2024 YR₄ is an asteroid that is classified as an Apollo-type (Earth-crossing) near-Earth object with an estimated diameter of 40 to 90 metres (130 to 300 ft), which for most of February 2025 had an impact rating of 3 on the Torino scale. As of 24 February 2025, it has a rating of 0 on the Torino scale, with a 1-in-59,000 (0.0017%) chance of impacting Earth on 22 December 2032,^[7] and a rating of −3.45 on the Palermo scale, corresponding to an impact hazard 0.08% of the background level.^[7] The uncertainty region for the path of its potential impact in 2032 is 560,000 thousand km (350,000 thousand mi) wide.^[13] The nominal approach on 22 December 2032 has the asteroid passing closer to the Moon than it does to Earth,^[3] but the 3-sigma uncertainty in the distances is less than a lunar distance (as of February 2025).

The asteroid was discovered by the Chilean station of the Asteroid Terrestrial-impact Last Alert System (ATLAS) at Río Hurtado on 27 December 2024.^[2][1] When additional observations suggested it had an impact probability of over 1%, it triggered the first step in planetary-defense responses, which prompted several major telescopes to gather data about the asteroid and led United Nations–endorsed space agencies to begin planning asteroid threat mitigation.^[14][15][16]

The asteroid made a close approach to Earth at a distance of 828,800 kilometres (515,000 miles; 2.156 lunar distances) on 25 December 2024, two days before its discovery, and is now moving away. Its next close approach will take place on 17 December 2028.^[3] From early April 2025 to June 2028, the asteroid is expected to be too distant for ground-based telescopes to observe. However, space-based infrared telescopes could continue monitoring it during some of this period;^[16][17] for example, the James Webb Space Telescope is scheduled to observe it between March and May 2025.^[18] Preliminary analysis of spectral and photometric time series suggests that 2024 YR₄ is a stony S-type (most likely), L-type or K-type asteroid, with a rotation period of approximately 19.5 minutes.^[8] A number of known asteroids, including other virtual impactors,^[a] follow orbits somewhat consistent with that of 2024 YR₄.^[19]

The asteroid's provisional designation as a minor planet, "2024 YR₄", was assigned by the Minor Planet Center when its discovery was announced on 27 December 2024.^[2] 2024 indicates the discovery year, the first letter, "Y", indicates that the asteroid was discovered in the second half-month of December (16 to 31 December) of that year, and "R₄" indicates that it was the 117th provisional designation to be assigned in that half-month.^[20]

The diameter of 2024 YR₄ has not been measured, but it can be estimated from its brightness (absolute magnitude) using a range of plausible values for its surface reflectivity (geometric albedo).^[7][21] If 2024 YR₄ reflects between 5% and 25% of visible light, as does the vast majority of asteroids with a measured albedo, then its diameter is between 40 and 90 m (130 and 300 ft).^[6] An estimate by NASA places its diameter at 55 m (180 ft) for an assumed geometric albedo of 0.154.^[7] These estimates make 2024 YR₄ around the same size as the asteroid that caused the 1908 Tunguska event or the iron–nickel asteroid that created the Meteor Crater in Arizona 50,000 years ago.^[21] 2024 YR₄ is significantly smaller than Dimorphos, the impact target of NASA's Double Asteroid Redirection Test (DART) in 2022. The diameter and albedo of 2024 YR₄ could be further constrained with thermal infrared observations, radar observations, an occultation of a star, or direct imaging by a spacecraft.^[17]

The mass and density of 2024 YR₄ have not been measured, but the mass can be loosely estimated with an assumed density and assumed diameter. Assuming a density of 2.6 g/cm³ (1.5 oz/cu in),^[22] which is within the density range for stony asteroids such as 243 Ida,^[23] with an assumed diameter of 55 m (180 ft), the Sentry risk table estimates a mass of 2.2×10⁸ kg (4.9×10⁸ lb).^[7] Both the assumed density and the inferred diameter contribute large uncertainties to the mass estimate, with the latter dominant as the volume of the asteroid depends on the cube of the diameter.

