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Asteroid 2024 YR4 no longer poses significant impact risk
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By NASA
5 min read
Close-Up Views of NASA’s DART Impact to Inform Planetary Defense
Photos taken by the Italian LICIACube, short for the LICIA Cubesat for Imaging of Asteroids. These offer the closest, most detailed observations of NASA’s DART (Double Asteroid Redirection Test) impact aftermath to date. The photo on the left was taken roughly 2 minutes and 40 seconds after impact, as the satellite flew past the Didymos system. The photo on the right was taken 20 seconds later, as LICIACube was leaving the scene. The larger body, near the top of each image is Didymos. The smaller body in the lower half of each image is Dimorphos, enveloped by the cloud of rocky debris created by DART’s impact. NASA/ASI/University of Maryland On Sept. 11, 2022, engineers at a flight control center in Turin, Italy, sent a radio signal into deep space. Its destination was NASA’s DART (Double Asteroid Redirection Test) spacecraft flying toward an asteroid more than 5 million miles away.
The message prompted the spacecraft to execute a series of pre-programmed commands that caused a small, shoebox-sized satellite contributed by the Italian Space Agency (ASI), called LICIACube, to detach from DART.
Fifteen days later, when DART’s journey ended in an intentional head-on collision with near-Earth asteroid Dimorphos, LICIACube flew past the asteroid to snap a series of photos, providing researchers with the only on-site observations of the world’s first demonstration of an asteroid deflection.
After analyzing LICIACube’s images, NASA and ASI scientists report on Aug. 21 in the Planetary Science Journal that an estimated 35.3 million pounds (16 million kilograms) of dust and rocks spewed from the asteroid as a result of the crash, refining previous estimates that were based on data from ground and space-based observations.
While the debris shed from the asteroid amounted to less than 0.5% of its total mass, it was still 30,000 times greater than the mass of the spacecraft. The impact of the debris on Dimorphos’ trajectory was dramatic: shortly after the collision, the DART team determined that the flying rubble gave Dimorphos a shove several times stronger than the hit from the spacecraft itself.
“The plume of material released from the asteroid was like a short burst from a rocket engine,” said Ramin Lolachi, a research scientist who led the study from NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
The important takeaway from the DART mission is that a small, lightweight spacecraft can dramatically alter the path of an asteroid of similar size and composition to Dimorphos, which is a “rubble-pile” asteroid — or a loose, porous collection of rocky material bound together weakly by gravity.
“We expect that a lot of near-Earth asteroids have a similar structure to Dimorphos,” said Dave Glenar, a planetary scientist at the University of Maryland, Baltimore County, who participated in the study. “So, this extra push from the debris plume is critical to consider when building future spacecraft to deflect asteroids from Earth.”
The tail of material that formed behind Dimorphos was prominent almost 12 days after the DART impact, giving the asteroid a comet-like appearance, as seen in this image captured by NASA’s Hubble Space Telescope in October 2022. Hubble’s observations were made from roughly 6.8 million miles away. NASA, ESA, STScI, Jian-Yang Li (PSI); Image Processing: Joseph DePasquale DART’s Star Witness
NASA chose Dimorphos, which poses no threat to Earth, as the mission target due to its relationship with another, larger asteroid named Didymos. Dimorphos orbits Didymos in a binary asteroid system, much like the Moon orbits Earth. Critically, the pair’s position relative to Earth allowed astronomers to measure the duration of the moonlet’s orbit before and after the collision.
Ground and space-based observations revealed that DART shortened Dimorphos’ orbit by 33 minutes. But these long-range observations, made from 6.8 million miles (10.9 million kilometers) away, were too distant to support a detailed study of the impact debris. That was LICIACube’s job.
After DART’s impact, LICIACube had just 60 seconds to make its most critical observations. Barreling past the asteroid at 15,000 miles (21,140 kilometers) per hour, the spacecraft took a snapshot of the debris roughly once every three seconds. Its closest image was taken just 53 miles (85.3 km) from Dimorphos’ surface.
The short distance between LICIACube and Dimorphos provided a unique advantage, allowing the cubesat to capture detailed images of the dusty debris from multiple angles.
The research team studied a series of 18 LICIAcube images. The first images in the sequence showed LICIACube’s head-on approach. From this angle, the plume was brightly illuminated by direct sunlight. As the spacecraft glided past the asteroid, its camera pivoted to keep the plume in view.
This animated series of images was taken by a camera aboard LICIACube 2 to 3 minutes after DART crashed into Dimorphos. As LICIACube made its way past the binary pair of asteroids Didymos, the larger one on top, and Dimorphos, the object at the bottom. The satellite’s viewing angle changed rapidly during its flyby of Dimorphos, allowing scientists o get a comprehensive view of the impact plume from a series of angles. ASI/University of Maryland/Tony Farnham/Nathan Marder As LICIACube looked back at the asteroid, sunlight filtered through the dense cloud of debris, and the plume’s brightness faded. This suggested the plume was made of mostly large particles — about a millimeter or more across — which reflect less light than tiny dust grains.
