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Asteroid 2024 YR4 no longer poses significant impact risk
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By NASA
1 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
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By European Space Agency
Video: 00:02:14 On 12 March 2025, ESA’s Hera spacecraft soared just 5000 km above Mars and passed within 300 km of its distant moon, Deimos. Captured by Hera’s 1020x1020 pixel Asteroid Framing Camera, this video sequence offers a rare view of the red planet and its enigmatic moon. The original greyscale images have been colour-enhanced based on known surface features.
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By NASA
NASA’s Lucy spacecraft is 6 days and less than 50 million miles (80 million km) away from its second close encounter with an asteroid; this time, the small main belt asteroid Donaldjohanson.
Download high-resolution video and images from NASA’s Scientific Visualization Studio.
NASA/Dan Gallagher This upcoming event represents a comprehensive “dress rehearsal” for Lucy’s main mission over the next decade: the exploration of multiple Trojan asteroids that share Jupiter’s orbit around the Sun. Lucy’s first asteroid encounter – a flyby of the tiny main belt asteroid Dinkinesh and its satellite, Selam, on Nov. 1, 2023 – provided the team with an opportunity for a systems test that they will be building on during the upcoming flyby.
Lucy’s closest approach to Donaldjohanson will occur at 1:51pm EDT on April 20, at a distance of 596 miles (960 km). About 30 minutes before closest approach, Lucy will orient itself to track the asteroid, during which its high-gain antenna will turn away from Earth, suspending communication. Guided by its terminal tracking system, Lucy will autonomously rotate to keep Donaldjohanson in view. As it does this, Lucy will carry out a more complicated observing sequence than was used at Dinkinesh. All three science instruments – the high-resolution greyscale imager called L’LORRI, the color imager and infrared spectrometer called L’Ralph, and the far infrared spectrometer called L’TES – will carry out observation sequences very similar to the ones that will occur at the Trojan asteroids.
However, unlike with Dinkinesh, Lucy will stop tracking Donaldjohanson 40 seconds before the closest approach to protect its sensitive instruments from intense sunlight.
“If you were sitting on the asteroid watching the Lucy spacecraft approaching, you would have to shield your eyes staring at the Sun while waiting for Lucy to emerge from the glare. After Lucy passes the asteroid, the positions will be reversed, so we have to shield the instruments in the same way,” said encounter phase lead Michael Vincent of Southwest Research Institute (SwRI) in Boulder, Colorado. “These instruments are designed to photograph objects illuminated by sunlight 25 times dimmer than at Earth, so looking toward the Sun could damage our cameras.”
Fortunately, this is the only one of Lucy’s seven asteroid encounters with this challenging geometry. During the Trojan encounters, as with Dinkinesh, the spacecraft will be able to collect data throughout the entire encounter.
After closest approach, the spacecraft will “pitch back,” reorienting its solar arrays back toward the Sun. Approximately an hour later, the spacecraft will re-establish communication with Earth.
“One of the weird things to wrap your brain around with these deep space missions is how slow the speed of light is,” continued Vincent. “Lucy is 12.5 light minutes away from Earth, meaning it takes that long for any signal we send to reach the spacecraft. Then it takes another 12.5 minutes before we get Lucy’s response telling us we were heard. So, when we command the data playback after closest approach, it takes 25 minutes from when we ask to see the pictures before we get any of them to the ground.”
Once the spacecraft’s health is confirmed, engineers will command Lucy to transmit the science data from the encounter back to Earth, which is a process that will take several days.
Donaldjohanson is a fragment from a collision 150 million years ago, making it one of the youngest main belt asteroids ever visited by a spacecraft.
“Every asteroid has a different story to tell, and these stories weave together to paint the history of our solar system,” said Tom Statler, Lucy mission program scientist at NASA Headquarters in Washington. “The fact that each new asteroid we visit knocks our socks off means we’re only beginning to understand the depth and richness of that history. Telescopic observations are hinting that Donaldjohanson is going to have an interesting story, and I’m fully expecting to be surprised – again.”
