In 1492, one of the first recorded meteorites fell outside a Roman village and was promptly chained inside a church as an omen of war. More than 1,000 years earlier, ancient Egyptians made funeral tools from meteorites that they believed were connected to the afterlife. Even today, humans clasp their hands, close their eyes, and whisper wishes to falling stars.
Space rocks have always inspired myth and mystery. Though science has mostly replaced the myths surrounding asteroids, shooting stars and meteor showers, people remain fascinated by these celestial phenomena. So, what are we really looking at when space rocks fly overhead, and is the science behind them just as compelling as the myths?
What is the Difference Between Asteroids and Comets?
Christian Klimczak, an associate professor at the University of Georgia, studies planetary structural geology. He explains that asteroids and comets are similar in structure and size but differ in composition and location.
Asteroids are mostly rocky or metallic and are composed of elements and minerals commonly found on Earth, including clay, nickel and iron. They typically come from the main asteroid belt between Mars and Jupiter. This is a large donut-shaped area of the universe filled with asteroids and small planets. Asteroids can range in size from a few feet in diameter to miles wide. The asteroid Vesta is 300 miles in diameter!
“Vesta was actually on the way to becoming an Earth-like planet,” says Klimczak, “But planet formation stopped along the way there early in the history of our solar system.”
There are more than a million known asteroids in our solar system. Some, known as near-Earth objects, cross Earth’s orbit and occasionally get close enough to catch our attention.
Comets are made of dust and ice, hardened to act like a rock thanks to the coldness of space. They originate from the Oort Cloud in the outermost reaches of our solar system, an area so distant from our planet that we don’t have any spacecraft capable of fully observing what’s out there.
When a comet is knocked out of orbit by a shooting star or another comet, it leaves the Oort Cloud and moves to the inner solar system. The sun’s heat causes the comet’s icy surface to vaporize, creating the characteristic glowing “tail.”
So while comets are the distant, icy wanderers with a flair for drama, asteroids are more grounded, quietly waiting in the asteroid belt for their moment to shine.
But how do these space rocks impact us on Earth? For the most part, they don’t. But sometimes, small pieces of comets or asteroids break off and transform into meteoroids, which have their own unique journey through space.
Meteors vs Meteorites vs Meteoroids
Asteroids and comets are whole objects that orbit the sun. A meteoroid is a fragment that breaks off from either of these objects and travels through space. It can be as small as a grain of dust or as big as a school bus and travels almost anywhere in the universe.
What is the difference between meteors, meteorites and meteoroids? They’re actually just different stages in the life of a single rock.
Once a meteoroid leaves space, enters Earth’s atmosphere, and lands on our planet’s surface, we call it a meteorite. This means that meteorites are typically very small and rare. That’s a good thing since a large meteorite could leave widespread damage on Earth’s surface.
That leaves meteors, which aren’t actually space rocks at all.
A meteor, also called a shooting star, refers to the streak of light in the sky that occurs when a meteoroid enters Earth’s atmosphere and burns up because of a reaction with the air on Earth. They are the visual phenomenon of meteoroids vaporizing as they race through the sky.
In 2013, a meteor in the Chelyabinsk region of Russia was so intense that one observer said it “felt like I was blinded by headlights,” and another said, “It suddenly became as bright as if it was day.”
Seeing one meteor can be a dazzling experience. What happens when you have hundreds?
What is a Meteor Shower?
A meteor shower occurs when Earth passes through a region of space filled with particles, typically leftover dust from comets or asteroids. However, these events aren’t random. They occur at regular times each year.
“Most space objects have regular orbits around the Sun,” says Klimczak, “and as they break apart or release debris, we pass through their remnants year after year, which is why we know when meteor showers are going to occur.”
For thousands of years, humans have documented these spectacular meteor showers. The Leonids in November light up the sky with their brilliance, while others, like the Perseids in August, leave breathtaking trails. Several major meteor showers occur every year, including:
- Quadrantid (January)
- Lyrids (April)
- Eta Aquariids (May)
- Delta Auariids (July)
- Alpha Capricornids (July)
- Perseid (August)
- Orionids (October)
- Taurids (October and November)
- Leonids (November)
- Geminids (December)
- Ursids (December)
These patterns relate to the orbit of our planet and the periodic paths of comets. These can take anywhere from a few years to tens of thousands of years to complete.
Is an Asteroid Going to Hit the Earth?
It’s common for small space debris to enter Earth’s atmosphere every day. However, the real question on people’s mind lies with larger asteroids—those that could cause massive destruction or even wipe out the Earth.
“It is not a question of ‘what are the chances?’ but ‘when is it going to happen?’” says Klimczak. “And the truth is: We just don’t know.”
An impact like the one that scientists believe killed off the dinosaurs probably happens once every 100 million years, and the last one is believed to be about 65 million years ago.
Klimczak describes this pattern as “stochastic,” or random. There could be such a catastrophic event once every 100 million years, or it could happen twice in a two-year span and then not for another 200 million years.
Though we can’t know the exact date, we can look for signs, Klimczak says. Small impacts will happen more often and leave behind craters like the mile-long Barringer Crater in Arizona. The meteorite that caused this crater is estimated to be 150 ft wide (imagine three humpback whales!). However, most physicists would consider this to be a relatively small space rock. Asteroids like Vesta, Pallas and Hygiea are several times larger. Their impact would likely lead to major loss of life if not global devastation.
“If an asteroid Vesta entered our atmosphere, the Earth as we know it would be gone. It’s probably around 30 times bigger than the asteroid that killed the dinosaurs,” says Klimczak.
While we can’t predict exactly when the next big impact will happen, our understanding of space rocks continues to evolve. What’s certain is that our fascination with these celestial events isn’t going anywhere. As we gather more knowledge, we’re getting closer to understanding how they shape the past and the future of our universe.
