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24 Fascinating Facts About the Solar System

Here are 24 out-of-this-world facts about the corner of space that’s home to Earth.

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The solar system: It’s big, it’s heliocentric, and it’s got space junk to spare. Here are 24 out-of-this-world facts about the corner of space that’s home to Earth, enough asteroids to keep Ben Affleck and Bruce Willis working for decades, and a football-shaped dwarf planet called Haumea, adapted from an episode of The List Show on YouTube.

1. Our solar system is a group of celestial bodies in the Milky Way galaxy.

At its center is a 4.5 billion-year-old star, a.k.a. our sun, that is orbited by eight planets, over 150 moons, and millions of meteoroids, comets, and asteroids, plus a few dwarf planets. Which sounds impressive, but it’s just one of tens of billions of solar systems that scientists estimate can be found within the Milky Way.

2. The sun is huge.

If you combined the mass of everything in the solar system, the sun would account for more than 99 percent of that mass.

3. Mercury is shrinking.

Like Earth, Mercury experiences tectonic activity. Pictures taken of the planet have indicated that the surface is changing. The planet has a solid inner core that’s surrounded by a liquid metal outer core, which is in the process of cooling. Every rocky planet is still cooling from when they initially emerged. And as the liquid parts of Mercury’s core become solid, there’s contraction, leading to land shifting and a smaller planet overall.

4. A block of lead on Venus would melt like a block of ice on earth.

The surface temperature on the second planet from the sun is around 900°F. Even spacecraft that get sent to Venus aren’t able to withstand the environment for long. The Soviet Union’s Venera 13 craft, for example, landed on Venus in 1982 and lasted about two hours. Before its demise, though, Venera was able to send back the first color pictures of the planet and analyze some of its soil.

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5. Rocks from space have been found all over planet Earth.

In 1996, for example, geologist Aly Barakat found one in the Sahara Desert. It was dubbed the “ Hypatia stone” and its unique chemical composition has been studied extensively. Geologists have never seen anything like it, even in meteorites or other planets. In 2018, researchers hypothesized that the Hypatia stone is older than our solar system. It contains elements you learned about in chemistry class, like nickel, phosphorus, carbon, iron, aluminum, and silicon. But they're part of compounds that are unique, or appear together in odd ways. As one of the authors of that research explained to Popular Mechanics, "We think that many compounds (polyaromatic hydrocarbons, silicon carbide, nickel phosphide compound, native metal inclusions) are presolar. The assembly probably occurred in the early solar nebula."

6. Jupiter is massive.

It’s large enough to fit all the rest of the planets inside it. Or put another way: It would take 1300 Earths to fill up the inside of Jupiter.

7. Jupiter's red spot changes in size.

Even Jupiter’s red spot is larger than Earth—sometimes. The red spot is a storm containing winds up to 400 mph that heats the atmosphere above it to 2400°F, and its size isn’t constant.

8. The dwarf planet Eris was indirectly responsible for Pluto’s demotion to a dwarf planet.

Eris, discovered in 2005, is comparable in size to Pluto, which threw astronomers into a tizzy—they worried about how many newly discovered bodies orbiting the sun might have to be considered planets. After Eris’s discovery, the International Astronomical Union created new planet standards: "To be considered a planet now, a celestial body must be round, orbit the sun, and clear its orbit of smaller objects."

9. Another dwarf planet named Haumea was found around the time Eris was discovered.

Haumea is a weird-looking rock; it spins so fast that it’s shaped like a “football” or “plump cigar,” as NASA describes it. Haumea completes a rotation in under four hours.

10. Space junk is a big problem.

Between meteoroids and debris created by humans, NASA knows of over 20,000 pieces of " space junk" bigger than a softball orbiting the Earth. And that's of 500,000 total pieces they track, all of which is the size of a marble or larger. There are millions of pieces so small that it’s not possible to track them. According to the agency, man-made space junk includes "nonfunctional spacecraft, abandoned launch vehicle stages, mission-related debris and fragmentation debris."

11. Space junk can move at more than 17,500 mph.

That means that even something as small as a chip of paint can do damage to operational spacecraft—sometimes, the International Space Station has to maneuver to get out of the way of space junk.

12. Space junk might cause Kessler Syndrome.

Beyond the danger to spacecraft, some scientists are worried about Kessler Syndrome, when there’s so much junk in low-Earth orbit that it all starts smashing together, creating more debris. Think of it like the domino effect, but in space.

The European Space Agency has proposed cleaning space junk up via nets. A team at Texas A&M University has suggested sending a mechanism to space that would push the objects into Earth's atmosphere, where it would burn up, then use the momentum from the thrusts to travel from debris to debris.

