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By NASA
5 Min Read What Are Asteroids? (Ages 14-18)
What are asteroids?
Asteroids are rocky objects that orbit the Sun just like planets do. In fact, sometimes asteroids are called “minor planets.” These space rocks were left behind after our solar system formed about 4.6 billion years ago.
Asteroids are found in a wide range of sizes. For example, one small asteroid, 2015 TC25, has a diameter of about 6 feet – about the size of a small car – while the asteroid Vesta is nearly 330 miles in diameter, almost as wide as the U.S. state of Arizona. Some asteroids even have enough gravity to have one or two small moons of their own.
There are more than a million known asteroids. Many asteroids are given names. An organization called the International Astronomical Union is responsible for assigning names to objects like asteroids and comets.
This illustration depicts NASA’s Psyche spacecraft as it approaches the asteroid Psyche. Once it arrives in 2029, the spacecraft will orbit the metal-rich asteroid for 26 months while it conducts its science investigation.NASA/JPL-Caltech/ASU What’s the difference between asteroids, meteors, and comets?
Although all of these celestial bodies orbit the Sun, they are not the same. Unlike asteroids, which are rocky, comets are a mix of dust and ice. Meteors are small space rocks that get pulled close enough to enter Earth’s atmosphere, where they either burn up as a shooting star or land on the ground as a meteorite.
What are asteroids made of?
Different types of asteroids are composed of different mixes of materials. Most of them are made of chondrites, which are combinations of materials such as rocks and clay. These are called “C-type” asteroids. Some, called “S-type,” are made of stony materials, while “M-type” asteroids are composed of metallic elements.
NASA’s Dawn spacecraft captured this image of Vesta as it left the giant asteroid’s orbit in 2012. The framing camera was looking down at the north pole, which is in the middle of the image.NASA/JPL-Caltech/UCLA/MPS/DLR/IDA How did the asteroids form?
Asteroids formed around the same time and in the same way as the planets in our solar system. A massive, dense cloud of gas and dust collapsed into a spinning disk, and the gravity in the disk’s center pulled more and more material toward it. Over time, these pieces repeatedly collided with each other, sometimes resulting in smaller fragments and other times clumping together, resulting in much bigger objects.
Objects with a lot of mass – like planets – produced enough gravity to pull themselves into spheres, but many smaller objects didn’t. These ended up becoming comets, small moons, and, yes, asteroids. Although some asteroids have a spherical shape, most have irregular shapes – sometimes oblong, bumpy, or jagged.
The main asteroid belt lies between Mars and Jupiter, and Trojan asteroids both lead and follow Jupiter. Scientists now know that asteroids were the original “building blocks” of the inner planets. Those that remain are airless rocks that failed to adhere to one another to become larger bodies as the solar system was forming 4.6 billion years ago.Credits: NASA, ESA and J. Olmsted (STScI) Where are asteroids found?
Most of the asteroids we know about are located in an area called the main asteroid belt, which is found in the space between Mars and Jupiter. But asteroids are found in other parts of the solar system, too.
Trojan asteroids orbit the Sun on the same orbital path as a planet. They’re found at two specific points on the planetary orbit called Lagrange points. At these points, the gravitational pull of the planet and the Sun are in balance, making these points gravity-neutral and stable. Many planets have been found to have Trojan asteroids, including Earth.
An asteroid’s location can also be influenced by the gravity of planets it passes and end up pushed or pulled onto a path that brings it close to Earth. When asteroids or comets are on an orbital path that comes within 30 million miles of Earth’s orbit, we call them near-Earth objects.
Illustration of NASA’s DART spacecraft and the Italian Space Agency’s (ASI) LICIACube, with images of the asteroids Dimorphos and Didymos obtained by the DART spacecraft.Credit: NASA/Johns Hopkins APL/Joshua Diaz Could an asteroid come close enough to hit Earth?
