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NASA’s Webb Reveals Smallest Asteroids Yet Found in Main Asteroid Belt
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By NASA
Explore Webb Webb News Latest News Latest Images Webb’s Blog Awards X (offsite – login reqd) Instagram (offsite – login reqd) Facebook (offsite- login reqd) Youtube (offsite) Overview About Who is James Webb? Fact Sheet Impacts+Benefits FAQ Science Overview and Goals Early Universe Galaxies Over Time Star Lifecycle Other Worlds Observatory Overview Launch Deployment Orbit Mirrors Sunshield Instrument: NIRCam Instrument: MIRI Instrument: NIRSpec Instrument: FGS/NIRISS Optical Telescope Element Backplane Spacecraft Bus Instrument Module Multimedia About Webb Images Images Videos What is Webb Observing? 3d Webb in 3d Solar System Podcasts Webb Image Sonifications Webb’s First Images Team International Team People Of Webb More For the Media For Scientists For Educators For Fun/Learning Since July 2022, NASA’s James Webb Space Telescope has been unwaveringly focused on our universe. With its unprecedented power to detect and analyze otherwise invisible infrared light, Webb is making observations that were once impossible, changing our view of the cosmos from the most distant galaxies to our own solar system.
Webb was built with the promise of revolutionizing astronomy, of rewriting the textbooks. And by any measure, it has more than lived up to the hype — exceeding expectations to a degree that scientists had not dared imagine. Since science operations began, Webb has completed more than 860 scientific programs, with one-quarter of its time dedicated to imaging and three-quarters to spectroscopy. In just three years, it has collected nearly 550 terabytes of data, yielding more than 1,600 research papers, with intriguing results too numerous to list and a host of new questions to answer.
Here are just a few noteworthy examples.
1. The universe evolved significantly faster than we previously thought.
Webb was specifically designed to observe “cosmic dawn,” a time during the first billion years of the universe when the first stars and galaxies were forming. What we expected to see were a few faint galaxies, hints of what would become the galaxies we see nearby.
Instead, Webb has revealed surprisingly bright galaxies that developed within 300 million years of the big bang; galaxies with black holes that seem far too massive for their age; and an infant Milky Way-type galaxy that existed when the universe was just 600 million years old. Webb has observed galaxies that already “turned off” and stopped forming stars within a billion years of the big bang, as well as those that developed quickly into modern-looking “grand design” spirals within 1.5 billion years.
Hundreds of millions of years might not seem quick for a growth spurt, but keep in mind that the universe formed in the big bang roughly 13.8 billion years ago. If you were to cram all of cosmic time into one year, the most distant of these galaxies would have matured within the first couple of weeks, rapidly forming multiple generations of stars and enriching the universe with the elements we see today.
Image: JADES deep field
A near-infrared image from NASA’s James Webb Space Telescope shows a region known as the JADES Deep Field. Tens of thousands of galaxies are visible in this tiny patch of sky, including Little Red Dots and hundreds of galaxies that existed more than 13.2 billion years ago, when the universe was less than 600 million years old. Webb also spotted roughly 80 ancient supernovae, many of which exploded when the universe was less than 2 billion years old. This is ten times more supernovae than had ever been discovered before in the early universe. Comparing these supernovae from the distant past with those in the more recent, nearby universe helps us understand how stars in these early times formed, lived, and died, seeding space with the elements for new generations of stars and their planets. NASA, ESA, CSA, STScI, JADES Collaboration 2. Deep space is scattered with enigmatic “Little Red Dots.”
Webb has revealed a new type of galaxy: a distant population of mysteriously compact, bright, red galaxies dubbed Little Red Dots. What makes Little Red Dots so bright and so red? Are they lit up by dense groupings of unusually bright stars or by gas spiraling into a supermassive black hole, or both? And whatever happened to them? Little Red Dots seem to have appeared in the universe around 600 million years after the big bang (13.2 billion years ago), and rapidly declined in number less than a billion years later. Did they evolve into something else? If so, how? Webb is probing Little Red Dots in more detail to answer these questions.
3. Pulsating stars and a triply lensed supernova are further evidence that the “Hubble Tension” is real.
How fast is the universe expanding? It’s hard to say because different ways of calculating the current expansion rate yield different results — a dilemma known as the Hubble Tension. Are these differences just a result of measurement errors, or is there something weird going on in the universe? So far, Webb data indicates that the Hubble Tension is not caused by measurement errors. Webb was able to distinguish pulsating stars from nearby stars in a crowded field, ensuring that the measurements weren’t contaminated by extra light. Webb also discovered a distant, gravitationally lensed supernova whose image appears in three different locations and at three different times during its explosion. Calculating the expansion rate based on the brightness of the supernova at these three different times provides an independent check on measurements made using other techniques. Until the matter of the Hubble Tension is settled, Webb will continue measuring different objects and exploring new methods.
