support life as we know it. It was discovered in 1801, and was named after Ceres, the Roman goddess of agriculture. Cereal is another word we get from Ceres. Interestingly, Ceres was the wife and the sister of Jupiter. And she didn’t like pigs, because they’d dig up the crops under her protection. Sadly, it’s unknown what she thought of bacon sandwiches!
Eris is the biggest of the dwarf planets. It’s 28% bigger than Pluto. As such, when it was discovered in 2005, there was much debate other whether it should actually be considered a planet or a dwarf planet. And it’s out of that debate that Eris’s name was chosen. Eris was the Greek goddess of discord, arguments and strife. Because Eris was always causing arguments, none of the other gods liked her very much. So when two of them were getting married, they deliberately left Eris off the guest-list. Needless to say, Eris was not happy about this. But she got her revenge. When the wedding party was in full swing, she tossed an apple in through an open window. Tied to the apple was a message. It said, This apple is for the most beautiful person at the party. And, of course, an argument erupted over which of the wedding guests was the most beautiful. The goddesses Hera, Athena and Aphrodite all thought they were the most beautiful. A third party was called to judge. Prince Paris of Troy. Cunning Aphrodite managed to bribe Paris into saying she was the most beautiful by promising him the love of the most gorgeous human being, Helen of Troy. And this sparked the chain of events that resulted in the Trojan War. So Eris really did get her revenge, and then some!
Don’t make the mistake of pronouncing this make-make. It should be mah-KEH-mah-KEH. Like Ceres, it’s another tiny world. But unlike Ceres, it’s in the outer reaches of the solar system. It was discovered only in 2005. And here’s a first; it wasn’t named after a Roman or Greek god. It was named after a Polynesian god. In the mythology of Easter Island, Makemake is the creator of humanity and the god of fertility. He had a man’s body and a bird’s head. And because of the connection with Easter Island, some scientists jokingly call the dwarf planet Makemake the Easter Bunny. Music fans may recognise the name, too. The Austrian band The Makemakes named themselves after the Easter Bunny. But sadly, failed to get any points at all when they represented Austria at the Eurovision Song Contest 2015.
A day on Haumea lasts just four hours. And this dwarf planet is egg-shaped. An astral Humpty-Dumpty. It was discovered in 2004 and named Haumea after the Hawaiian goddess of fertility. Lots of astronomy is done on the island of Hawaii because of its elevation and clear skies. In Hawaiian mythology, Haumea’s children sprang from different parts of her body. The same thing happened with the dwarf planet Haumea. A long time ago, it was hit by an asteroid. In the impact, parts of the planet were blasted off, but the debris from this impact formed Haumea’s two moons. These two moons are named after the goddess Haumea’s two daughters, Hi’iaka and Namaka.