Yes! Throughout history, asteroids or pieces of asteroids have collided with Earth, our Moon, and the other planets, too. The effects of some of these impacts are still visible. For example, Chicxulub Crater was created 65 million years ago when a massive asteroid struck Mexico’s Yucatan Peninsula. The resulting cloud of dust and gas released into Earth’s atmosphere blocked sunlight, leading to a mass extinction that included the dinosaurs. More recently, in 2013, people in Chelyabinsk, Russia, witnessed an asteroid almost as wide as a tennis court explode in the atmosphere above them. That event produced a powerful shockwave that caused injuries and damaged structures.
This is why NASA’s Planetary Defense Coordination Office keeps a watchful eye on near-Earth objects. The Planetary Defense team relies on telescopes and observatories on Earth and in space to detect and monitor objects like these that could stray too close to our planet.
The agency is working on planetary defense strategies to use if an asteroid is discovered to be heading our way. For example, NASA’s DART (Double Asteroid Redirection Test) mission in 2022 was a first-of-its-kind test: an uncrewed spacecraft with an autonomous targeting system intentionally flew into the asteroid Dimorphos, successfully changing its orbit.
Jason Dworkin, OSIRIS-REx mission project scientist, holds up a vial containing part of the sample from asteroid Bennu in 2023.Credit: NASA/James Tralie How does NASA study asteroids?
NASA detects and tracks asteroids using telescopes on the ground and in space, radar observations, and computer modeling. The agency also has launched several robotic explorers to learn more about asteroids. Some missions study asteroids from above, such as the Psyche mission, launched in 2023 to study the asteroid Psyche beginning in 2029. Other missions have actually made physical contact with asteroids. For example, the DART mission mentioned above impacted an asteroid to change its orbit, and the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification and Security – Regolith Explorer) spacecraft collected a sample of material from the surface of asteroid Bennu and delivered the sample to Earth in 2023 for scientists to study.
Career Corner
Want a career where you get to study asteroids? Here are some jobs at NASA that do just that:
Astronomer: These scientists observe and study planets, stars, and galaxies. Astronomers make discoveries that help us understand how the universe works and how it is changing. This job requires a strong educational background in science, math, and computer science. Geologist: Asteroids are made of different types of rock, clay, or metallic materials. Geologists study the properties and composition of these materials to learn about the processes that have shaped Earth and other celestial bodies, like planets, moons, and asteroids. More About Asteroids
Asteroid Facts
Gallery: What’s That Space Rock?
Center for Near Earth Object Studies
Planetary Defense at NASA
Asteroid Watch: Keeping an Eye on Near-Earth Objects
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By NASA
5 min read
How NASA Science Data Defends Earth from Asteroids
Artist’s impression of NASA’s DART mission, which collided with the asteroid Dimorphos in 2022 to test planetary defense techniques. Open science data practices help researchers identify asteroids that pose a hazard to Earth, opening the possibility for deflection should an impact threat be identified. NASA/Johns Hopkins APL/Steve Gribben The asteroid 2024 YR4 made headlines in February with the news that it had a chance of hitting Earth on Dec. 22, 2032, as determined by an analysis from NASA’s Center for Near Earth Object Studies (CNEOS) at the agency’s Jet Propulsion Laboratory in Southern California. The probability of collision peaked at over 3% on Feb. 18 — the highest ever recorded for an object of its size. This sparked concerns about the damage the asteroid might do should it hit Earth.
New data collected in the following days lowered the probability to well under 1%, and 2024 YR4 is no longer considered a potential Earth impactor. However, the event underscored the importance of surveying asteroid populations to reveal possible threats to Earth. Sharing scientific data widely allows scientists to determine the risk posed by the near-Earth asteroid population and increases the chances of identifying future asteroid impact hazards in NASA science data.
“The planetary defense community realizes the value of making data products available to everyone,” said James “Gerbs” Bauer, the principal investigator for NASA’s Planetary Data System Small Bodies Node at the University of Maryland in College Park, Maryland.
