What's That Space Rock?

Asteroids are rocky, airless worlds that orbit our sun. They are remnants left over from the formation of our solar system. They can be about as wide as a car to about as wide as the state of Utah. Most of the asteroids in our solar system come from a rock-filled region called the Asteroid Belt. This vast, doughnut-shaped ring between the orbits of Mars and Jupiter contains hundreds of thousands of asteroids – maybe even millions!

Because asteroids orbit our sun, we can actually keep track of where they are and where they are headed. In fact, NASA’s Center for Near Earth Object Studies, or CNEOS, does that very thing: They use telescopes on the ground and in space to spot new asteroids and comets, keep track of where they’re going, and determine whether they might pose any risk to Earth.

About the Image: This is a still image from an animation of the giant asteroid Vesta, which resides in the asteroid belt between Mars and Jupiter. The animation was made using images taken by NASA’s Dawn spacecraft, which orbited Vesta for a little more than a year before heading to its next and final destination, the dwarf planet Ceres. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Comets also orbit the Sun, but they are more like space snowballs than space rocks. Each comet has a frozen center called a nucleus that contains icy chunks of frozen gases, bits of rock and dust. When a comet’s orbit brings it close to the Sun, it heats up and spews dust and gases, forming a giant, glowing ball around its nucleus and two tails – one made of dust and the other of gas ions. The tails trail behind the comet, away from the Sun, sometimes for millions of miles, or kilometers.

About the Image: Comet Hale Bopp, shown in this image, is one of the most well known and observed comets. Discovered in 1995, it was visible with the naked eye to viewers on Earth for 18 months between 1996 and 1997 while it was in perihelion – meaning the closest point to the Sun in its orbit. Credit: NASA

Meteoroids are fragments and debris from asteroids, comets, moons and planets. They are among the smallest “space rocks.” However, we Earthlings can actually see them when they streak through our atmosphere in the form of meteors and meteor showers.

About the Image: In 2013, NASA’s Hubble Space Telescope captured these scenes of an asteroid breaking apart. It was the first time the phenomenon had been observed. Credit: NASA, ESA, D. Jewitt (UCLA) | Read more about the image

Meteors are meteoroids (fragments of asteroids, comets, moons and planets) that fall through Earth’s atmosphere at extremely fast speeds. The pressure and heat they generate causes them to glow and create a streak of light in the sky. Some may burn up completely before touching the ground. We often refer to them as “shooting stars.” Meteors may be made mostly of rock, metal or a combination of the two.

About the Image: A meteor lights up the sky over the top of a mountain ridge near Park City, Utah. Credit: NASA/JPL-Caltech | Read more about the image

Meteor showers occur when Earth passes through trails of particles left by comets. When the particles enter Earth’s atmosphere, they burn up, creating hundreds or even thousands of bright trails in the sky that can be seen by viewers on Earth. We can easily plan when to watch meteor showers because numerous showers happen annually as Earth’s orbit takes it through the same patch of comet debris.

About the Image: Meteors stream through the sky in this photograph from the Perseid meteor shower in August. Credit: NASA/JPL-Caltech

Meteorites are asteroid, comet, moon and planet fragments (meteoroids) that survive the journey all the way to Earth’s surface. Scientists estimate that tonnes of meteoric material falls to Earth each day (mostly over the ocean) but most is extremely tiny and poses no threat to Earth.

About the Image: The dark object in the bottom right of this image is a meteorite from the small asteroid 2008 TC3, which landed in Sudan's Nubian Desert in 2008.

Dwarf planets are similar to planets. They are massive enough to be shaped by gravity into a round or nearly round shape, but they don’t have enough of their own gravitational muscle to clear their path around the Sun of other objects. In our solar system, dwarf planets are usually found in the Kuiper Belt beyond Neptune, but at least one is in the asteroid belt. If you’re wondering what happened to Pluto’s planet status, look no further than this category.

Find out more about dwarf planets in a minute! Space Shorts: What Is a Dwarf Planet?

About the Image: In this rendering made with images from NASA’s Dawn spacecraft, the dwarf planet Ceres is shown in false-color to highlight differences in the materials on its surface. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA | Read more about the image