8 Astounding Facts About the Asteroid Belt

An artist's conception of the dwarf planet Ceres in the main asteroid belt.
An artist's conception of the dwarf planet Ceres in the main asteroid belt.
ESA/ATG medialab

The asteroid belt tells the story of the creation of the solar system. When it formed, not everything coalesced into a planet. Like LEGO bricks that never made it out of the bucket, these objects were organized by physics into a ring located between the orbits of Mars and Jupiter. This is the asteroid belt. Here are some things you might not know about it.


The asteroid belt in black and white.

Over a half-million asteroids have been discovered by scientists, with hundreds of thousands yet to be found. They are generally divided into three classes: S-type (for stony); C-type (chondrites, largely composed of carbon, the most common—and perhaps the oldest—of the bunch); and M-type (metallic). The asteroids range in length from 30 feet to 330 miles. For the most part, they are oddly shaped, and, like the planets, spin (though not always so eloquently). Some asteroids have moons; some have two. Not every asteroid is located in the asteroid belt. Some, called Trojans, share the orbit of Jupiter. Some lurk perilously close to Earth. These are called near-Earth asteroids.


A night sky with a shooting star.

The first asteroid was discovered in 1801 by Giuseppe Piazzi, though he didn't know it at the time. He thought he had discovered the long-sought planet between Mars and Jupiter. He named his discovery Ceres, after the Roman goddess of harvest (and namesake to the word cereal, though that word wouldn't be coined until 1818).

Just over a year later, another "planet" was discovered. And another. And another. Eventually, there were so many planets that astronomers threw up their hands and gave the whole group a new classification: asteroid, or "star-like" in Greek. The name was chosen because they appeared, well, star-like in telescopes; they would not resolve as discs as planets do. Ceres's run as a planet lasted about 60 years before it was demoted to asteroid. In 2006, the International Astronomical Union reclassified it again, this time as a dwarf planet. This is the same decision that designated Pluto as a dwarf planet, though there is some debate on this point.


An artists' rendering of the asteroid belt.

It's likely that illustrations you've seen of the asteroid belt are not drawn to scale. If all of the objects in the asteroid belt were brought together and made into a single ball, its combined mass would only be 4 percent of the size of the Moon. In fact, Ceres alone accounts for one-third of the total mass of the asteroid belt. 


A little girl plays with a toy rocketship in a space system.

What’s the biggest misconception that people have about the asteroid belt? Mental Floss asked Dante Lauretta, the principal investigator of the OSIRIS-REx mission to the asteroid Bennu (which once lived in the main asteroid belt before being jarred loose by Saturn and sent on a course for the inner solar system). His response: The Empire Strikes Back. People imagine "that it's this tumbling, highly energetic boulder field with things crashing into each other constantly, and Han Solo has to dodge and weave to avoid collisions," Lauretta says.

But the asteroid belt is downright spacious. If the arcade game Asteroids were real, it would pretty much consist of a ship and a black screen and … nothing to shoot. "When you fly a spacecraft through the asteroid belt, it’s a real challenge to actually get close enough to an asteroid to see it," Lauretta explains. "You have to specifically target it." There are, on average, 620,000–1.8 million miles between asteroids.


An artist's concept of the solar system.

Back in the 1980s, scientists really set about spectrally classifying each object in the asteroid belt, and they discovered a compositional gradient. There were a lot of dark, carbonaceous objects in the outer asteroid belt, and brighter, "ordinary chondritic," S-type material in the inner asteroid belt. Spectral surveys today are starting to get really detailed, and scientists are getting a good look at objects as small as 6 miles across. As they get into asteroid compositions, they are discovering a fine structure in the compositional pattern, and placing it in the context of the dynamic state of the early solar system.

"Organics and ices are going to be stable farther out [in the belt], and metals and rocks are going to be stable farther in. You expect to see that," says Lauretta. "But now you're starting to see that there really are organic-rich and water-rich materials in the main belt. It's a small fraction of it, but it's a significant fraction. And there's rocky and bright material in the outer belt." That distribution of material is a record of migration of giant planets and the dynamical evolution of the solar system.

"I think we're going to be able to piece together a much more complex, chemical-dynamical coupled model of the evolution of the solar system, and see it almost like the stratigraphic layers of the geologic record. It will tell us the story of the evolution of the belt—not just the initial protoplanetary disk which established that chemistry, but how major events in the evolution of our solar system modified that distribution."


An asteroid in space.

Presently, planetary scientists are trying to identify and understand the primordial structures in the asteroid belt much in the same way that paleontologists or geologists search for the earliest signs of the origin of life in the geologic record. "That's where the biggest challenge lies," says Lauretta. "There is, in the most ancient examples, a discrete signal that you've got to pull out. It's going to be very tiny."