How Scientists Spot Asteroids That Could Hit Earth
Professional scientists and citizen scientists worldwide play a role in tracking asteroids. The Minor Planet Center, which is housed at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, collects and verifies vast numbers of asteroid and comet position observations submitted from around the globe. NASA’s Small Bodies Node distributes the data from the Minor Planet Center for anyone who wants to access and use it.
A near-Earth object (NEO) is an asteroid or comet whose orbit brings it within 120 million miles of the Sun, which means it can circulate through Earth’s orbital neighborhood. If a newly discovered object looks like it might be an NEO, information about the object appears on the Minor Planet Center’s NEO Confirmation Page. Members of the planetary science community, whether or not they are professional scientists, are encouraged to follow up on these objects to discover where they’re heading.
The asteroid 2024 YR4 as viewed on January 27, 2025. The image was taken by the Magdalena Ridge 2.4m telescope, one of the largest telescopes in NASA’s Planetary Defense network. Asteroid position information from observations such as this one are shared through the Minor Planet Center and NASA’s Small Bodies Node to help scientists pinpoint the chances of asteroids colliding with Earth. NASA/Magdalena Ridge 2.4m telescope/New Mexico Institute of Technology/Ryan When an asteroid’s trajectory looks concerning, CNEOS alerts NASA’s Planetary Defense Coordination Office at NASA Headquarters in Washington, which manages NASA’s ongoing effort to protect Earth from dangerous asteroids. NASA’s Planetary Defense Coordination Office also coordinates the International Asteroid Warning Network (IAWN), which is the worldwide collaboration of asteroid observers and modelers.
Orbit analysis centers such as CNEOS perform finer calculations to nail down the probability of an asteroid colliding with Earth. The open nature of the data allows the community to collaborate and compare, ensuring the most accurate determinations possible.
How NASA Discovered Risks of Asteroid 2024 YR4
The asteroid 2024 YR4 was initially discovered by the NASA-funded ATLAS (Asteroid Terrestrial-impact Last Alert System) survey, which aims to discover potentially hazardous asteroids. Scientists studied additional data about the asteroid from different observatories funded by NASA and from other telescopes across the IAWN.
At first, 2024 YR4 had a broad uncertainty in its future trajectory that passed over Earth. As the planetary defense community collected more observations, the range of possibilities for the asteroid’s future position on Dec. 22, 2032 clustered over Earth, raising the apparent chances of collision. However, with the addition of even more data points, the cluster of possibilities eventually moved off Earth.
This visualization from NASA’s Center for Near Earth Object Studies shows the evolution of the risk corridor for asteroid 2024 YR4, using data from observations made up to Feb. 23, 2025. Each yellow dot represents the asteroid’s possible location on Dec. 22, 2032. As the range of possible locations narrowed, the dots at first converged on Earth, before skewing away harmlessly. NASA/JPL/CNEOS Having multiple streams of data available for analysis helps scientists quickly learn more about NEOs. This sometimes involves using data from observatories that are mainly used for astrophysics or heliophysics surveys, rather than for tracking asteroids.
“The planetary defense community both benefits from and is beneficial to the larger planetary and astronomy related ecosystem,” said Bauer, who is also a research professor in the Department of Astronomy at the University of Maryland. “Much of the NEO survey data can also be used for searching astrophysical transients like supernova events. Likewise, astrophysical sky surveys produce data of interest to the planetary defense community.”
How Does NASA Stop Asteroids From Hitting Earth?
In 2022, NASA’s DART (Double Asteroid Redirection Test) mission successfully impacted with the asteroid Dimorphos, shortening the time it takes to orbit around its companion asteroid Didymos by 33 minutes. Didymos had no chance of hitting Earth, but the DART mission’s success means that NASA has a tested technique to consider when addressing a future asteroid potential impact threat.