4. Webb has found surprisingly rich and varied atmospheres on gas giants orbiting distant stars.
While NASA’s Hubble Space Telescope made the first detection of gases in the atmosphere of a gas giant exoplanet (a planet outside our solar system), Webb has taken studies to an entirely new level. Webb has revealed a rich cocktail of chemicals, including hydrogen sulfide, ammonia, carbon dioxide, methane, and sulfur dioxide — none of which had been clearly detected in an atmosphere outside our solar system before. Webb has also been able to examine exotic climates of gas giants as never before, detecting flakes of silica “snow” in the skies of the puffy, searing-hot gas giant WASP-17 b, for example, and measuring differences in temperature and cloud cover between the permanent morning and evening skies of WASP-39 b.
Image: Spectrum of WASP-107 b
A transmission spectrum of the “warm Neptune” exoplanet WASP-107 b captured by NASA’s Hubble and Webb space telescopes, shows clear evidence for water, carbon dioxide, carbon monoxide, methane, sulfur dioxide, and ammonia in the planet’s atmosphere. These measurements allowed researchers to estimate the interior temperature and mass of the core of the planet, as well as understand the chemistry and dynamics of the atmosphere. NASA, ESA, CSA, Ralf Crawford (STScI) 5. A rocky planet 40 light-years from Earth may have an atmosphere fed by gas bubbling up from its lava-covered surface.
Detecting, let alone analyzing, a thin layer of gas surrounding a small rocky planet is no easy feat, but Webb’s extraordinary ability to measure extremely subtle changes in the brightness of infrared light makes it possible. So far, Webb has been able to rule out significant atmosphere on a number of rocky planets, and has found tantalizing signs of carbon monoxide or carbon dioxide on 55 Cancri e, a lava world that orbits a Sun-like star. With findings like these, Webb is laying the groundwork for NASA’s future Habitable Worlds Observatory, which will be the first mission purpose-built to directly image and search for life on Earth-like planets around Sun-like stars.
6. Webb exposes the skeletal structure of nearby spiral galaxies in mesmerizing detail.
We already knew that galaxies are collections of stars, planets, dust, gas, dark matter, and black holes: cosmic cities where stars form, live, die, and are recycled into the next generation. But we had never been able to see the structure of a galaxy and the interactions between stars and their environment in such detail. Webb’s infrared vision reveals filaments of dust that trace the spiral arms, old star clusters that make up galactic cores, newly forming stars still encased in dense cocoons of glowing dust and gas, and clusters of hot young stars carving enormous cavities in the dust. It also elucidates how stellar winds and explosions actively reshape their galactic homes.
Image: PHANGS Phantom Galaxy (M74/NGC 628)
A near- to mid-infrared image from NASA’s James Webb Space Telescope highlights details in the complex structure of a nearby galaxy that are invisible to other telescopes. The image of NGC 628, also known as the Phantom Galaxy, shows spiral arms with lanes of warm dust (represented in red), knots of glowing gas (orange-yellow), and giant bubbles (black) carved by hot, young stars. The dust-free core of the galaxy is filled with older, cooler stars (blue). NASA, ESA, CSA, STScI, Janice Lee (STScI), Thomas Williams (Oxford), PHANGS team 7. It can be hard to tell the difference between a brown dwarf and a rogue planet.
Brown dwarfs form like stars, but are not dense or hot enough to fuse hydrogen in their cores like stars do. Rogue planets form like other planets, but have been ejected from their system and no longer orbit a star. Webb has spotted hundreds of brown-dwarf-like objects in the Milky Way, and has even detected some candidates in a neighboring galaxy. But some of these objects are so small — just a few times the mass of Jupiter — that it is hard to figure out how they formed. Are they free-floating gas giant planets instead? What is the least amount of material needed to form a brown dwarf or a star? We’re not sure yet, but thanks to three years of Webb observations, we now know there is a continuum of objects from planets to brown dwarfs to stars.
8. Some planets might be able to survive the death of their star.
When a star like our Sun dies, it swells up to form a red giant large enough to engulf nearby planets. It then sheds its outer layers, leaving behind a super-hot core known as a white dwarf. Is there a safe distance that planets can survive this process? Webb might have found some planets orbiting white dwarfs. If these candidates are confirmed, it would mean that it is possible for planets to survive the death of their star, remaining in orbit around the slowly cooling stellar ember.