Preliminary spectroscopic analysis from the Gran Telescopio Canarias and Lowell Discovery Telescope suggests that 2024 YR₄ is either an S-type asteroid (17% of the asteroid population), an L-type asteroid, or a K-type asteroid, all of which point to a stony composition.^[10][8][b]

Photometric observations by the Very Large Telescope (VLT) and the La Silla Observatory's 1.54-metre (5.1 ft) telescope indicate 2024 YR₄ has a rotation period near 19.5 minutes.^[10][9] This is a relatively fast rotation period for an asteroid, although it is not fast enough to rule out a rubble pile structure for 2024 YR₄.^[8] The brightness of 2024 YR₄ varies by 0.42 magnitudes as it rotates, indicating it has an elongated shape with its longest equatorial length being at least 1.4 times that of its shortest equatorial length.^[9][8] The VLT has also observed 2024 YR₄ at multiple phase angles from 5° to 35°, which would allow for the construction of a phase curve which can constrain the asteroid's surface properties.^[10]

As an Apollo-type near-Earth object, 2024 YR₄ orbits the Sun on an elliptical orbit that crosses Earth's orbit.^[3] Since its close approach in December 2024, the asteroid has an orbital period of about 3.99 years and an orbital inclination of 3.41 degrees with respect to Earth's orbit (the ecliptic), but its orbit will be perturbed at the close encounter of 2032 if it does not impact Earth.^[3] Astronomers Carlos and Raúl de la Fuente Marcos have proposed that 2024 YR₄ could be related to a group of near-Earth asteroids on similar orbits that also have virtual impactors: 2017 UW₅, 2018 GG₄, 2019 SC, and 2020 MQ₆₁.^[19] The 2015 Porangaba meteor orbit has a 5% probability of matching that of 2024 YR₄.^[19]

The asteroid reached perihelion (its closest approach to the Sun) on 22 November 2024, and made a close approach to Earth on 25 December 2024, two days before its discovery. During this encounter, 2024 YR₄ passed 828,800 km (515,000 mi; 2.156 lunar distances) from Earth and then 488,300 km (303,400 mi; 1.270 LD) from the Moon.^[3] The asteroid will make its next close approach to Earth on 17 December 2028, when it will pass 8,010,000 ± 134,000 km (4,977,000 ± 83,000 mi; 20.84 ± 0.35 LD) from Earth.^[3] The 2028 encounter will provide astronomers the opportunity to perform additional observations and extend the observation arc by four years. This is expected to greatly improve calculations of 2024 YR₄'s orbit in preparation for its subsequent close approach on 22 December 2032.^[24] Since the 2032 close approach is not yet well constrained enough to rule out an Earth or Moon impact, the resulting perturbation by the Earth–Moon system is highly uncertain, and close approaches after 2032 are therefore not well constrained either. As of March 2025, the 3-sigma uncertainty in the asteroid's position will be ± 1300 km.^[25] By mid-2034, uncertainty in the position propagates to about 70 million km (43 million mi), or roughly half of the distance between Earth and the Sun.^[26] If 2024 YR₄ passes very close to Earth or the Moon in 2032, the uncertainty will be even greater due to its trajectory being affected by gravitational focusing. The possible trajectories become more divergent with time and result in a very small chance of an Earth impact in 2039.^[7]

• 
  Diagram of 2024 YR₄'s orbit
• 
  Animation of 2024 YR₄'s trajectory from 2028 to 2032, showing its 2032 close approach
  

  •   2024 YR₄
  •   Sun
  •   Mercury
  •   Venus
  •   Earth
  •   Mars

On 22 December 2032, the asteroid will come closest to Earth sometime between about 4:00 and 13:00 GMT,^[3][c] coming from the direction of Sagittarius.^[27] Calculations using the observation arc of 60 days as of 24 February 2025 find that 2024 YR₄ has a 1-in-59,000 (0.0017%) chance of impacting Earth on 22 December 2032 around 14:02 UT^[7] and a 1% possibility of impacting the Moon about an hour later around 15:19 UT. The nominal (best-fit) closest approach to Earth is on 22 December at 08:30 UT (with an uncertainty in the closest approach time of about 4 hours and being 6 hours earlier than virtual impactor) at a distance of 271,000 kilometres (168,000 miles; 0.70 lunar distances), with a 3-sigma uncertainty of 207,000 kilometres (129,000 miles; 0.538 lunar distances). The nominal closest approach to Moon is seven hours later at 15:05 UT (within 15 minutes of the lunar impact window) with a nominal distance of about 16,000 km (9,900 mi).^[3]

Due to 2024 YR₄'s size and previously greater-than-1% impact probability, it peaked at Torino scale rating level 3, which prompted the International Asteroid Warning Network to issue a notice on 29 January 2025.^[16][28] This was the second-highest Torino scale rating an asteroid has ever reached, behind 99942 Apophis which briefly ranked Torino scale level 4 in late 2004.^[28] NASA gave a Palermo scale rating as high as −0.18 for 2024 YR₄ on 18 February 2025 (when it had a 55 day observation arc),^[7] which corresponded to an impact hazard of 66% of the background hazard level. The asteroid never exceeded the background risk of a random asteroid of the same size impacting Earth by 2032, which would have corresponded to a Palermo scale rating of 0. On 23 February 2025 (with a 60 day observation arc), the asteroid was dropped to Torino scale Level 0, meaning the likelihood of a collision is effectively zero.

