 2024 YR4 (centered) tracked by theVery Large Telescope in January 2025 | |
| Discovery[1][2] | |
|---|---|
| Discovered by | ATLAS–CHL (W68) |
| Discovery site | Río Hurtado, Chile |
| Discovery date | 27 December 2024 |
| Designations | |
| 2024 YR4 | |
| Orbital characteristics[3] (JPL #78) | |
| Epoch 21 Nov 2025 (JD 2461000.5) | |
| Uncertainty parameter 3 | |
| Observation arc | 137 days |
| Earliestprecovery date | 25 December 2024 |
| Aphelion | 4.180 AU[a] |
| Perihelion | |
| 2.5158 AU | |
| Eccentricity | 0.6615 |
| 3.991yr (1457.57 days) | |
| 40.40° | |
| 0.2470° per day | |
| Inclination | 3.4082° |
| 271.364° | |
| 134.366° | |
| Earth MOID | 0.002803 AU (419,300 km; 1.091 LD) |
| Jupiter MOID | 1.2711 AU |
| Physical characteristics | |
| 60±7 m[7] | |
| 0.32440 ± 0.00002 h (19.4640 ± 0.0012 min)[8] | |
| ~ 42°[9] | |
| ~ −25°[9] | |
| 0.13±0.05[7] | |
2024 YR4 is anasteroid with an estimated diameter of 53 to 67 metres (174 to 220 ft)[7] that is classified as anApollo-type (Earth-crossing)near-Earth object. From 27 January to 20 February 2025, it had an impact rating of 3 on theTorino scale, reflecting its size and an estimated probability greater than 1% that it wouldimpact Earth on 22 December 2032. The estimated impact probability peaked at 3.1% on 18 February 2025. By 23 February, additional observations effectively ruled out2024 YR4 impacting Earth in 2032 and lowered its Torino rating to 0. Based on all observations up to aJames Webb Space Telescope observation on 11 May 2025, there is a roughly 4% chance of impacting the Moon on 22 December 2032 around 15:19UTC, with the asteroid expected to pass at9000±74000 km from the surface of the Moon.
The asteroid was discovered by the Chilean station of theAsteroid Terrestrial-impact Last Alert System (ATLAS) atRío Hurtado on 27 December 2024.[1][2] When additional observations increased its impact probability to greater than 1%, the first step inplanetary defense responses was triggered, prompting additional data gathering using several major telescopes and leading 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 it will be moving away from the Sun until November 2026. Its next close approach will take place on 17 December 2028.[3] Analysis of spectral andphotometric time series suggests that2024 YR4 is a stonyS-type (most likely),L-type orK-type asteroid, with arotation period of approximately 19.5 minutes.[11] A number of known asteroids, including othervirtual impactors,[c] follow orbits somewhat consistent with that of2024 YR4.[17]
The asteroid'sprovisional designation as aminor planet, "2024 YR4", was assigned by theMinor Planet Center when its discovery was announced on 27 December 2024.[2] "Y", the first letter after the discovery year, indicates that the asteroid was discovered in the second half-month of December (16 to 31 December), and "R4" indicates that it was the 117th provisional designation to be assigned in that half-month.[18]
Measurements of2024 YR4'smid-infraredthermal emission by theJames Webb Space Telescope (JWST) on 26 March 2025 indicate that it has a diameter of 60 m (200 ft), with an uncertainty of 7 m (23 ft).[19] This makes2024 YR4 around the same size as the asteroid that caused the 1908Tunguska event or theiron–nickel asteroid that created theMeteor Crater inArizona 50,000 years ago.[20]2024 YR4 is significantly smaller thanDimorphos, the impact target of NASA'sDouble Asteroid Redirection Test (DART) in 2022. The possible size range implies ageometric albedo between 0.08 and 0.18, relatively low for a stony asteroid.[7]
Prior to this measurement, more uncertain estimates for2024 YR4's diameter were based on its brightness (absolute magnitude) and using a range of plausible values for its surface reflectivity (geometric albedo).[21][20] If2024 YR4 reflects between 5% and 25% of visible light, as do the vast majority of asteroids with a measured albedo, then its diameter had to be between 40 and 90 m (130 and 300 ft).[22] An estimate byNASA for instance placed its diameter at 55 m (180 ft) by assuming a geometric albedo of 0.154.[21]
The mass and density of2024 YR4 have not been measured, but the mass can be loosely estimated with an assumed density and the estimated diameter. Assuming a density of 2.6 g/cm3 (1.5 oz/cu in),[23] which is within the density range for stony asteroids such as243 Ida,[24] and the then nominal diameter of 55 m (180 ft), theSentry risk table estimated a mass of 2.2×108 kg (4.9×108 lb).[21] Rescaling the diameter to the now better measured value of 60 m (200 ft) increases the estimated mass to 2.8×108 kg (6.2×108 lb). Both the assumed density and the inferred diameter contribute large uncertainties to the mass estimated.
