solar system facts, inner planets, outer planets

Solar System Facts: Get to Know Your Stellar Neighborhood

Read Time: 8 minutes

Have you ever looked up at the sky and wondered what was out there? You’re not alone — humans have been wondering what exists outside our atmosphere for centuries. Before you start dreaming of far-away galaxies and planets that might hold intelligent life, let’s take a look at our closest stellar neighbors. Here are some fantastic solar system facts that you might not have known.

The Sun

The sun is the core of our solar system. This yellow star is roughly 4.6 billion years old and was formed when a gas cloud spun fast enough to flatten out, drawing enough stellar material into the center of the cloud to ignite and build the star that we now call our sun.

The star itself is large enough that more than a million planets the size of Earth could easily fit inside it — although they’d burn up long before they reached the interior of the sun. The core of the sun reaches temperatures higher than 27 million degrees F, or 15 million degrees C. The surface is a bit cooler, sitting at about 10,000 degrees F, or 5,500 degrees C.

At this point in its life cycle, the sun is currently a yellow dwarf. As it gets older, it will start to run out of hydrogen to burn and will expand, becoming a red dwarf. This stage won’t occur for another 5 billion years, but if there are still humans on the Earth by then, they will need to evacuate. Eventually, it will shrug off its outer layers, becoming a small white dwarf, and then finally a black dwarf as it burns through its remaining fuel.

The Inner Planets

The inner planets are those closest to the sun: Mercury, Venus, Earth and Mars. This is the part of the solar system that we call home.

Mercury is the closest planet to the sun, named for the Roman messenger of the gods. It has a short year — 88 days to complete a full rotation around the planet, compared to our 365. However, it rotates so slowly that one day on Mercury is equivalent to 59 days here on Earth. The year is so fast that if you are 32 on Earth, you’d be 135 on Mercury. The planet has a thin atmosphere, but it’s so close to the sun that it’s too hot to support human life.

Venus is next, named for the Roman goddess of love. The days here are even longer on than on Mercury — it rotates so slowly that one day is 243 Earth days long. The atmosphere is both thick and caustic, and during the day the surface temperature can reach more than 900 degrees F. If you’re 32 on Earth, you’d be 52 on Venus.

Earth is the third planet in our solar system, and it’s the planet we call home. Our planet is located in what we call the habitable zone. It’s the perfect distance from the sun, so the surface isn’t too hot, but we also don’t freeze.

The last inner planet is Mars, named for the Roman god of war. This red planet has a thin atmosphere and is much colder than Earth due to its distance from the sun. A year on Mars is nearly twice what it would be on Earth, even though the days are similar in length. A 32-year-old would only be 17 on Mars — not yet old enough to vote!

solar system facts, asteroid belt
This diagram shows a bird eye view of our asteroid belt, which lies between the orbits of Mars red and Jupiter purple. Image Source and Caption Credit: NASA

The Asteroid Belt

The space between the inner and outer planets is home to nearly 2 million large asteroids and millions of smaller ones. Most are leftover pieces that were created when the inner rocky planets formed. There are three distinctly different types of asteroids in the belt: C, S and M-Type.

C-Type asteroids are the most common in the belt and are usually made up of things like clay and silicate rocks. They’re often dark-colored and considered the oldest things in the solar system.

S-Type asteroids consist of a combination of silicate materials and nickel-iron metals.

M-Type asteroids are metallic, composed of primarily of nickel-iron. They melted at some point, which caused the iron to sink into the center of the asteroid and basaltic stone to rise to the surface. Most of the asteroids are given number designations, but some receive names like Ceres, one of the largest asteroids in the belt. This celestial body also serves as the setting for the TV show “The Expanse.”


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The Outer Planets

This is where things start getting exciting. The outer planets are the ones that orbit out past the asteroid belt and make up the next section of our solar system. There are four outer planets: Jupiter, Saturn, Uranus and Neptune. Let’s take a look at some solar system facts about the outer planets.

Jupiter, named for the king of the Roman gods, is the largest planet in our solar system. It also has the most moons —79 identified to-date, with 12 discovered in 2018. This planet is known for its colorful exterior and its giant Red Spot, which is a massive storm that has churned the surface of the planet for hundreds of years. On Jupiter, because it has such a long orbit (4,332 days), a 32-year-old would only be 2 years old! Jupiter is currently orbited by a probe named Juno, which is the name of Jupiter’s wife in Roman mythology.

Saturn is another gas giant and exists in orbit past Jupiter. This planet gets its name from the father of Jupiter, also known as Chronos in Greek mythology. Saturn is iconic because of the massive rings — made of dust and ice chunks — circling its equator. We’ve since discovered that Saturn isn’t the only planet with rings, but until 1977, we couldn’t see any other rings on planets in our solar system. Saturn takes more than 10,000 days to complete an orbit around the sun, but a day on the planet is only about 10 and a half hours long. A 32-year-old on Earth would only be a little over 1-year-old on Saturn.