NASA’s Goddard Space Flight Center in Greenbelt, Maryland, designed and built the L’Ralph instrument and provides overall mission management, systems engineering and safety and mission assurance for Lucy. Hal Levison of SwRI’s office in Boulder, Colorado, is the principal investigator. SwRI, headquartered in San Antonio, also leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space in Littleton, Colorado, built the spacecraft, designed the original orbital trajectory and provides flight operations. Goddard and KinetX Aerospace are responsible for navigating the Lucy spacecraft. The Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, designed and built the L’LORRI (Lucy Long Range Reconnaissance Imager) instrument. Arizona State University in Tempe, Arizona, designed and build the L’TES (Lucy Thermal Emission Spectrometer) instrument. Lucy is the thirteenth mission in NASA’s Discovery Program, which is managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama.
By Katherine Kretke, Southwest Research Institute
Media Contact:
Karen Fox / Molly Wasser
Headquarters, Washington
202-358-1600
karen.c.fox@nasa.gov / molly.l.wasser@nasa.gov
Nancy N. Jones
NASA’s Goddard Space Flight Center, Greenbelt, Md.
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Last Updated Apr 14, 2025 EditorMadison OlsonContactNancy N. Jonesnancy.n.jones@nasa.govLocationGoddard Space Flight Center Related Terms
Lucy Goddard Space Flight Center Planetary Science Explore More
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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
5 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
In-person participants (L-R) – Back row: Jason Lytle, Stuart Lee, Eric Bershad, Ashot Sargsyan, Aaron Everson, Philip Wells, Sergi Vaquer Araujo, Steven Grover, John A. Heit, Mehdi Shishehbor, Laura Bostick; Middle row: Sarah Childress Taoufik, Stephan Moll, Brandon Macias, Kristin Coffey, Ann-Kathrin Vlacil, Dave Francisco; Front row: James Pavela, Doug Ebert, Kathleen McMonigal, Esther Kim, Emma Hwang; Not pictured: Tyson Brunstetter, J. D. Polk
Online participants: Stephen Alamo, Mark Crowther, Steven Nissen, Mark Rosenberg, Jeffrey Weitz, R. Eugene Zierler, Serena Aunon, Tina Bayuse, Laura Beachy, Becky Brocato, Daniel Buckland, Jackie Charvat, Diana Cruz Topete, Quinn Dufurrena, Robert Haddon, Joanne Kaouk, Kim Lowe, Steve Laurie, Karina Marshall-Goebel, Sara Mason, Shannan Moynihan, James Pattarini, Devan Petersen, Ruth Reitzel, Donna Roberts, Lucia Roccaro, Mike Stenger, Terry Taddeo, Gavin Travers, Mary Van Baalen, Liz WarrenNASA In October 2024, NASA’s Office of the Chief Health and Medical Officer (OCHMO) initiated a working group to review the status and progress of research and clinical activities intended to mitigate the risk of venous thromboembolism (VTE) during spaceflight. The working group took place over two days at NASA’s Johnson Space Center; a second meeting on the topic was held in December 2024 at the European Space Agency (ESA) facility in Cologne, Germany.
Read More about the Risk of VTE The working group was assembled from internal NASA subject matter experts (SMEs), the NASA OCHMO Standards Team, NASA and ESA stakeholders, and external SMEs, including physicians and medical professionals from leading universities and medical centers in the United States and Canada.
Background
Spaceflight Venous Thrombosis (SVT)
Spaceflight Venous Thrombosis (SVT) refers to a phenomenon experienced during spaceflight in which a thrombus (blood clot) forms in the internal jugular vein (and/or associated vasculature) that may be symptomatic (thrombus accompanied by, but not limited to, visible internal jugular vein swelling, facial edema beyond “nominal” spaceflight adaptation, eyelid edema, and/or headache) or asymptomatic. Obstructive thrombi have been identified in a very small number of crewmembers, as shown in the figure below.
Note that the figure below is for illustrative purposes only; locations are approximate, and size is not to scale.