Artist’s impression of NASA’s upcoming NEO Surveyor mission, which will search for potentially hazardous near-Earth objects. The mission will follow open data practices to improve the chances of identifying dangerous asteroids. NASA/JPL-Caltech To increase the chances of discovering asteroid threats to Earth well in advance, NASA is working on a new space-based observatory, NEO Surveyor, which will be the first spacecraft specifically designed to look for asteroids and comets that pose a hazard to Earth. The mission is expected to launch in the fall of 2027, and the data it collects will be available to everyone through NASA archives.
“Many of the NEOs that pose a risk to Earth remain to be found,” Bauer said. “An asteroid impact has a very low likelihood at any given time, but consequences could be high, and open science is an important component to being vigilant.”
For more information about NASA’s approach to sharing science data, visit:
https://science.nasa.gov/open-science.
By Lauren Leese
Web Content Strategist for the Office of the Chief Science Data Officer
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Last Updated Apr 10, 2025 Related Terms
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By USH
Researchers utilizing publicly available Synthetic Aperture Radar (SAR) data from Capella Space and Umbra have uncovered significant hidden structures within and beneath the CFR Pyramid on the Giza Plateau. The study reveals five distinct "Zed" structures located above what was previously believed to be the pharaoh’s burial chamber, resembling similar formations found in the Khufu Pyramid. These structures are connected by geometric pathways, with additional secondary formations identified through satellite imaging.
Source and credit images: The Reese report / The Kafre Research Project.
Most notably, eight vertically aligned cylindrical structures, arranged in two parallel rows from north to south, extend 648 meters underground. These formations merge into two massive cubic structures, each approximately 80 meters per side. Tomographical analysis indicates that the cylindrical structures function as hollow wells surrounded by descending spiral pathways.
Further research suggests that these subterranean formations are not limited to the CFR Pyramid but extend beneath the Khufu and Menkaure pyramids as well, reaching depths of approximately two kilometers. The study marks a groundbreaking advancement in the understanding of the Giza Plateau’s underground complexity,
The discoveries surrounding the CFR Pyramid represent just the tip of a vast and complex structure beneath the Giza Plateau.If confirmed, this discovery could challenge mainstream Egyptology’s belief that the pyramids were simply royal tombs.
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By NASA
4 min read
NASA Atmospheric Wave-Studying Mission Releases Data from First 3,000 Orbits
Following the 3,000th orbit of NASA’s AWE (Atmospheric Waves Experiment) aboard the International Space Station, researchers publicly released the mission’s first trove of scientific data, crucial to investigate how and why subtle changes in Earth’s atmosphere cause disturbances, as well as how these atmospheric disturbances impact technological systems on the ground and in space.
“We’ve released the first 3,000 orbits of data collected by the AWE instrument in space and transmitted back to Earth,” said Ludger Scherliess, principal investigator for the mission and physics professor at Utah State University. “This is a view of atmospheric gravity waves never captured before.”
Available online, the data release contains more than five million individual images of nighttime airglow and atmospheric gravity wave observations collected by the instrument’s four cameras, as well as derived temperature and airglow intensity swaths of the ambient air and the waves.
This image shows AWE data combined from two of the instrument’s passes over the United States. The red and orange wave-structures show increases in brightness (or radiance) in infrared light produced by airglow in Earth’s atmosphere. NASA/AWE/Ludger Scherliess “AWE is providing incredible images and data to further understand what we only first observed less than a decade ago,” said Esayas Shume, AWE program scientist at NASA Headquarters in Washington. “We are thrilled to share this influential data set with the larger scientific community and look forward to what will be discovered.”
Members of the AWE science team gather in the mission control room at Utah State University to view data collected by the mapping instrument mounted on the outside of the International Space Station. SDL/Allison Bills Atmospheric gravity waves occur naturally in Earth’s atmosphere and are formed by Earth’s weather and topography. Scientists have studied the enigmatic phenomena for years, but mainly from a few select sites on Earth’s surface.
