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AsteroidsAsteroids are small, rocky bodies left over from the early formation of the solar system. More than 1 million asteroids orbit the sun—primarily in the asteroid belt between Mars and Jupiter—ranging in size from bus-length to hundreds of miles in diameter. Astronomers catalog and study these objects to identify threats to Earth and better understand the solar system's history.
The search for asteroids began somewhat accidentally at the turn of the 19th century, when a group of scientists calling themselves the "Celestial Police" began searching for a suspected missing planet between the orbits of Mars and Jupiter. After Giuseppe Piazzi independently discovered Ceres, various members discovered three smaller celestial bodies: Pallas, Juno, and Vesta. All four were initially described as planets, but subsequent discoveries of smaller bodies prompted a new classification term: asteroids.
NASA's NEO Observations Program has detected over 40,000 near-Earth asteroids—those orbiting within 30 million miles of Earth. NASA has identified 95% of near-Earth asteroids over 0.6 miles in length, which are capable of causing global extinction events, though it continues to work toward identifying at least 90% of smaller, city-killing asteroids.Explore Asteroids
What we've found
Asteroids are the rocky remains of the solar system's formationThese celestial bodies were not integrated into the precursors of planets about 4.6 billion years ago and instead continue to orbit the sun, primarily within a band between Mars and Jupiter—the asteroid belt. Science ABCDark comets appear to be rocky asteroids but move like cometsCometary orbits are known to exhibit accelerations independent of gravity that result from forces related to the release of gases. Dark comets exhibit this behavior but lack visible clouds of frozen material that have turned into a gas—the coma the comets display—indicating minor quantities of escaping subsurface ice. University of MichiganShooting stars, or meteors, are fragments of asteroids and cometsThese objects range in size from a grain of sand to a pebble and originate from the breaking apart of rocky asteroids due to collisions or from the debris of icy comets' tails. As they enter Earth's atmosphere, they burn up, creating streaks in the sky called meteor showers. NASAEarth's water may have come from comets, asteroids, or its magma oceanBefore Earth's atmosphere formed, any liquid water would have boiled off, preventing the accumulation of water early on to create today's oceans. Planetary scientists continue to debate whether this water was delivered later from comet or asteroid collisions or via reactions between iron oxide in Earth's molten surface and hydrogen gas from the planetary nebula. Short WaveMar's moons, Phobos and Deimos, are thought to be captured asteroidsOf the two Martian moons, Phobos orbits more quickly, completing three revolutions a day. It gets 1.8 meters closer to Mars every year, and may crash into the planet in about 50 million years. NASA ScienceAbout 20% of asteroids are metal worlds similar to Earth's coreThe biggest of these (that we know of) is 16 Psyche. Measuring 140 miles across, its iron and nickel content is potentially worth 10,000 quadrillion dollars. NASA’s mission to Psyche—reaching the asteroid in 2029—will study it to learn about its formation. CelestiumThe 'Celestial Police' accidentally discovered asteroids while planet huntingThe group was formed in 1800 to find a planet some astronomers believed existed between Mars and Jupiter. Prior to their disbanding in 1815, the group instead discovered Vesta, Juno, and other objects they would call asteroids. BBC Sky at Night MagazineNASA's Near-Earth Object Surveyor can detect asteroids coming from the sunTelescopes directed at the sun or lacking heat shields may become damaged, limiting our ability to monitor potentially dangerous objects coming from that direction. The NEO Surveyor is built to overcome this problem and spot asteroids that reflect as little as 5% of incoming light. New ScientistNASA monitors potentially hazardous asteroids and cometsEstablished in 2016, the Planetary Defense Coordination Office characterizes and tracks asteroids and comets passing within 30 million miles of Earth. Over 40,000 near-Earth asteroids have been discovered, although estimates suggest that about 14,000 more such objects remain to be found. NASA ScienceAsteroids are artifacts of water's presence in the solar systemAsteroids contributed to planet formation and carried water from the solar system's outer reaches toward the center. They were also early providers of the necessary elements and conditions for life to evolve on Earth. AxiosAsteroids were discovered by 18th-century planet huntersWhile looking for a planet between Mars and Jupiter to coincide with an apparent mathematical pattern in the distances of known planets from the sun, a group calling themselves the "Celestial Police" discovered multiple objects that fell into a new classification. European Space AgencySimulations show unidentified asteroids around Venus may pose a threat to EarthA new study suggests that Venus' co-orbital asteroids—space rocks that lag ahead or behind the planet—could potentially destroy cities if they strike Earth. While no observed co-orbitals currently pose a threat, observational bias prevents observation of those of greater risk. Live ScienceAsteroids are often unobserved until they are days away from EarthEven those large enough to cause local or regional damage are too small, dim, and far away to be observed readily from cosmological distances. New tools, like NASA's NEO Surveyor telescope, aim to address gaps in detection systems. ReutersLaunch asteroids at EarthDesign your own asteroid and launch it at Earth! Explore the major asteroids in our solar systemThis 3D solar system visualization displays