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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
3 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
The Jet Propulsion Laboratory perfected aerogel for the Stardust mission. Under Stardust, bricks of aerogel covered panels on a spacecraft that flew behind a comet, with the microporous material “soft catching” any particles that might strike it and preserving them for return to Earth.NASA Consisting of 99% air, aerogel is the world’s lightest solid. This unique material has found purpose in several forms — from NASA missions to high fashion.
Driven by the desire to create a 3D cloud, Greek artist, Ioannis Michaloudis, learned to use aerogel as an artistic medium. His journey spanning more than 25 years took him to the Massachusetts Institute of Technology (MIT) in Cambridge; Shivaji University in Maharashtra, India, and NASA’s Jet Propulsion Laboratory in Southern California.
A researcher at MIT introduced Michaloudis to aerogel after hearing of his cloud-making ambition, and he was immediately intrigued. Aerogel is made by combining a polymer with a solvent to create a gel and flash-drying it under pressure, leaving a solid filled with microscopic pores.
Scientists at JPL chose aerogel in the mid-1990s to enable the Stardust mission, with the idea that a porous surface could capture particles while flying on a probe behind a comet. Aerogel worked in lab tests, but it was difficult to manufacture consistently and needed to be made space-worthy. NASA JPL hired materials scientist Steve Jones to develop a flight-ready aerogel, and he eventually got funding for an aerogel lab.
The aerogel AirSwipe bag Michaloudis created for Coperni’s 2024 fall collection debut appears almost luminous in its model’s hand. The bag immediately captured the world’s attention.Coperni
The Stardust mission succeeded, and when Michaloudis heard of it, he reached out to JPL, where Jones invited him to the lab. Now retired, Jones recalled, “I went through the primer on aerogel with him, the different kinds you could make and their different properties.” The size of Jones’ reactor, enabling it to make large objects, impressed Michaloudis. With tips on how to safely operate a large reactor, he outfitted his own lab with one.
In India, Michaloudis learned recipes for aerogels that can be molded into large objects and don’t crack or shrink during drying. His continued work with aerogels has created an extensive art portfolio.
Michaloudis has had more than a dozen solo exhibitions. All his artwork involves aerogel, drawing attention with its unusual qualities. An ethereal, translucent blue, it casts an orange shadow and can withstand molten metals.
In 2020, Michaloudis created a quartz-encapsulated aerogel pendant for the centerpiece of that year’s collection from French jewelry house Boucheron. Michaloudis also captured the fashion and design world’s attention with a handbag made of aerogel, unveiled at Coperni’s 2024 fall collection debut.
NASA was a crucial step along the way. “I am what I am, and we made what we made thanks to the Stardust project,” said Michaloudis.
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Last Updated Jun 09, 2025 Related Terms
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Stardust
NASA’s Stardust was the first spacecraft to bring samples from a comet to Earth, and the first NASA mission to…
Solar System
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By NASA
NASA’s James Webb Space Telescope recently imaged the Sombrero Galaxy with its NIRCam (Near-Infrared Camera), which shows dust from the galaxy’s outer ring blocking stellar light from stars within the galaxy. In the central region of the galaxy, the roughly 2,000 globular clusters, or collections of hundreds of thousands of old stars held together by gravity, glow in the near-infrared. The Sombrero Galaxy is around 30 million light-years from Earth in the constellation Virgo. From Earth, we see this galaxy nearly “edge-on,” or from the side.NASA, ESA, CSA, STScI After capturing an image of the iconic Sombrero galaxy at mid-infrared wavelengths in late 2024, NASA’s James Webb Space Telescope has now followed up with an observation in the near-infrared. In the newest image, released on June 3, 2025, the Sombrero galaxy’s tightly packed group of stars at the galaxy’s center is illuminated while the dust in the outer edges of the disk blocks some stellar light. Studying galaxies like the Sombrero at different wavelengths, including the near-infrared and mid-infrared with Webb, as well as the visible with NASA’s Hubble Space Telescope, helps astronomers understand how this complex system of stars, dust, and gas formed and evolved, along with the interplay of that material.
Learn more about the Sombrero galaxy and what this new view can tell us.
Image credit: NASA, ESA, CSA, STScI
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By NASA
After a decade of searching, NASA’s MAVEN (Mars Atmosphere Volatile Evolution) mission has, for the first time, reported a direct observation of an elusive atmospheric escape process called sputtering that could help answer longstanding questions about the history of water loss on Mars.
Scientists have known for a long time, through an abundance of evidence, that water was present on Mars’ surface billions of years ago, but are still asking the crucial question, “Where did the water go and why?”
Early on in Mars’ history, the atmosphere of the Red Planet lost its magnetic field, and its atmosphere became directly exposed to the solar wind and solar storms. As the atmosphere began to erode, liquid water was no longer stable on the surface, so much of it escaped to space. But how did this once thick atmosphere get stripped away? Sputtering could explain it.
Sputtering is an atmospheric escape process in which atoms are knocked out of the atmosphere by energetic charge particles.