Uranus is the other planet in our solar system with rings. Its name is the Latin form of Ouranos, the father of the titan Chronos. It’s slightly larger than Neptune, but it has the smallest mass of any of the outer planets. Unlike all of the other planets in the solar system, Uranus rotates on its side. A single year on Uranus lasts 84 Earth years. Its odd rotation means that one side of the planet will experience 42 years — half of a year on Uranus — of sunlight while the other hemisphere experiences 42 years of complete darkness.

Neptune is the last outer planet, named for the Roman god of the sea. This planet is blue due to the methane in its atmosphere. It also has some of the fastest winds in the solar system. Winds in the atmosphere can reach more than 1,200 miles an hour. By comparison, the max speed of winds on Earth is 231 mph. One year on Neptune is nearly 165 Earth years.

solar system facts, Oort Cloud, Interstellar Space
This artist’s concept puts solar system distances in perspective. The scale bar is in astronomical units, with each set distance beyond 1 AU representing 10 times the previous distance. One AU is the distance from the sun to the Earth, which is about 93 million miles or 150 million kilometers. Neptune, the most distant planet from the sun, is about 30 AU. Informally, the term “solar system” is often used to mean the space out to the last planet. Scientific consensus, however, says the solar system goes out to the Oort Cloud, the source of the comets that swing by our sun on long time scales. Image and Image Caption Credit: NASA

The Trans-Neptunian Region

Finally, we have the Trans-Neptunian region of space. This region encompasses everything that exists beyond Neptune’s orbit, from the Kuiper Belt and the Oort Cloud to the dwarf planets: Pluto, Eris, Makemake, Haumea and Sedna.

The Kuiper Belt is a ring of ice chunks and dwarf planets that exist toward the outer edge of our solar system. We know of two dwarf planets within this belt: Pluto and Ultima Thule. However, it’s estimated that there are hundreds of thousands of icy planetoids or celestial bodies within the Kuiper belt and possibly a trillion or more comets.

Scientists previously considered Pluto the ninth planet of our solar system until 2006, when they downgraded it to a dwarf planet. This was the only rocky planet in the outer part of our solar system. The planet gets its name from the Roman God of the Underworld and has five moons. Charon bears the name of the ferryman in Greek Mythology that would carry souls across the river Styx. Following the theme, another moon, Styx, shares the name of that river. Nix, however, received its name from the Egyptian goddess of night and darkness, and Kerebos, for the three-headed dog that guards the entrance to the underworld. Finally, there is Hydra, named for the multi-headed serpent in Greek mythology.

Eris was discovered in 2005, named for the Greek goddess of discord and strife. Its moon Dysnomia, gets its name from the goddess’s daughter, the spirit of lawlessness. It’s about the same size as Pluto but has more mass and less ice than the other dwarf planet. One year on Eris takes 557 Earth years.

Haumea, a dawf planet shaped like a football,  received the name of the Hawaiian goddess of childbirth. Scientists discovered it in 2004. Water ice covers more than 75 percent of this dwarf planet’s surface.

Makemake has no moons, but appears to be covered in frozen methane. Scientists also discovered it in 2005.

Scientists discovered Sedna in 2003 and has an oddly oval-shaped orbit. Its strange orbit is makes it difficult to spot. Astronomers haven’t seen it since 2011.

Other dwarf planets are being discovered every day. In 2015, The Goblin was found, which at the time was the furthest dwarf planet in our solar system. Its orbit is so long that it takes more than 40,000 years to make one orbit of the sun. It orbits far beyond the Kuiper Belt.

The most exciting thing about The Goblin is the fact that it looks like the gravity of another large planet shaped it, meaning that there could be a ninth planet beyond the reach of our current telescopes. In 2018, the same team that spotted The Goblin found another planetoid even further from the Sun. Nicknamed Farout, it is even farther out in our solar system than the Oort Cloud.

The Oort Cloud is a sphere that surrounds our solar system. It primarily consists of ice chunks leftover after the formation of the outer planets. It, along with the Kuiper Belt, is the source of many of the comets we can see streaking across the night sky.

We live in an amazing space, and we’re learning more solar system facts with every passing year. Now, the next time you look up at the stars, you’ll have a better idea of what’s out there.

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Category: Space

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Article by: Megan Ray Nichols

Megan Ray Nichols is a freelance science writer and science enthusiast. Her favorite subjects include astronomy and the environment. Megan is also a regular contributor to The Naked Scientists, Thomas Insights, and Real Clear Science. When she isn't writing, Megan loves watching movies, hiking, and stargazing.