Asteroid facts for kids

Images of visited asteroids illustrating their differences: (top row) 433 Eros and 243 Ida with its moon Dactyl, (bottom row) Ceres and 101955 Bennu. Sizes are not to scale.

Asteroids are rocky, metallic, or icy space bodies with no atmosphere. Imagine a giant cosmic construction site where planets were being built! Lots of rocks and dust were flying around, and some of them never quite made it into a planet. These leftover bits are what we call asteroids. They're like space rocks, ranging in size from tiny pebbles to enormous mountains floating in space. They orbit the Sun in elliptical paths and can have irregular shapes, often resembling a "rubble pile" rather than a solid body.

Asteroids are believed to contain clues about the early solar system and the processes that led to planet formation. Studying them can provide insights into the history of our solar system.

Where do we find these space rocks?

Most asteroids live in a region between Mars and Jupiter called the asteroid belt. It's not a solid belt like a belt you wear, but more like a crowded highway in space, with millions of asteroids of all shapes and sizes zooming around. Scientists estimate there are over a million asteroids in the asteroid belt that are larger than one kilometer (about 0.6 miles) across!

But the asteroid belt isn't the only place to find these space wanderers. Some asteroids have escaped the asteroid belt and travel in different orbits around the Sun. These are called near-Earth asteroids (NEAs). Some even cross Earth's orbit! Don't worry though, most are tiny and burn up harmlessly in our atmosphere, creating beautiful shooting stars.

What are asteroids made of?

Asteroids aren't all the same. They're made of different materials, depending on where they formed in the early solar system.

Scientists classify asteroids into different types based on their composition and the light they reflect. Some common types include:

• C-type asteroids: These are the most common type, making up about 75% of all known asteroids. They're dark and made mostly of clay and silicate rocks.

• S-type asteroids: These are the second most common type, making up about 17% of known asteroids. They're brighter than C-type asteroids and are made of silicate materials and some metals.

• M-type asteroids: These are less common and are made mostly of metal, like iron and nickel.

How big are asteroids?

The size of asteroids varies enormously. Some are just a few meters across, while others are hundreds of kilometers in diameter. The largest asteroid in the asteroid belt is Ceres, which is about 946 kilometers (588 miles) in diameter. It's so big that it's actually classified as a dwarf planet!

How do we study asteroids?

Scientists use telescopes on Earth and in space to study asteroids. They observe their light to learn about their composition and orbit. Sometimes, they even send spacecraft to visit asteroids up close! These spacecraft can take pictures, collect samples, and even land on the surface of an asteroid.

One famous example is the NEAR Shoemaker spacecraft, which orbited and landed on the asteroid Eros in 2001. It sent back amazing pictures and data that helped scientists learn more about the asteroid's composition and history. Another example is the OSIRIS-REx mission, which collected a sample from the asteroid Bennu and is bringing it back to Earth for scientists to study.

Are asteroids dangerous?

While most asteroids pose no threat to Earth, some near-Earth asteroids have orbits that could potentially bring them close to our planet. Scientists are constantly monitoring these asteroids to assess the risk of a collision. If an asteroid is found to be on a collision course with Earth, there are plans to deflect it, preventing a potential impact. These plans involve using spacecraft to gently nudge the asteroid off course, ensuring the safety of our planet.

History of asteroid discoveries

Cumulative discoveries of just the near-Earth asteroids known by size, 1980–2024

The first asteroid, Ceres, was discovered on January 1, 1801, by Giuseppe Piazzi, an Italian astronomer. This discovery marked the beginning of a long and exciting journey of exploration and discovery. Since then, thousands of asteroids have been discovered, and new ones are being found all the time. The number of known asteroids is constantly growing, thanks to advanced telescopes and sophisticated detection techniques.

The first close-up observation of an asteroid was made by the Galileo spacecraft. Several dedicated missions to asteroids were subsequently launched by NASA and JAXA.

Currently all newly discovered asteroids receive a provisional designation (such as 2002 AT₄) consisting of the year of discovery and an alphanumeric code indicating the half-month of discovery and the sequence within that half-month. Once an asteroid's orbit has been confirmed, it is given a number, and later may also be given a name (e.g. 433 Eros).