Since the innermost parts of the plume were so thick with debris that they were completely opaque, the scientists used models to estimate the number of particles that were hidden from view. Data from other rubble-pile asteroids, including pieces of Bennu delivered to Earth in 2023 by NASA’s OSIRIS-REx spacecraft, and laboratory experiments helped refine the estimate.
“We estimated that this hidden material accounted for almost 45% of the plume’s total mass,” said Timothy Stubbs, a planetary scientist at NASA Goddard who was involved with the study.
While DART showed that a high-speed collision with a spacecraft can change an asteroid’s trajectory, Stubbs and his colleagues note that different asteroid types, such as those made of stronger, more tightly packed material, might respond differently to a DART-like impact. “Every time we interact with an asteroid, we find something that surprises us, so there’s a lot more work to do,” said Stubbs. “But DART is a big step forward for planetary defense.”
The Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, managed the DART mission and operated the spacecraft for NASA’s Planetary Defense Coordination Office as a project of the agency’s Planetary Missions Program Office.
By Nathan Marder, nathan.marder@nasa.gov
NASA’s Goddard Space Flight Center, Greenbelt, Md.
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Last Updated Aug 21, 2025 Related Terms
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By European Space Agency
ESA’s Hera mission has captured images of asteroids (1126) Otero and (18805) Kellyday. Though distant and faint, the early observations serve as both a successful instrument test and a demonstration of agile spacecraft operations that could prove useful for planetary defence.
Hera is currently travelling through space on its way to a binary asteroid system. In 2022, NASA’s DART spacecraft impacted the asteroid Dimorphos, changing its orbit around the larger asteroid Didymos. Now, Hera is returning to the system to help turn asteroid deflection into a reliable technique for planetary defence.
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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 European Space Agency
Image: This image shows Webb’s recent observation of the asteroid 2024 YR4 using both its Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI). Data from NIRCam shows reflected light, while the MIRI observations show thermal light.
On 8 March 2025, the NASA/ESA/CSA James Webb Space Telescope turned its watchful eye toward asteroid 2024 YR4, which we now know poses no significant threat to Earth in 2032 and beyond.
This is the smallest object targeted by Webb to date, and one of the smallest objects to have its size directly measured.
Observations were taken to study the thermal properties of 2024 YR4, including how quickly it heats up and cools down and how hot it is at its current distance from the Sun. These measurements indicate that this asteroid does not share properties observed in larger asteroids. This is likely a combination of its fast spin and lack of fine-grained sand on its surface. Further research is needed, however this is considered consistent with a surface dominated by rocks that are roughly fist-sized or larger.
Asteroid 2024 YR4 was recently under close watch by the team at ESA's Near Earth Objects Coordination Centre, located in Italy. Planetary defence experts from the Agency's Space Safety programme worked with NASA and the international asteroid community to closely watch this object and refine its orbit, which was eventually determined to not pose a risk of Earth impact. Read details on this unusual campaign via ESA's Rocket Science blog and in news articles here and here.
Webb’s observations indicate that the asteroid measures roughly 60 meters (comparable to the height of a 15-story building).
The new observations from Webb not only provide unique information about 2024 YR4’s size, but can also complement ground-based observations of the object's position to help improve our understanding of the object’s orbit and future trajectory.
Note: This post highlights data from Webb science in progress, which has not yet been through the peer-review process.
[Image description: A collage of three images showing the black expanse of space. Two-thirds of the collage is taken up by the black background sprinkled with small, blurry galaxies in orange, blue, and white. There are two images in a column at the right side of the collage. On the right side of the main image, not far from the top, a very faint dot is outlined with a white square. At the right, there are two zoomed in views of this area. The top box is labeled NIRCam and shows a fuzzy dot at the center of the inset. The bottom box is labeled MIRI and shows a fuzzy pinkish dot.]
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By NASA
6 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
Risks Concept Risk is inherent in human spaceflight. However, specific risks can and should be understood, managed, and mitigated to reduce threats posed to astronauts. Risk management in the context of human spaceflight can be viewed as a trade-based system. The relevant evidence in life sciences, medicine, and engineering is tracked and evaluated to identify ways to minimize overall risk to the astronauts and to ensure mission success. The Human System Risk Board (HSRB) manages the process by which scientific evidence is utilized to establish and reassess the postures of the various risks to the Human System during all of the various types of existing or anticipated crewed missions. The HSRB operates as part of the Health and Medical Technical Authority of the Office of the Chief Health and Medical Officer of NASA via the JSC Chief Medical Officer.
The HSRB approaches to human system risks is analogous to the approach the engineering profession takes with its Failure Mode and Effects Analysis in that a process is utilized to identify and address potential problems, or failures to reduce their likelihood and severity. In the context of risks to the human system, the HSRB considers eight missions which different in their destinations and durations (known as Design Reference Missions [DRM]) to further refine the context of the risks. With each DRM a likelihood and consequence are assigned to each risk which is adjusted scientific evidence is accumulated and understanding of the risk is enhanced, and mitigations become available or are advanced.