Scientists endeavor to understand what has been preserved from the dawn of the solar system—what they can trust as a true primordial signature of how our planetary system formed—versus what has been eroded or modified or changed over 4.5 billion years of evolution. "Trying to pick out that starting condition and targeting our scientific investigations into those areas is where the greatest challenge lies."

NASA's recently announced Lucy mission to multiple asteroids will help do this. "Everybody thinks those Trojans are the ones that hold that key to the earliest, most primitive material of the solar system," says Lauretta. "The Lucy team can get out there and do some cool science."


A snowflake in snow on a dark background.

No two are exactly alike, and each one has its own story to tell. "Every asteroid is a unique world to explore, and that is awesome," says Lauretta. "There is so much diversity and so many challenges out there. When we truly get out there and start poking around, we're going to see some stuff happening that we never even dreamed of."


An artist's drawing of Dawn firing its engines above Ceres.

NASA's Dawn spacecraft is currently in orbit around Ceres, where it continues to characterize that object and how it changes as it circles the Sun. (It previously orbited Vesta, making it the only spacecraft to orbit two extraterrestrial bodies.) NASA's OSIRIS-REx will arrive at the asteroid Bennu in August 2018. Earlier this year, the agency approved two missions to small bodies: the spacecraft Psyche will travel to the asteroid 16 Psyche, a mysterious, all-metal world. (It might once have been the core of a protoplanet.) The Lucy mission will travel to five Trojan asteroids that share Jupiter's orbit. The Japanese Space Agency's Hayabusa 2 spacecraft will arrive next year at Ryugu (a.k.a. 1999 JU3), a near-Earth asteroid. Like OSIRIS-REx, it will take a sample and return it to Earth for analysis.

And that analysis is serious business. In the case of samples and meteorites, Lauretta says, "most people don't realize that we pick apart these things grain by grain, atom by atom, isotope ratio by isotope ratio, and put together detailed stories about what happened billions of years ago in our solar system."

This Cool T-Shirt Shows Every Object Brought on the Apollo 11 Mission

Fringe Focus
Fringe Focus

NASA launched the Apollo 11 mission on July 16, 1969, ending the space race and beginning a new era of international space exploration. Just in time for the mission's 50th anniversary this year, Fringe Focus is selling a t-shirt that displays every item the Apollo 11 astronauts brought with them to the Moon.

The design, by artist Rob Loukotka, features some of the iconic objects from the mission, such as a space suit and helmet, as well as the cargo that never made it to primetime. Detailed illustrations of freeze-dried meals, toiletries, and maintenance kits are included on the shirt. The artist looked at 200 objects and chose to represent some similar items with one drawing, ending up with 69 pictures in total.

The unisex shirt is made from lightweight cotton, and comes in seven sizes ranging from small to 4XL. It's available in black heather or heather midnight navy for $29.

If you really like the design, the artwork is available in other forms. The same illustration has also been made into poster with captions indicating which pictures represent multiple items of a similar nature.

The International Space Station Will Start Accepting Visitors … For $58 Million


If you've ever wanted to visit the International Space Station, your chance is coming soon—assuming you have a few million set aside. Recently, NASA announced that this orbiting outpost will be open to private citizens starting in 2020.

However, it won't be cheap. According to The Denver Post, each trip could last up to 30 days, and NASA estimates the cost of a round trip at $58 million, as well as an additional $35,000 charge per night. And, it's not just for kicks—you need to have a mission of your own. The space agency is allowing companies that want to conduct commercial or marketing work to send employees to the ISS as long as they meet one of the three requirements:

  • require the unique microgravity environment to enable manufacturing, production, or development of a commercial application;
  • have a connection to NASA's mission; or
  • support the development of a sustainable low-Earth orbit economy

The space station had a visitor back in 2001—Californian businessman Dennis Titobecame history's first space tourist when he spent a week aboard the ISS with two Russian cosmonauts who took him out there on a Russian spacecraft—but this would be a first for NASA. The agency was opposed to training and flying with Tito back in 2001; at the time, NASA administrator Daniel Goldin said, "Space is dangerous. It's not a joyride. Space is not about egos."

Now, NASA is ready to open the shuttle doors to private citizens. In addition to U.S. citizens, those from other countries are eligible to travel as long as they fly on a U.S.-operated rocket. These lucky private astronauts will have to go through the same medical checks, physical training, and certification procedures as crew members before traveling—a process that could take up to two years.

Along with this exciting news, NASA has bigger plans in mind. They are considering the possibility of a private sector company eventually taking control of the station and paying for its expensive upkeep. NASA has yet to announce when this transition would take place, but said in a statement that the "ultimate goal in low-Earth orbit is to partner with industry to achieve a strong ecosystem in which NASA is one of many customers purchasing services and capabilities at lower cost."

In addition, they hope that the revenue will assist in the operational costs for NASA's Artemis program, which is focused on sending astronauts—including the first woman—to the Moon by 2024.

[h/t The Denver Post]