Largest asteriods

Three largest objects in the asteroid belt, Ceres, Vesta, and Pallas, are intact protoplanets that share many characteristics common to planets, and are atypical compared to the majority of irregularly shaped asteroids. The fourth-largest asteroid, Hygiea, appears nearly spherical although it may have an undifferentiated interior, like the majority of asteroids. The four largest asteroids constitute half the mass of the asteroid belt.

Asteroid mining

Artist's concept of a crewed mission to an asteroid

The concept of asteroid mining was proposed in 1970s. Matt Anderson defines successful asteroid mining as "the development of a mining program that is both financially self-sustaining and profitable to its investors". It has been suggested that asteroids might be used as a source of materials that may be rare or exhausted on Earth, or materials for constructing space habitats. Materials that are heavy and expensive to launch from Earth may someday be mined from asteroids and used for space manufacturing and construction.

As resource depletion on Earth becomes more real, the idea of extracting valuable elements from asteroids and returning these to Earth for profit, or using space-based resources to build solar-power satellites and space habitats, becomes more attractive. Hypothetically, water processed from ice could refuel orbiting propellant depots.

From the astrobiological perspective, asteroid prospecting could provide scientific data for the search for extraterrestrial intelligence (SETI). Some astrophysicists have suggested that if advanced extraterrestrial civilizations employed asteroid mining long ago, the hallmarks of these activities might be detectable.

Potential threats to Earth

Near-Earth asteroids can threaten all life on the planet, as in the impact which may have inflicted the Cretaceous–Paleogene extinction. As an experiment to meet this danger, in September 2022 the Double Asteroid Redirection Test spacecraft successfully altered the orbit of the non-threatening asteroid Dimorphos by crashing into it.

Fiction

Asteroids and the asteroid belt are a staple of science fiction stories. Asteroids play several potential roles in science fiction: as places human beings might colonize, resources for extracting minerals, hazards encountered by spacecraft traveling between two other points, and as a threat to life on Earth or other inhabited planets, dwarf planets, and natural satellites by potential impact.

Interesting facts about asteriods

• Of the roughly one million known asteroids, the greatest number are located between the orbits of Mars and Jupiter, in a region known as the main asteroid belt.
• The total mass of all the asteroids combined is only 3% that of Earth's Moon.
• The majority of main belt asteroids follow slightly elliptical, stable orbits, revolving in the same direction as the Earth and taking from three to six years to complete a full circuit of the Sun.
• As of April 2022^[update], the Minor Planet Center had data on 1,199,224 asteroids in the inner and outer Solar System, of which about 614,690 had enough information to be given numbered designations.
• Asteroids become darker and redder with age due to space weathering.

Images for kids

• 

  2013 EC, shown here in radar images, has a provisional designation

• 

  Artist's impression shows how an asteroid is torn apart by the strong gravity of a white dwarf.

• 

  A top view of asteroid group location in the inner solar system.

• 

  A map of planets and asteroid groups of the inner solar system. Distances from sun are to scale, object sizes are not.

• 

  Cratered terrain on 4 Vesta

• 

  Mineral map of Vesta, showing its spectra

• 

  A complex horseshoe orbit (the vertical looping is due to inclination of the smaller body's orbit to that of the Earth, and would be absent if both orbited in the same plane)      Sun ·       Earth ·       (419624) 2010 SO16

• 

  The 70m antenna at Goldstone Observatory

• 

  Radar observations of near-Earth asteroid (505657) 2014 SR₃₃₉ as seen by Arecibo

• 

  WISE infrared space telescope

• 

  Asteroid 6481 Tenzing, center, is seen moving against a background of stars in this series of images taken by the James Webb Space Telescope's instrument NIRCam

• 

  Asteroids and comets visited by spacecraft as of 2019 (except Ceres and Vesta), to scale

• 

  Artist's concept of a crewed mission to an asteroid

• 

  Frequency of bolides, small asteroids roughly 1 to 20 meters in diameter impacting Earth's atmosphere

• 

  Artist's impression of an asteroid impact on Earth

• 

  Artist's concept of spacious structure of near-Earth asteroid 2011 MD

• 

  Hayabusa2

• 

  Dawn

• 

  Lucy

• 

  Psyche

See also

In Spanish: Asteroide para niños

• Exoasteroid
• List of minor planets
• List of exceptional asteroids
• List of asteroid close approaches to Earth
• Lost minor planet
• Meanings of minor-planet names