Human System Risks This framework enables the principles of Continuous Risk Management and Risk Informed Decision Making (RIDM) to be applied in an ongoing fashion to the challenges posed by Human System Risks. Using this framework consistently across the 29 risks allows management to see where risks need additional research or technology development to be mitigated or monitored and for the identification of new risks and concerns. Further information on the implementation of the risk management process can be found in the following documents:
Human System Risk Management Plan – JSC-66705 NASA Health and Medical Technical Authority (HMTA) Implementation – NPR 7120.11A NASA Space Flight Program and Project Management Requirements – NPR 7120.5 Human System Risk Board Management Office
The HSRB Risk Management Office governs the execution of the Human System Risk management process in support of the HSRB. It is led by the HSRB Chair, who is also referred to as the Risk Manager.
Risk Custodian Teams
Along with the Human System Risk Manager, a team of risk custodians (a researcher, an operational researcher or physician, and an epidemiologist, who each have specific expertise) works together to understand and synthesize scientific and operational evidence in the context of spaceflight, identify and evaluate metrics for each risk in order to communicate the risk posture to the agency.
Directed Acyclic Graphs
Summary
The HSRB uses Directed Acyclic Graphs (DAG), a type of causal diagramming, as visual tools to create a shared understanding of the risks, improve communication among those stakeholders, and enable the creation of a composite risk network that is vetted by members of the NASA community and configuration managed (Antonsen et al., NASA/TM– 20220006812). The knowledge captured is the Human Health and Performance community’s knowledge about the causal flow of a human system risk, and the relationships that exist between the contributing factors to that risk.
DAGs are:
Intended to improve communication between: Managers and subject matter experts who need to discuss human system risks Subject matter experts in different disciplines where human system risks interact with one another in a potentially cumulative fashion Visual representations of known or suspected relationships Directed – the relationship flows in one direction between any two nodes Acyclic – cycles in the graph are not allowed Example of a Directed Acyclic Graph. This is a simplified illustration of how and the individual, the crew, and the system contribute to the likelihood of successful task performance in a mission. Individual readiness is affected by many of the health and performance-oriented risks followed by the HSRB, but the readiness of any individual crew is complemented by the team and the system that the crew works within. Failures of task performance may lead to loss of mission objectives if severe.NASA View Larger (Example of a Directed Acyclic Graph) Image
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At NASA, the Human System Risks have historically been conceptualized as deriving from five Hazards present in the spaceflight environment. These are: altered gravity, isolation and confinement, radiation, a hostile closed environment, and distance from Earth. These Hazards are aspects of the spaceflight environment that are encountered when someone is launched into space and therefore are the starting point for causal diagramming of spaceflight-related risk issues for the HSRB.
These Hazards are often interpreted in relation to physiologic changes that occur in humans as a result of the exposure; however, interaction between human crew (behavioral health and performance), which may be degraded due to the spaceflight environment – and the vehicle and mission systems that the crew must operate – can also be influenced by these Hazards.
Each Human System Risk DAG is intended to show the causal flow of risk from Hazards to Mission Level Outcomes. As such, the structure of each DAG starts with at least one Hazard and ends with at least one of the pre-defined Mission Level Outcomes. In between are the nodes and edges of the causal flow diagrams that are relevant to the Risk under consideration. These are called ‘contributing factors’ in the HSRB terminology, and include countermeasures, medical conditions, and other Human System Risks. A graph data structure is composed of a set of vertices (nodes), and a set of edges (links). Each edge represents a relationship between two nodes. There can be two types of relationships between nodes: directed and undirected. For example, if an edge exists between two nodes A and B and the edge is undirected, it is represented as A–B, (no arrow). If the edge were directed, for example from A to B, then this is represented with an arrow (A->B). Each directed arrow connecting one node to another on a DAG indicates a claim of causality. A directed graph can potentially contain a cycle, meaning that, from a specific node, there exists a path that would eventually return to that node. A directed graph that has no cycles is known as acyclic. Thus, a graph with directed links and no cycles is a DAG. DAGs are a type of network diagram that represent causality in a visual format.
DAGs are updated with the regular Human System Risk updates generally every 1-2 years. Approved DAGs can be found in the NASA/TP 20220015709 below or broken down under each Human System Risk.
Documents
Directed Acyclic Graph Guidance Documentation – NASA/TM 20220006812 Directed Acyclic Graphs: A Tool for Understanding the NASA Human Spaceflight System Risks – NASA/TP 20220015709 Publications
npj Microgravity – Causal diagramming for assessing human
system risk in spaceflight
Apr 22, 2024
PDF (3.09 MB)
npj Microgravity –
Levels of evidence for human system risk
evaluation
Apr 22, 2024
PDF (2.47 MB)
npj Microgravity –
Updates to the NASA human system risk management process
for space exploration
Apr 22, 2024
PDF (2.24 MB)
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