“With data from AWE, we can now begin near-global measurements and studies of the waves and their energy and momentum on scales from tens to hundreds and even thousands of kilometers,” Scherliess said. “This opens a whole new chapter in this field of research.”
Data from AWE will also provide insight into how terrestrial and space weather interactions affect satellite communications, and navigation, and tracking.
“We’ve become very dependent on satellites for applications we use every day, including GPS navigation,” Scherliess said. “AWE is an attempt to bring science about atmospheric gravity waves into focus, and to use that information to better predict space weather that can disrupt satellite communications. We will work closely with our collaborators to better understand how these observed gravity waves impact space weather.”
AWE’s principal investigator, Ludger Scherliess, briefs collaborators of initial analysis of early AWE data. Information from the NASA-funded mission is helping scientists better understand how weather on Earth affects weather in space. SDL/Allison Bills The tuba-shaped AWE instrument, known as the Advanced Mesospheric Temperature Mapper or AMTM, consists of four identical telescopes. It is mounted to the exterior of the International Space Station, where it has a view of Earth.
As the space station orbits Earth, the AMTM’s telescopes capture 7,000-mile-long swaths of the planet’s surface, recording images of atmospheric gravity waves as they move from the lower atmosphere into space. The AMTM measures and records the brightness of light at specific wavelengths, which can be used to create air and wave temperature maps. These maps can reveal the energy of these waves and how they are moving through the atmosphere.
To analyze the data and make it publicly available, AWE researchers and students at USU developed new software to tackle challenges that had never been encountered before.
“Reflections from clouds and the ground can obscure some of the images, and we want to make sure the data provide clear, precise images of the power transported by the waves,” Scherliess said. “We also need to make sure the images coming from the four separate AWE telescopes on the mapper are aligned correctly. Further, we need to ensure stray light reflections coming off the solar panels of the space station, along with moonlight and city lights, are not masking the observations.”
As the scientists move forward with the mission, they’ll investigate how gravity wave activity changes with seasons around the globe. Scherliess looks forward to seeing how the global science community will use the AWE observations.
“Data collected through this mission provides unprecedented insight into the role of weather on the ground on space weather,” he said.
AWE is led by Utah State University in Logan, Utah, and it is managed by the Explorers Program Office at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Utah State University’s Space Dynamics Laboratory built the AWE instrument and provides the mission operations center.
By Mary-Ann Muffoletto
Utah State University, Logan, UT
NASA Media Contact: Sarah Frazier
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Last Updated Mar 14, 2025 Related Terms
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By NASA
5 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
Cliffs slope into the ocean in San Simeon, California. All along the state’s dynamic coastline, land is inching down and up due to natural and human-caused factors. A bet-ter understanding of this motion can help communities prepare for rising seas.NASA/JPL-Caltech The elevation changes may seem small — amounting to fractions of inches per year — but they can increase or decrease local flood risk, wave exposure, and saltwater intrusion.
Tracking and predicting sea level rise involves more than measuring the height of our oceans: Land along coastlines also inches up and down in elevation. Using California as a case study, a NASA-led team has shown how seemingly modest vertical land motion could significantly impact local sea levels in coming decades.
By 2050, sea levels in California are expected to increase between 6 and 14.5 feet (15 and 37 centimeters) higher than year 2000 levels. Melting glaciers and ice sheets, as well as warming ocean water, are primarily driving the rise. As coastal communities develop adaptation strategies, they can also benefit from a better understanding of the land’s role, the team said. The findings are being used in updated guidance for the state.
“In many parts of the world, like the reclaimed ground beneath San Francisco, the land is moving down faster than the sea itself is going up,” said lead author Marin Govorcin, a remote sensing scientist at NASA’s Jet Propulsion Laboratory in Southern California.