the positions of known asteroids, comets, and spacecraft involved in asteroid studies. Major asteroids include additional details, including orbital trajectories and discovery dates. NASADefending Earth against asteroidsThis three-minute video overview explains NASA's ambitious test to slightly alter the course of an asteroid by slamming a fast-moving space probe into its surface. Scientists hope to one day, if needed, use the technique to protect Earth from an asteroid impact. Johns Hopkins UniversityOnly 40% of city-destroying asteroids have been detectedStatistical modeling shows that while we have identified the majority of extinction-level asteroids, smaller asteroids that can cause significant damage remain elusive. Some asteroids, like the one that exploded over Chelyabinsk in 2013, can't be detected ahead of time since they come from the sun's direction. Kite & Key MediaMold growth in space raises the hypothesis of life being brought to EarthPanspermia suggests that life could be carried throughout the cosmos by asteroids, comets, and other objects, but it requires organisms that can withstand the extreme cold of space travel, stellar radiation, lack of water, and intense heat of planetary impacts. The discovery of mold on the International Space Station and experiments showing it can withstand radiation in outer space-like conditions increase the plausibility of the hypothesis. StarTalkExperiments suggest nuking a metal-rich asteroid may strengthen itScientists exposed meteorite samples to proton irradiation at CERN to mimic the effects of a nuclear detonation. The material exhibited greater resistance to breaking after the exposure, suggesting nuclear weapons may better serve to deflect asteroids, not break them. IFLScienceThe names of comets can change based on subsequent observationsThe International Astronomical Union's coded naming system uses the first letter to indicate a comet's category, which can change over time. "D" represents comets that have been lost or broken up, while "A" applies to former comets that are now asteroids or dwarf planets. ESAIn 2013, an asteroid was named after WikipediaA main-belt asteroid previously labeled 274301 was renamed "Wikipedia" by the Committee for Small Body Nomenclature. First observed in 2008 by astronomers at the Andrushivka Astronomical Observatory, the asteroid was renamed based on a suggestion from a member of the Wikimedia Foundation in Ukraine. NBC NewsDiscovering how the dinosaurs went extinct may have helped avert nuclear warThis NPR Throughline episode explains how the 1980 discovery that an asteroid-driven dust cloud killed the dinosaurs inspired Cold War scientists’ fears of “nuclear winter”—a sunlight-blocking aftermath of nuclear war that may have discouraged leaders from launching one. Throughline NPROne man in Arizona works to defend Earth from catastrophic space rocksDavid Rankin, an observer and operations engineer at the NASA-funded Catalina Sky Survey, spends his days scanning for solar system objects that could collide with our planet. The job requires employees to work long shifts to help prevent asteroids from destroying our planet. Smithsonian MagazineA scientist debunks theories for why aliens might invade EarthWhile TV and films offer common tropes for why aliens would invade Earth, many of those reasons aren't actually feasible. For example, a species with technology advanced enough to allow it to travel between planets likely doesn't need to enslave flawed humans to carry out its labor. Literary HubSpace trash could be cleaned up using a giant inflatable bag California-based TransAstra has developed and tested a device called Capture Bag, intended to catch anything from small rocks to house-sized boulders. The company claims its system could also be adapted for asteroid capture and mining. CNNSimulate asteroid impact, mitigation, and defense scenariosTens of thousands of asteroids are in orbit in our solar system, and only a fraction come close enough to concern humanity. This simulator allows you to see the big picture scenarios of an asteroid impact, strategies to mitigate its destruction, and how Earth could defend itself. Asteroid StrikeVariations in beak shape helped birds survive the dinosaur extinction eventThe asteroid that struck Earth 66 million years ago killed some avian dinosaurs. The smaller species endured by reproducing more quickly and adapting to the environment. Their different beaks allowed them to eat more varied foods for survival. Natural History MuseumThe resulting climate change, not the asteroid impact itself, killed most dinosaursAlthough the Chicxulub impact caused widespread destruction through earthquakes and tsunamis, the subsequent nuclear winter, acid rain, and eventual greenhouse warming drove mass extinction. Roughly 70% of species, including all non-avian dinosaurs, went extinct. National Science FoundationResearch suggests a 95-kilometer-wide (59-mile-wide) asteroid impact could boil the Earth's oceansEven a 1-kilometer-wide (0.62-mile-wide) asteroid can trigger earthquakes and tsunamis on impact with oceans. The overwhelming majority of asteroids that reach Earth are much smaller and burn up in the atmosphere before reaching the ground. SciShowExplore an interactive visualization of the solar systemThis tool allows you to view the orbits of planets, dwarf planets, moons, asteroids, and other significant objects in the solar system. Clicking on an object reveals key facts and historical data. Gordon HartCeres—the largest object in the asteroid belt—may have once harbored a muddy oceanNASA's Dawn mission revealed Ceres' surface composition, which contains salts, water ice, and organic material. Ceres' ocean likely froze over entirely in the past, when the presence of water may have allowed life to exist. Big ThinkFly through the Valles Marineris, the largest canyon in the solar systemStretching farther than the width of