SCIENCE

Geography is destiny for space rocks. A single space rock can go from asteroid or comet to meteoroid to meteor to meteorite, depending on where it is in the solar system at the time. (Royal Observatory Greenwich)

Sort out your space rocks here.

Teachers, scroll down for a quick list of key resources in our Teachers’ Toolkit.

Discussion Ideas

ASTEROIDS

• What are asteroids?
  • Asteroids are blobby, irregularly shaped space rocks, ranging from about 6 meters (20 feet) to about 930 kilometers (580 miles) in diameter.

 

• Where in our solar system can you find asteroids?
  • You can find most asteroids in the conveniently named Asteroid Belt, a “solar junkyard” between the orbits of Mars and Jupiter.

 

• How did asteroids get in our solar system?
  • Asteroids formed from the same rocks as our early solar system, but “due to the mighty gravitational effects of Jupiter, these chunks of rock and metal couldn’t come together to form a planet.”

 

METEOROIDS

• What are meteoroids? Take a read through our great encyclopedic entry for some help.
  • Meteoroids are smaller versions of asteroids—lumps of rock or metal that orbit the sun.

 

• Where in our solar system can you find meteoroids?
  • According to our encyclopedic entry, meteoroids, especially the tiny particles called micrometeroids, are extremely common throughout the solar system. They orbit the sun among the rocky inner planets, as well as the gas giants that make up the outer planets. Meteoroids are even found on the very edge of the solar system, in regions called the Kuiper belt and the Oort cloud.

 

• How do meteoroids form?
  • Meteoroids form in three distinct ways.
    • Most meteoroids are formed from the collision of asteroids. As asteroids smash into each other, they produce crumbly debris—meteoroids. Sometimes, the force of the collision can throw the meteoroids out orbit and put them on a collision course with a planet or moon.
    • Others meteoroids are the debris that comets shed as they travel through space. As a comet approaches the sun, the comet’s nucleus, nicknamed a “dirty snowball” or “snowy dirtball”, sheds gas and dust. This debris is visible as the comet’s tail. The dusty tail may contain hundreds or even thousands of meteoroids and micrometeroids. Meteoroids shed by a comet usually orbit together in a formation called a meteoroid stream.
    • Finally, a very small percentage of meteoroids are rocky pieces that break off from the Moon and Mars after big celestial bodies—often asteroids—impact their surfaces. Most impacts leave a crater and a scattering of debris, but meteoroid-producing impacts are so powerful that some of that debris is thrown right out of the gravitational pull of the planet or moon.

 

METEORS

• What are meteors? Take a read through our great encyclopedic entry for some help.
  • Meteors are space rocks (meteoroids) burning up as they crash through Earth’s atmosphere. Meteors are nicknamed “shooting stars” or “falling stars.”

 

• Where can you find meteors?
  • In the atmosphere: Most meteors occur in Earth’s mesosphere, about 50-80 kilometers (31-50 miles) above the Earth’s surface.
  • In the sky: As the Earth passes through a comet’s tail, the rocky debris collides with our atmosphere, creating the colorful streaks of a meteor shower. Meteor storms are even more intense than showers, defined as having at least 1,000 meteors per hour.
    • All the meteors in a meteor shower seem to come from one spot in the sky. This spot is called the radiant point, or simply the radiant.
    • Meteor showers are named after the constellation in which their radiant appears. The source of the meteors is not the constellation, of course, but rather the comet from which they have broken off. For example, the Leonid meteor shower appears to produce meteors falling from the constellation Leo, but the meteors are actually debris from Comet Tempel-Tuttle.

 

• Why are meteors burning up?
  • The meteor’s velocity, and how that velocity impacts friction and temperature.
    • Friction: When a space rock enters the Earth’s upper atmosphere, it increases friction among the surrounding air particles. This friction causes gases around the rock to ignite and glow brightly.
    • Temperature: The velocity of the space rock compresses the gases right in front of it. Compressing a gas increases its temperature.

 

• Why do some meteors appear for a few seconds, while others are visible for more than a minute?
  • It has to do with the size and velocity of the space rock. The smallest meteors glow for about a second, while larger and faster meteors can be visible for several minutes.

 

METEORITES

• What are meteorites? Take a read through our great encyclopedic entry for some help.
  • Meteorites are space rocks (meteors) that actually impact Earth’s surface.

 

• Where on Earth can you find meteorites?
  • Meteorites can fall to Earth anywhere, although they’re most commonly found in isolated places such as Antarctica, the Sahara Desert, and Siberia.
    • Click here to learn about a 654-kilogram meteorite recovered from the bottom of a Russian lake in 2013.
    • Click here for a fun map that shows where Martian meteorites—rocks from Mars—have been found on Earth.

 

ROCKY REGIONS OF SPACE

• Where is our solar system’s “snow line”?
  • The snow line starts just beyond Jupiter’s orbit, where objects contain a lot of ice.

 

• Where is the Kuiper belt?
  • The Kuiper belt is a group of icy space rocks that lie about 40 AU away from the sun, just beyond the orbit of Neptune, the outermost (verified!) planet in our solar system.

 

• Where is the Oort cloud?
  • The Oort cloud is a group of millions of icy space rocks that orbit at the very edge of our solar system, up to 100,000 AU (!) away from the sun.

 

COMETS

• What are comets?
  • Comets are space rocks made up of ice, gas, and dust.

 

• Where in our solar system can you find comets?
  • Just like everything else in the neighborhood, comets orbit the sun. (It’s called the solar system for a reason!) Most comets have their origin in the icy outskirts of the Kuiper belt and Oort cloud, though.

 

• Why does a comet have a tail?
  • According to the good folks at Hubble, “As a comet approaches the sun, it starts to heat up. The ice transforms directly from a solid to a vapor, releasing the dust particles embedded inside. Sunlight and the stream of charged particles flowing from the sun—the solar wind—sweeps the material back in a long tail [pointing away from the sun]. The comet’s ingredients determine the types and number of tails.” There are two types of comet tails: dust tails and gas ion tails.
    • Dust tails contain small, solid particles that are about the same size found in cigarette smoke. Dust tails form because sunlight pushes on these small particles, gently shoving them away from the comet’s nucleus. Because the pressure from sunlight is relatively weak, the dust particles end up forming a diffuse, curved tail.
    • Gas ion tails are not space rocks. Gas ion tails form when ultraviolet sunlight rips one or more electrons from gas atoms in the comet, making them into ions. The solar wind then carries these ions straight outward away from the Sun. The resulting tail is straighter and narrower [than a dust tail].

 

ET CETERA

• What are near-earth objects? Take a look at this NASA poster for some help.
  • Near-Earth objects are defined as any big space rocks (usually asteroids or comets) whose orbit brings them within 1.3 AU (about 121 million miles) of Earth. Some of these might pose a threat—particularly a group called PHAs, or potentially hazardous asteroids. But don’t worry, NASA’s on the job. Learn more about the Near Earth Object Program here.

 

• Are there any space rocks the great Royal Observatory video left out?
  • Just the big ones—planets and dwarf planets.

 

TEACHERS’ TOOLKIT

Royal Observatory Greenwich: Space Rocks!

Nat Geo: What’s That Space Rock?

Nat Geo: What is a meteoroid?

Nat Geo: What is a meteor?

Nat Geo: What is a meteorite?

Nat Geo: Martian Meteorites map

NASA: Near Earth Object Program FAQ