“It’s like doing a cannonball in a pool,” said Shannon Curry, principal investigator of MAVEN at the Laboratory for Atmospheric and Space Physics at the University of Colorado Boulder and lead author of the study. “The cannonball, in this case, is the heavy ions crashing into the atmosphere really fast and splashing neutral atoms and molecules out.”
While scientists had previously found traces of evidence that this process was happening, they had never observed the process directly. The previous evidence came from looking at lighter and heavier isotopes of argon in the upper atmosphere of Mars. Lighter isotopes sit higher in the atmosphere than their heavier counterparts, and it was found that there were far fewer lighter isotopes than heavy argon isotopes in the Martian atmosphere. These lighter isotopes can only be removed by sputtering.
“It is like we found the ashes from a campfire,” said Curry. “But we wanted to see the actual fire, in this case sputtering, directly.”
To observe sputtering, the team needed simultaneous measurements in the right place at the right time from three instruments aboard the MAVEN spacecraft: the Solar Wind Ion Analyzer, the Magnetometer, and the Neutral Gas and Ion Mass Spectrometer. Additionally, the team needed measurements across the dayside and the nightside of the planet at low altitudes, which takes years to observe.
The combination of data from these instruments allowed scientists to make a new kind of map of sputtered argon in relation to the solar wind. This map revealed the presence of argon at high altitudes in the exact locations that the energetic particles crashed into the atmosphere and splashed out argon, showing sputtering in real time. The researchers also found that this process is happening at a rate four times higher than previously predicted and that this rate increases during solar storms.
The direct observation of sputtering confirms that the process was a primary source of atmospheric loss in Mars’ early history when the Sun’s activity was much stronger.
“These results establish sputtering’s role in the loss of Mars’ atmosphere and in determining the history of water on Mars,” said Curry.
The finding, published this week in Science Advances, is critical to scientists’ understanding of the conditions that allowed liquid water to exist on the Martian surface, and the implications that it has for habitability billions of years ago.
The MAVEN mission is part of NASA’s Mars Exploration Program portfolio. MAVEN’s principal investigator is based at the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder, which is also responsible for managing science operations and public outreach and communications. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the MAVEN mission. Lockheed Martin Space built the spacecraft and is responsible for mission operations. NASA’s Jet Propulsion Laboratory in Southern California provides navigation and Deep Space Network support.
More information on NASA’s MAVEN mission
By Willow Reed
Laboratory for Atmospheric and Space Physics, University of Colorado Boulder
Media Contacts:
Nancy N. Jones
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Karen Fox / Molly Wasser
Headquarters, Washington
202-358-1600
karen.c.fox@nasa.gov / molly.l.wasser@nasa.gov
karen.c.fox@nasa.gov / molly.l.wasser@nasa.gov
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Last Updated May 28, 2025 Related Terms
MAVEN (Mars Atmosphere and Volatile EvolutioN) Mars Planets View the full article
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By NASA
This NASA/ESA Hubble Space Telescope image features the remote galaxy HerS 020941.1+001557, which appears as a red arc that partially encircles a foreground elliptical galaxy.ESA/Hubble & NASA, H. Nayyeri, L. Marchetti, J. Lowenthal This NASA/ESA Hubble Space Telescope image offers us the chance to see a distant galaxy now some 19.5 billion light-years from Earth (but appearing as it did around 11 billion years ago, when the galaxy was 5.5 billion light-years away and began its trek to us through expanding space). Known as HerS 020941.1+001557, this remote galaxy appears as a red arc partially encircling a foreground elliptical galaxy located some 2.7 billion light-years away. Called SDSS J020941.27+001558.4, the elliptical galaxy appears as a bright dot at the center of the image with a broad haze of stars outward from its core. A third galaxy, called SDSS J020941.23+001600.7, seems to be intersecting part of the curving, red crescent of light created by the distant galaxy.
The alignment of this trio of galaxies creates a type of gravitational lens called an Einstein ring. Gravitational lenses occur when light from a very distant object bends (or is ‘lensed’) around a massive (or ‘lensing’) object located between us and the distant lensed galaxy. When the lensed object and the lensing object align, they create an Einstein ring. Einstein rings can appear as a full or partial circle of light around the foreground lensing object, depending on how precise the alignment is. The effects of this phenomenon are much too subtle to see on a local level but can become clearly observable when dealing with curvatures of light on enormous, astronomical scales.
Gravitational lenses not only bend and distort light from distant objects but magnify it as well. Here we see light from a distant galaxy following the curve of spacetime created by the elliptical galaxy’s mass. As the distant galaxy’s light passes through the gravitational lens, it is magnified and bent into a partial ring around the foreground galaxy, creating a distinctive Einstein ring shape.
The partial Einstein ring in this image is not only beautiful, but noteworthy. A citizen scientist identified this Einstein ring as part of the SPACE WARPS project that asked citizen scientists to search for gravitational lenses in images.
Text Credit: ESA/Hubble
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