The new study illustrates how vertical land motion can be unpredictable in scale and speed; it results from both human-caused factors such as groundwater pumping and wastewater injection, as well as from natural ones like tectonic activity. The researchers showed how direct satellite observations can improve estimates of vertical land motion and relative sea level rise. Current models, which are based on tide gauge measurements, cannot cover every location and all the dynamic land motion at work within a given region.
Local Changes
Researchers from JPL and the National Oceanic and Atmospheric Administration (NOAA) used satellite radar to track more than a thousand miles of California coast rising and sinking in new detail. They pinpointed hot spots — including cities, beaches, and aquifers — at greater exposure to rising seas now and in coming decades.
To capture localized motion inch by inch from space, the team analyzed radar measurements made by ESA’s (the European Space Agency’s) Sentinel-1 satellites, as well as motion velocity data from ground-based receiving stations in the Global Navigation Satellite System. Researchers compared multiple observations of the same locations made between 2015 to 2023 using a processing technique called interferometric synthetic aperture radar (InSAR).
Scientists mapped land sinking (indicated in blue) in coastal California cities and in parts of the Central Valley due to factors like soil compaction, erosion, and groundwater withdrawal. They also tracked uplift hot spots (shown in red), including in Long Beach, a site of oil and gas production. NASA Earth Observatory Homing in on the San Francisco Bay Area — specifically, San Rafael, Corte Madera, Foster City, and Bay Farm Island — the team found the land subsiding at a steady rate of more than 0.4 inches (10 millimeters) per year due largely to sediment compaction. Accounting for this subsidence in the lowest-lying parts of these areas, local sea levels could rise more than 17 inches (45 centimeters) by 2050. That’s more than double the regional estimate of 7.4 inches (19 centimeters) based solely on tide gauge projections.
Not all coastal locations in California are sinking. The researchers mapped uplift hot spots of several millimeters per year in the Santa Barbara groundwater basin, which has been steadily replenishing since 2018. They also observed uplift in Long Beach, where fluid extraction and injection occur with oil and gas production.
The scientists further calculated how human-induced drivers of local land motion increase uncertainties in the sea level projections by up to 15 inches (40 centimeters) in parts of Los Angeles and San Diego counties. Reliable projections in these areas are challenging because the unpredictable nature of human activities, such as hydrocarbon production and groundwater extraction, necessitating ongoing monitoring of land motion.
Fluctuating Aquifers, Slow-Moving Landslides
In the middle of California, in the fast-sinking parts of the Central Valley (subsiding as much as 8 inches, or 20 centimeters, per year), land motion is influenced by groundwater withdrawal. Periods of drought and precipitation can alternately draw down or inflate underground aquifers. Such fluctuations were also observed over aquifers in Santa Clara in the San Francisco Bay Area, Santa Ana in Orange County, and Chula Vista in San Diego County.
Along rugged coastal terrain like the Big Sur mountains below San Francisco and Palos Verdes Peninsula in Los Angeles, the team pinpointed local zones of downward motion associated with slow-moving landslides. In Northern California they also found sinking trends at marshlands and lagoons around San Francisco and Monterey bays, and in Sonoma County’s Russian River estuary. Erosion in these areas likely played a key factor.
Scientists, decision-makers, and the public can monitor these and other changes occurring via the JPL-led OPERA (Observational Products for End-Users from Remote Sensing Analysis) project. The OPERA project details land surface elevational changes across North America, shedding light on dynamic processes including subsidence, tectonics, and landslides.
The OPERA project will leverage additional state-of-the-art InSAR data from the upcoming NISAR (NASA-Indian Space Research Organization Synthetic Aperture Radar) mission, expected to launch within the coming months.
News Media Contacts
Jane J. Lee / Andrew Wang
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-0307 / 626-379-6874
jane.j.lee@jpl.nasa.gov / andrew.wang@jpl.nasa.gov
Written by Sally Younger
2025-015
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Last Updated Feb 10, 2025 Related Terms
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