the continental US and with depths as much as four times those of the Grand Canyon, the Valles Marineris is believed to have formed when Mars’s crust tore open during intense volcanism in the planet’s past. VideoFromSpaceCategorization of celestial objects has changed over historyOnce classified as planets, Ceres and Vesta are now considered a dwarf planet and an asteroid, respectively. The discovery of many similarly sized objects led to the creation of the asteroid belt category. NASA Jet Propulsion Laboratory (JPL)A modern-day version of the dinosaur-killing asteroid would kill billions of peopleSuch an asteroid would level Central America, trigger tsunamis, spark global fires, and plunge the planet into an artificial winter lasting over a decade. Bunkers would be insufficient for survival without years of provisions. melodysheepWatch visualization of different-sized asteroid impactsThe animations range from a 4-meter-wide asteroid that would burn up in the atmosphere with the impact of 0.6 Hiroshima nuclear bombs to a 940-kilometer asteroid the size of the dwarf planet Ceres, which would produce a mass extinction event. MetaBallStudiosCritical organic molecules have been found on an asteroidNASA's OSIRIS-REx mission returned samples containing amino acids and nucleobases from asteroid Bennu. Without Bennu having been destroyed—as is common for asteroids that enter Earth's atmosphere—its samples serve as a time capsule of the solar system's early chemistry. NASANASA's DART mission successfully deflected an asteroidThe Double Asteroid Redirection Test crashed into asteroid moonlet Dimorphos in 2022, altering its orbital radius. The project required precise astrodynamics to strike the moonlet from 11 million kilometers away while traveling 22,530 kilometers per hour. The Wall Street JournalCongressional funding for asteroid detection has long seen bipartisan supportAlthough asteroid detection is mandated by law, the NEO Surveyor telescope, which is specifically designed to detect asteroids, received more than twice the funding requested by NASA in 2023. Undark MagazineIn 2022, NASA's OSIRIS-REx spacecraft touched down on an asteroidDust of asteroid Bennu, slightly wider than the Empire State Building is tall, was found to be rich in carbon, nitrogen, and organic compounds essential for life. The presence of magnesium-sodium phosphate indicated Bennu may have broken off from a primitive ocean world. NASA ScienceJupiter may have affected the trajectory of the asteroid that wiped out the dinosaursDespite its reputation as Earth’s cosmic shield, Jupiter’s gravity pulls more asteroids into Earth-crossing orbits. Simulations show that Earth experiences over three times more asteroid impacts because of Jupiter’s influence than if Jupiter didn’t exist. Big ThinkThe thousands of objects orbiting Jupiter include 95 officially recognized moonsJupiter's moons were first discovered on Jan. 7, 1610. They include Ganymede, the largest moon in the solar system and larger than Mercury, Io, the most volcanically active moon, and Europa, which has a saltwater ocean. NASAJupiter’s formation included accretion and migrations across the solar systemOne theory of Jupiter’s formation involves the planet spiraling inwards from the asteroid belt, gathering material and disrupting the initial formation of terrestrial planets. Saturn’s gravitational pull would then reverse its course. BBC Earth ScienceInside the most dangerous asteroid hunt everAstronomers identified asteroid 2024 YR4 in early 2025, initially giving it a 3.1% chance of hitting Earth in 2032—the highest ever probability for a large asteroid. This sparked global planetary defense plans, but further observations soon ruled out any significant impact risk, bringing relief worldwide. Here's the story of how it unfolded. MIT Technology ReviewStudies show the asteroid that killed the dinosaurs was from the outer asteroid beltIsotopic evidence confirms the rock was a carbon-rich asteroid, likely born beyond Jupiter and later knocked into Earth's path after billions of years of orbital drift and gravitational nudges. Its path spanned over 4 billion years and ended in the extinction of 75% of life, including all nonavian dinosaurs. NautilusEarth is constantly bombarded by material from spaceMost of this matter is composed of small particles, with any smaller than 33 feet in diameter burning up in the atmosphere. Larger asteroids can reach the ground, and those larger than several thousand feet cause global damage, including earthquakes and tsunamis. 1440What would happen if a massive asteroid struck Earth?While NASA states that no known asteroid currently threatens Earth, past impacts demonstrate that the risk is real. The agency has tested deflection technology to alter an asteroid's path, as this visualization imagines a worst-case collision scenario. What IfThe next five asteroid approachesAsteroids are zinging by our planet regularly, and some of them you can see without a telescope. Here's a regularly updated list of the next five asteroid approaches. NASA - National Aeronautics and Space AdministrationDinosaurs would likely still roam Earth if the Chicxulub asteroid had hit elsewhereSome scientists argue that the asteroid's impact would have been less severe if it had struck the ocean instead of shallow seas. In this scenario, small dinosaurs might have become urban survivors, living in cities alongside humans, much like pigeons or rats do today. BBCMammals gradually expanded in size and diversity after the dinosaur extinctionAfter an asteroid impact caused a mass extinction event 66 million years ago, small mammals were among the few surviving species. With fewer predators, mammals steadily grew larger as new habitats emerged. Smithsonian MagazineDino-killing asteroid struck in springClues from fossil fish help scientists pinpoint the season when Earth’s fifth mass extinction began Smithsonian Magazine