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."

The Geminid Meteor Shower Peaks This Week: Here's When and Where to See It


Star-gazers are in for a treat this week with the Geminid meteor shower set to light up skies across the globe. According to Space.com, the shower produces consistently stunning light shows this time each year, with meteors that are fast, frequent, and bright depending on where they're viewed. Whether you catch the spectacle every December or you'll be watching it for the first time, there's some important information to know before the 2018 event.

While most meteor showers are the product of our planet passing through the tail of a comet, the Geminid meteors come from something different: A small, rocky asteroid called 3200 Phaethon that leaves a wake of fiery debris like a comet. Its orbit brings it very close to the Sun, and when this happens, bits of rock break off in the heat and trail the object through space. (Some astronomers refer to 3200 Phaethon as a "rock comet.")

When the Earth passes through the tail, the debris burns up in the atmosphere, producing a bright show that's visible from the ground. And because the matter that trails 3200 Phaethon is denser than what you'd find behind a comet, it takes longer to burn up, creating a brighter spark and sometimes breaking up into multiple meteorites. This year viewers can expect to see more than one meteor a minute with up to 100 meteors per hour at the shower's peak.

The shower peaks the night of Thursday, December 13 and early Friday morning on December 14. The best time to watch is when the skies are darkest, usually around 2 a.m. local time. Unlike two years ago, when the Geminids coincided with a supermoon, the Moon will set around midnight on Thursday so viewing conditions will be ideal.

The Geminid meteor shower is visible around the world, though it's most prominent in the northern hemisphere. As is the case with all celestial events, people who live as far away from cities as possible will get the best view, but even people watching from the suburbs could catch as many as 30 meteors an hour.

[h/t Space.com]

Did NASA Ever Consider Women for the Mercury, Gemini, or Apollo Programs?

Russell L. Schweickart, Keystone/Getty Images
Russell L. Schweickart, Keystone/Getty Images

C Stuart Hardwick:

Unambiguously, no.

This was not sexism. NASA decided early on, and quite correctly, that early astronauts must all be experienced high-performance jet test pilots. To anyone who understands what the early space program involved, there can be little question that choosing all men was the right call. That's because there were zero women in the country with high-performance test flight experience—which was due to sexism.

You may have heard of the so-called “Mercury 13” or the Women in Space Program, both of which are misleading monikers invented by the press and/or American aviator Jerrie Cobb.

Here’s what happened:

Randy Lovelace’s laboratory tested astronaut candidates to help NASA select the initial seven Mercury astronauts. He later ran Jerrie Cobb through the same Phase I (biomedical) tests (though not through the other tests, as he didn’t have access to equipment owned by the military). Contrary to some reports, Cobb did not test superior to the men overall, but she did test as well overall. And while that should not have been a surprise to anyone, it was in fact a surprise to many.

Lovelace published a paper on the work in which he suggested that women might actually be preferable candidates for space travel since they weigh less on average and consume less oxygen, water, and other consumables, a fact which I exploited in my book, For All Mankind, and I can tell you that on a long duration mission (of several months) the difference really does add up.

This had no effect on Mercury, Gemini, or Apollo, all of which were short little jaunts in which the mass of the astronauts wasn’t terribly critical, and all of which were always going to be flown by high-performance test pilots anyway.

However, it attracted the attention of famed aviation pioneer Jackie Cochran, who agreed to fund further research on the suitability of women for space.

Pioneer American aviator Jacqueline "Jackie" Cochran in the cockpit of a Curtiss P-40 Warhawk fighter plane
Jackie Cochran in the cockpit of a Curtiss P-40 Warhawk fighter plane
Public Domain, Wikimedia Commons

Cochran and Cobb recruited several more women, mostly from the ranks of the Ninety-Nines, a women aviator’s professional organization founded by Amelia Earhart. These women also went through the initial biomedical testing, and 13 passed at the same standard as met by the Mercury astronauts.

So far so good. Cobb, Rhea Hurrle, and Wally Funk went to Oklahoma City for an isolation tank test and psychological evaluations, and Lovelace secured verbal agreement through his contacts to send another group to the Naval School of Aviation Medicine for advanced aeromedical examinations using military equipment and jet aircraft.

However, no one had authorized the use of the military facilities for this purpose—or the costs that it would entail. Since there was no NASA request behind this effort, once Lovelace tried to move forward, the military refused his access.

Meanwhile, Cobb had been enjoying the attention she was receiving and, according to some, had gotten it into her head that all of this was going to lead to some of the women actually flying in space. In fact, I’ve found no evidence that Lovelace ever implied that. This was a small program of scientific study, nothing more. Nevertheless, Cobb flew to Washington, D.C. along with Jane Hart and was given a meeting with then-vice president Lyndon Johnson.

Johnson was congenial—Cobb has always claimed he pledged his support—but immediately afterward, he sent word to have all support for the experiments withdrawn.

Far be it from me to defend the motives of LBJ, but consider this: The president had publicly committed the nation to returning a crew from the moon by the end of the decade—and this was at right about the same time when enough work had been done for Johnson to have a handle on just how hard that was going to be. He may or may not have supported the idea of women astronauts in general—we have no idea—but Jerrie Cobb standing before the press, pushing for “women in space” was definitely, irrefutably a distraction he didn’t need. And any resources devoted to it were being pulled directly away from the moon shot—which, to Johnson, was the goal.

Jerrie Cobb poses next to a Mercury spaceship capsule
Jerrie Cobb poses next to a Mercury spaceship capsule
NASA, Public Domain, Wikimedia Commons

Cobb has always maintained the women were misled and betrayed. I’ve found no evidence of that. Testimony of many of the other participants suggests that Cobb simply got carried away—not that anyone could blame her. Let’s remember that at that time, she couldn’t have known what was really involved in space flight or what the program would look like over the next decade. No one did.

Of course, American women did start flying in space with the Space Shuttle. Do not for a moment think this means they didn’t face the same prejudices at NASA that they did everywhere else. The first class of women astronauts was, according to my sources, invited to help design an in-flight cosmetics kit—an offer they immediately and forcefully shot down. Thirty years later, women remain a distinct minority in the U.S. astronaut corps ...

The bigger question is not whether Cobb was betrayed, but why, in 1961, not a single U.S. woman had been hired to work in high-performance flight test—considering that so many (like Cobb, for example) had performed test flight and ferry duties during the war.

Why weren’t women welcome in the post-war aerospace economy, and why—even today—are so few women granted degrees in engineering of any sort? I don’t know the answer, though sexism is unquestionably in the mix, but it’s a question we need to address as a nation.

This post originally appeared on Quora. Click here to view.