As of 23 February 2025 NASA gives Palermo scale rating of −3.45 for 2024 YR₄, which corresponds to an impact hazard of 0.08% of the background hazard level.^[7] NEODyS gives −4.38 with an impact probability of 0.000444%,^[29] while the European Space Agency gives a Palermo scale rating of −3.55 with an impact probability of 0.00162%.^[6]

The risk corridor of 2024 YR₄'s possible impact locations begins from the eastern equatorial Pacific Ocean, runs through northern South America, the equatorial Atlantic Ocean, Nigeria, central Africa, the north of eastern Africa, the southwest corner of the Arabian Peninsula, the northwestern Indian Ocean, India, and ends in Bangladesh.^[24][16] Using NASA's estimated diameter, mass, and density for 2024 YR₄, the asteroid would release energy equivalent to 7.8 megatonnes of TNT (32.6 PJ) if it were to impact Earth at its predicted velocity at atmospheric entry of 17.32 km/s (10.76 mi/s),^[7] equivalent to about 500 of the "Little Boy" bomb dropped on Hiroshima, two and a half of Grapple Y, 50% of Castle Bravo, or 15% of Tsar Bomba.^{[citation needed]} Due to its stony composition, this would more likely produce a meteor air burst than an impact crater (for an impact on a continent) or tsunami (for an oceanic impact). It could cause damage as far as 50 km (30 mi) from the impact site.^[21][28] Despite its potential to cause damage if it were to impact, 2024 YR₄ is not categorized as a potentially hazardous object (PHO) because it has an absolute magnitude dimmer than 22, which usually means that such an asteroid is less than 140 m (460 ft) in diameter and its potential damage therefore would be localized.^[30]

2024 YR₄ has a 1% chance of impacting the Moon on 22 December 2032^[31] around 15:17–15:21 UT.^[32] An impact before 15:18 would be visible in the shaded part of the 70% waning gibbous moon.^[32] The nominal approach to the moon is around 15:05 UT ± 4 hours at a distance of 16,000 km (9,900 mi; 0.042 LD).^[3]

The effects of the collision could create an impact crater 500 to 2,000 meters (0.3–1.2 miles) wide on the lunar surface, releasing about 5.2 megatonnes of TNT (21.8 PJ) of energy if it were to impact the Moon at a velocity estimated to be 13.9 km/s (8.7 mi/s), an explosion about 300 times more powerful than the Hiroshima bomb.^{[citation needed]} The potential impact zone extends from just south of Mare Crisium, a solidified lava plain, to Tycho, an ancient crater, all located on the visible side of the Moon.^[32]

Michael Busch of the SETI Institute, notes that an explosion on the Moon "would be very obvious to any spacecraft observing from lunar orbit" but may not be as visible to the unaided eye from Earth due to the Moon's brightness. However, other astronomers believe the impact could be visible from Earth. Gareth Collins suggested that "the impact flash of vaporized rock would be visible from Earth, even in the daytime", while Daniel Bamberger of the Northolt Branch Observatories in London stated that the impact "could be brighter than the full moon" making it clearly visible to the naked eye.^[34][35]

Additional observations of 2024 YR₄ are necessary to reduce uncertainties in its trajectory and determine whether it will impact Earth.^[16] Because the asteroid is now moving away from Earth, it is becoming fainter, necessitating the use of larger-aperture telescopes such as the 10-meter Keck telescope and the Very Large Telescope.^[17] The asteroid was not observed between 11–13 January and 8–15 February 2025^[1] due to interference from moonlight. After mid-February, a 2-meter telescope or better is required. After 4 March 2025, a 4-meter or better class telescope will be required. After 1 April, an 8-meter or better will be required. Space-based infrared telescopes such as the James Webb Space Telescope (JWST) will be able to observe 2024 YR₄ at farther distances until 20 May.^[36][17] The JWST is scheduled to observe 2024 YR₄ between 1 and 24 March, when the position of the asteroid first becomes compatible with the pointing restrictions of the telescope, and again between 20 April and 20 May 2025. JWST will use its NIRCam and Mid-Infrared Instrument, which will provide measurements of both 2024 YR₄'s position and its infrared thermal emission, from the latter of which the asteroid's size and albedo can be better estimated.^[37][18] NEOWISE entered Earth's atmosphere in November 2024,^[38] and therefore is not available to observe 2024 YR₄.