Approximate location of identified thrombi in crewmembers.Source: Modified from Cerebral Sinus Venous Thrombosis – University of Colorado Denver With treatment, crewmembers were able to complete their mission, and anticoagulants were discontinued several days prior to landing to minimize the risk of bleeding in the event of a traumatic injury. Some thromboses completely resolved post landing, and some required additional treatment.
Pathophysiology of Venous Thromboembolism (VTE)
The proposed pathogenesis of VTE is referred to as Virchow’s triad and suggests that VTE occurs as the result of:
Alterations in blood flow (i.e., stasis), Vascular endothelial injury/changes, and/or, Alterations in the constituents of the blood leading to hypercoagulability (i.e., hereditary predisposition or acquired hypercoagulability). Note: pathophysiology are the changes that occur during a disease process; hypercoagulability is the increased tendency to develop blood to clots.
The Virchow’s triad of risk factors for venous thrombosis.Bouchnita, 2017 Blood stasis, or venous stasis, refers to a condition in which the blood flow in the veins slows down which leads to pooling in the veins. This slowing of the blood may be due to vein valves becoming damaged or weak, immobility, and/or the absence of muscular contractions. Associated symptoms include swelling, skin changes, varicose veins, and slow-healing sores or ulcers. In terrestrial medicine, venous thrombosis is typically caused by damaged or weakened vein valves, which can be due to many factors, including aging, blood clots, varicose veins, obesity, pregnancy, sedentary lifestyle, estrogen use, and hereditary predisposition.
Spaceflight Considerations
Altered Venous Blood Flow and Spaceflight Associated Neuro-ocular Syndrome
In addition to the terrestrial risk factors of VTE, there are physiological changes associated with spaceflight that are hypothesized to potentially play a role in the development of VTE in weightlessness. Specifically, researchers have explored the effects of the microgravity environment and subsequent observed headward fluid shifts that occur, and the potential impact on blood flow. Crewmembers onboard the International Space Station (ISS) experience weightlessness due to the microgravity environment and thus experience a sustained redistribution of bodily fluids from the legs toward the head. The prolonged headward fluid shifts during weightlessness results in facial puffiness, decreased leg volume, increased cardiac stroke volume, and decreased plasma volume.
Crewmembers have also experienced altered blood flow during spaceflight, including retrograde venous blood flow (RVBF) (the backflow of venous blood towards the brain) or stasis (a stoppage or slowdown in the flow of blood). While the causes of the observed stasis and retrograde blood flow in spaceflight participants is not well understood, the potential clinical significance of the role it may have in the development of thrombus formation warrants further investigation.
Doppler imaging of a retrograde flow in the left internal jugular vein.Yan & Seow, 2009 Other physiological concerns affected by fluid shifts are being studied to consider if any relation to VTE exists. Chronic weightlessness can cause bodily fluids such as blood and cerebrospinal fluid to move toward the head, which can lead to optic nerve swelling, folds in the retina, flattening of the back of the eye, and swelling in the brain. This collection of eye and brain changes is called “spaceflight associated neuro-ocular syndrome,” or SANS. Some astronauts only experience mild changes in space, while others have clinically significant outcomes. The long-term health outcome from these changes is unknown but actively being investigated. The risk of developing SANS is higher during longer-duration missions and remains a top research priority for scientists ahead of a Mars mission.
Conclusions and Further Work
Based on expert opinion and the assessment of the risk factors for thrombosis, an algorithm was developed to provide guidance for in-mission assessment and treatment of thrombus formation in weightlessness. The algorithm is based on early in-flight ultrasound testing to determine the flow characteristic of the left internal jugular vein and associated vasculature.
NASA Working Group Recommendations
The working group recommended several areas for further investigation to assess feasibility and potential to mitigate the risk of thrombosis in spaceflight:
Improved detection capabilities to identify when a thrombus has formed in-flight, Pathophysiology/factors leading to thrombi formation during spaceflight, Countermeasures and treatment
For more information on the working group meeting and a complete list of references, please see the Risk of Venous Thromboembolism (VTE) During Spaceflight Summary Report.
Risk of Venous Thromboembolism (VTE) During Spaceflight Summary Report Share
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Last Updated Mar 14, 2025 EditorKim Lowe Related Terms
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