9. Saturn’s water supply is fed by a giant fountain of vapor spewing from Enceladus.
Among the icy “ocean worlds” of our solar system, Saturn’s moon Enceladus might be the most intriguing. NASA’s Cassini mission first detected water plumes coming out of its southern pole. But only Webb could reveal the plume’s true scale as a vast cloud spanning more than 6,000 miles, about 20 times wider than Enceladus itself. This water spreads out into a donut-shaped torus encircling Saturn beyond the rings that are visible in backyard telescopes. While a fraction of the water stays in that ring, the majority of it spreads throughout the Saturnian system, even raining down onto the planet itself. Webb’s unique observations of rings, auroras, clouds, winds, ices, gases, and other materials and phenomena in the solar system are helping us better understand what our cosmic neighborhood is made of and how it has changed over time.
Video: Water plume and torus from Enceladus
A combination of images and spectra captured by NASA’s James Webb Space Telescope show a giant plume of water jetting out from the south pole of Saturn’s moon Enceladus, creating a donut-shaped ring of water around the planet.
Credit: NASA, ESA, CSA, G. Villanueva (NASA’s Goddard Space Flight Center), A. Pagan (STScI), L. Hustak (STScI) 10. Webb can size up asteroids that may be headed for Earth.
In 2024 astronomers discovered an asteroid that, based on preliminary calculations, had a chance of hitting Earth. Such potentially hazardous asteroids become an immediate focus of attention, and Webb was uniquely able to measure the object, which turned out to be the size of a 15-story building. While this particular asteroid is no longer considered a threat to Earth, the study demonstrated Webb’s ability to assess the hazard.
Webb also provided support for NASA’s Double Asteroid Redirection Test (DART) mission, which deliberately smashed into the Didymos binary asteroid system, showing that a planned impact could deflect an asteroid on a collision course with Earth. Both Webb and Hubble observed the impact, serving witness to the resulting spray of material that was ejected. Webb’s spectroscopic observations of the system confirmed that the composition of the asteroids is probably typical of those that could threaten Earth.
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In just three years of operations, Webb has brought the distant universe into focus, revealing unexpectedly bright and numerous galaxies. It has unveiled new stars in their dusty cocoons, remains of exploded stars, and skeletons of entire galaxies. It has studied weather on gas giants, and hunted for atmospheres on rocky planets. And it has provided new insights into the residents of our own solar system.
But this is only the beginning. Engineers estimate that Webb has enough fuel to continue observing for at least 20 more years, giving us the opportunity to answer additional questions, pursue new mysteries, and put together more pieces of the cosmic puzzle.
For example: What were the very first stars like? Did stars form differently in the early universe? Do we even know how galaxies form? How do stars, dust, and supermassive black holes affect each other? What can merging galaxy clusters tell us about the nature of dark matter? How do collisions, bursts of stellar radiation, and migration of icy pebbles affect planet-forming disks? Can atmospheres survive on rocky worlds orbiting active red dwarf stars? Is Uranus’s moon Ariel an ocean world?
As with any scientific endeavor, every answer raises more questions, and Webb has shown that its investigative power is unmatched. Demand for observing time on Webb is at an all-time high, greater than any other telescope in history, on the ground or in space. What new findings await?
By Dr. Macarena Garcia Marin and Margaret W. Carruthers, Space Telescope Science Institute, Baltimore, Maryland
Media Contacts
Laura Betz – laura.e.betz@nasa.gov
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Christine Pulliam – cpulliam@stsci.edu
Space Telescope Science Institute, Baltimore, Md.
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Last Updated Jul 02, 2025 Editor Marty McCoy Contact Laura Betz laura.e.betz@nasa.gov Related Terms
James Webb Space Telescope (JWST) Astrophysics Black Holes Brown Dwarfs Exoplanet Science Exoplanets Galaxies Galaxies, Stars, & Black Holes Goddard Space Flight Center Nebulae Science & Research Star-forming Nebulae Stars Studying Exoplanets The Universe View the full article
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By European Space Agency
Asteroid 2024 YR4 made headlines earlier this year when its probability of impacting Earth in 2032 rose as high as 3%. While an Earth impact has now been ruled out, the asteroid’s story continues.
The final glimpse of the asteroid as it faded out of view of humankind’s most powerful telescopes left it with a 4% chance of colliding with the Moon on 22 December 2032.
The likelihood of a lunar impact will now remain stable until the asteroid returns to view in mid-2028. In this FAQ, find out why we are left with this lingering uncertainty and how ESA's planned NEOMIR space telescope will help us avoid similar situations in the future.
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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 European Space Agency
Astronomers using the NASA/ESA/CSA James Webb Space Telescope have captured compelling evidence of a planet with a mass similar to Saturn orbiting the young nearby star TWA 7.
If confirmed, this would represent Webb’s first direct image discovery of a planet, and the lightest planet ever seen with this technique.
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