The orbital uncertainty of 2024 YR₄ may be further reduced with precovery observations, in which the asteroid would be detected in archival telescope images taken before its discovery. The earliest known precovery observation of 2024 YR₄ was by ATLAS on 25 December 2024, but this is just two days before its discovery and the measured position of the asteroid in that observation is also more uncertain than in later observations, due to the rapid motion of the asteroid and a longer exposure than would have been optimal for observations of such a fast-moving asteroid.^[39][n] The asteroid passed within 12 million km of Earth in September 2016 and within 20 million km of Earth in October 2020.^[3] A search through 2016 Subaru Telescope archival images did not find 2024 YR₄ in a region where it might have been.^[24]

Astronomers of the Catalina Sky Survey have inspected a set of images from Mount Lemmon Survey, including images containing the virtual impactor's predicted location; however, no candidates were found.^[36] Astronomers of the Pan-STARRS survey identified a few images in 2012, 2016 and 2020, again with no candidates found, alongside images from 2012 and 2020 which did not have a sufficiently deep limiting magnitude to detect 2024 YR4 at its predicted magnitude on those dates. Paolo Tanga checked for possible detections by the Gaia spacecraft, but concluded that 2024 YR₄ never came within the spacecraft's field of view. James Bauer checked the NEOWISE data, Deborah Woods checked Space Surveillance Telescope data, and Julien de Wit searched data from TESS and other exoplanet surveys; none of these searches found detections of 2024 YR₄.^[36]

A positive occultation detection would make possible measurements of the size and shape of the asteroid and more precise measurements of its position. As of 11 February 2025, no positive stellar occultation has been reported.^[41] A 6 February occultation had its path very close to the Connecticut–Rhode Island border, and no occultation results have been reported so far. An 8 February occultation passed Xiamen, China; Chenyang Guo reported negative results from two locations.^[42] The uncertainty range for the path of both occultations on Earth was a few kilometers wide, and while Fresnel diffraction broadens the penumbral to slightly more than twice the diameter of the asteroid—to 100 and 140 m (330 and 460 ft)—an uncertainty of a few kilometers is still too wide compared to this penumbra to efficiently place movable observing stations across the path.^[41]

Observations of the asteroid when it passes near Earth again in 2028 will enable the calculation of a very precise orbit and a much refined estimation of the impact likelihood in 2032 as it will extend the observation arc by four years. The asteroid will be too faint for observation until June 2028.^[16] It will be about magnitude 25 when it comes to opposition around 19 July 2028 at an Earth distance of 0.78 AU (117 million km) but it will continue to get closer until December 17 when it will be 20 LD (7.7 million km) away.^[3]

If the observations up to 2028 do not rule out a 2032 impact, then it might be possible to send an asteroid deflection mission similar to DART to 2024 YR₄ to avert its impact. However, it would be very challenging to mount such a mission with less than eight years to design and construct a spacecraft. A mission could be prepared before the 2028 close encounter so that it would be ready to launch if it is determined that an impact is likely. Alternatively, if deflection is unfeasible and the predicted site of impact is on or close to a continent, it could be evacuated.^[43]

• Asteroid impact avoidance
• 99942 Apophis

• 2024 YR4 at NeoDyS-2, Near Earth Objects—Dynamic Site
  • Ephemerides · Observation prediction · Orbital info · MOID · Proper elements · Observational info · Close approaches · Physical info · Orbit animation
• 2024 YR4 at ESA–space situational awareness
  • Ephemerides · Observations · Orbit · Physical properties · Summary
• 2024 YR4 at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit viewer · Orbit parameters · Physical parameters
• 2024 YR4 Overview, NASA, 7 February 2025
• Close approach fact sheet for asteroid 2024 YR4, ESA's NEO Coordination Centre
• Images of 2024 YR4, taken by ATLAS in January 2025, at b612.ai
• Asteroidticker, comparative JPL data on NEOs in imperial units
• Light curve of 2024 YR₄ by Petr Pravec, Ondrejov Asteroid Photometry Project