13. One object in our solar system orbits the Sun backwards.

In 2008, astronomers discovered an object that orbits the sun at about a 104-degree tilt. Technically, this means that the 30-mile-wide object is orbiting backwards. The team that found it gave it the name Drac, based on the myth that Dracula could walk up walls.

14. Drac was found in the Kuiper Belt.

The Kuiper Belt is an area of our solar system past Neptune containing a lot of icy objects; it's also where Pluto is located.

15. Neptune has a moon that’s a lot like Pluto.

Triton is probably one of those icy Kuiper Belt objects that at some point got trapped by Neptune’s gravity and has been orbiting it ever since. Triton has a couple other distinctive features: It orbits Neptune in the opposite direction than the planet is rotating, and it has geysers that erupt.

16. Mercury retrograde is all about perspective.

There’s no proof connecting what the planets do with the goings-on of humans, but people have been blaming Mercury retrograde for their problems since around the late 19th century. When Mercury is in retrograde, it looks like it’s moving backwards to people on Earth. This is just a perspective issue. Mercury takes 88 Earth days to rotate the sun, whereas Earth takes 365. So as Mercury passes us, in between Earth and the sun, it appears to go backwards. It’s like when you’re driving fast and a car next to you looks like it’s going backwards or slowing down.

17. Pluto probably wasn't named after Pluto the Disney character.

Some claim that Pluto was named after the Walt Disney dog who appeared in 1930, the same year the dwarf planet was discovered. But in the 1930 film  The Picnic, the character was called Rover. The dog wasn't known as Pluto until 1931, the year after the naming of the planet. Still, there’s a fun little coincidence that links Pluto the dog and Pluto the planet: In 2015, NASA released new photos of the planet, which revealed a light area that some said looked like an image of the dog’s head.

18. One dwarf planet in our solar system has also been a planet and an asteroid.

Pluto’s fellow dwarf planet Ceres takes up about 25 percent of the mass of the main asteroid belt, which is located between Mars and Jupiter. In the 19th century, Ceres was considered a planet. Then it was demoted to asteroid. Finally, in 2006, it was upgraded to dwarf planet.

19. There are millions of asteroids in the main asteroid belt between Mars and Jupiter.

They can range from less than 33 feet (10 meters) to 329 miles (530 kilometers) long. But NASA keeps an ongoing list of asteroids with the potential to hit Earth in the next century along with the probabilities of that happening. They’re keeping a list because they don’t wanna miss a thing … and by a thing, we mean an asteroid.

20. Two of Saturn's moon have water.

Saturn's moon Enceladus has an entire ocean made up of salt water. In 2018, researchers found complex organic molecules on Enceladus, which is a sign that it potentially could contain life—or not. That’s why there are proposals to send a mission there to find out.

Saturn has a second moon with water: Titan, which also has carbon-containing chemicals, another promising sign for life. Any place that has both water and carbon-containing chemicals is tantalizing to researchers looking for life in other places out in space.

21. From an Earthling's perspective, Mars has pretty extreme temperatures.

Compared to Earth’s average temperature of 57°F, Mars is at -81°F. At the poles, a temperature of -225°F degrees is possible. There also has been no rain on the planet for millions of years.

22. The tallest volcano we know of is on Mars.

Olympus Mons is estimated to be 16 miles tall, meaning it’s basically three Mount Everests. It probably formed around 350 million years ago, but it last erupted as recently as 2 million years ago.

23. We have billions of comets in our solar system.

They're mostly in the Kuiper Belt and Oort Cloud. A comet is made of ice and rock until it gets close enough to the sun that the exterior turns into a cloud of gas and dust. That’s when the distinctive tail forms. In 2014, a probe landed on a comet for the first time. Here’s one interesting piece of information gathered from that mission: Due to the chemistry of its surface, a comet smells like cat pee, rotten eggs, and bitter almonds. So maybe think twice before picking up any comet-scented candles.

24. Many of these facts would still be unknown if not for space exploration.

Take the Cassini spacecraft, which launched in 1997 and didn’t stop collecting data until 2017. In those 20 years, it traveled 4.9 billion miles and completed 2.5 million commands. Most of that time was spent around Saturn—doing everything from taking pictures to gathering data to analyzing samples. It sampled Saturn’s atmosphere and nearby dust grains, and was even the first to take a sample of an ocean in outer space (the one on Enceladus). Cassini was  sent into Saturn’s atmosphere to disintegrate on September 15, 2017. At a press conference, Cassini’s program manager Earl Maize said, “To the very end, the spacecraft did everything we asked.”

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This post originally appeared on Mental Floss and was published June 8, 2023. This article is republished here with permission.

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