Preliminaryspectroscopic analysis from theGran Telescopio Canarias andLowell Discovery Telescope suggests that2024 YR4 is either anS-type asteroid (17% of the asteroid population), anL-type asteroid, or aK-type asteroid, all of which point to astony composition.[10][11][d] Spectro-photometry by theGemini South telescope in February 2025 suggest either anR or Sa spectral type for2024 YR4.[9] JWST measurements of2024 YR4's thermal emission suggest "a rockier surface than commonly inferred."[7]
Photometric observations by theVery Large Telescope (VLT) and theLa Silla Observatory's 1.54-metre (5.1 ft) telescope indicate2024 YR4 has arotation period near 19.5 minutes.[10][8] Observations by the Gemini South telescope from February 2025 found similar results for2024 YR4's rotation period.[9] This is a relatively fast rotation period for an asteroid, although it is not fast enough to rule out arubble pile structure for2024 YR4.[11] The VLT has also observed2024 YR4 at multiplephase angles from 5° to 35°, which would allow for the construction of aphase curve which can constrain the asteroid's surface properties.[10]
The brightness of2024 YR4 varies by 0.42magnitudes 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.[8][11] Gemini South telescope measurements of2024 YR4's rotationallight curve at variousphase angles show that the asteroid has aretrograde rotation and a highly flattened shape with an equatorial diameter roughly 3 times as long as its polar diameter.
As anApollo-typenear-Earth object,2024 YR4 orbits the Sun on anelliptical orbit that crossesEarth's orbit.[3] Since its close approach in December 2024, the asteroid has anorbital period of about 3.99 years (1,458 d) and anorbital inclination of 3.41 degrees with respect to Earth's orbit (theecliptic).[3] The period, considered as anosculating element, dips slightly at the approach in December 2028 and then slowly rises to around 4.01 years (1,463 d) by 2031.[25] Its orbit will be stronglyperturbed at the close encounter of 2032 (if it doesn't hit the moon). Astronomers Carlos and Raúl de la Fuente Marcos have proposed that2024 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, and2020 MQ61.[17] The 2015 Porangaba meteorite orbit has a 5% probability of matching that of2024 YR4.[17]
Due to theYarkovsky effect,2024 YR4's retrograde rotation causes its orbit to shrink over time.[9] This indicates2024 YR4 originated farther out in the Solar System, specifically the centralmain asteroid belt.2024 YR4's stony composition supports the possibility of an origin from the central main belt, since S-type and C-type asteroids are the most abundant spectral types in that region.[9] The inward migration of2024 YR4 from the main belt to near-Earth space was likely chaotic since the asteroid would have to cross multipleorbital resonances, such as the 3:1 mean-motion resonance withJupiter's orbital period at 2.5 AU and the ν6secular resonance withSaturn's orbital precession at 2.2 AU.[9]
The asteroid reachedperihelion (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; 2.156lunar 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 ± 60,000 km (4,977,000 ± 37,000 mi; 20.84 ± 0.16 LD) from Earth.[3] The 2028 encounter will provide astronomers the opportunity to perform additional observations and extend theobservation arc by four years. This will significantly improve calculations of2024 YR4's orbit in preparation for its subsequent close approach on 22 December 2032.[26]
Since the 2032 close approach is not yet well constrained enough to rule out a Moon impact, the resulting perturbation by the Earth–Moon system is highly uncertain, and all close approaches after 2032 are therefore not well constrained either. The 1 March 2025 position of the asteroid is known with a3-sigma uncertainty in the asteroid's position of±500 km.[27] By mid-2034, this increases to about 50 million km (31 million mi), or about 1/3 the distance between Earth and the Sun,[28] but since2024 YR4 is expected to pass very close to the Moon in 2032, the post-2032 uncertainty will be even greater due to its trajectory being affected (seegravitational focusing).[29] The possible trajectories become more divergent with time and the greatest risk of an Earth impact is in December 2047.[21][30] By December 2047, the uncertainty in the asteroid's position along its orbit is at least 2 billion km (13 AU) and wraps around the asteroid's orbit.[31][e][f]
![Animation of 2024 YR4's trajectory from 2028 to 2036 (with 2036 being highly uncertain)[b] 2024 YR4 Sun Mercury Venus Earth Mars](/mt/?noimg=&dark=on&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aAnimation_of_2024_YR4_around_Sun_-_2032_close_approach.gif)
On 22 December 2032,2024 YR4 will come closest to Earth sometime between 07:00 and 10:30 UTC,[3][g][h] approaching from the direction ofSagittarius.[32] The nominal (best-fit) closest approach to Earth on 22 December 2032 is at 08:36 UTC (with an uncertainty of about 1.5 hours in the closest-approach time), at a distance of 270,000 km (170,000 mi), with a3-sigma uncertainty of 69,000 km (43,000 mi). The nominal closest approach to the Moon occurs at 15:10 UTC, with a nominal distance of about 11,000 km (6,800 mi).[3]
Due to2024 YR4's size and previously greater-than-1% impact probability, it reached a rating of 3 on theTorino scale on 27 January 2025, which prompted theInternational Asteroid Warning Network to issue a notice on 29 January 2025.[16][33] This was the second-highest Torino rating ever reached by an asteroid, behind the larger99942 Apophis which briefly reached a rating of 4 in late 2004.[33] NASA's Sentry gave2024 YR4 a rating on thePalermo scale as high as−0.18 on 18 February 2025, when it had a 55-day observation arc and a 3.1% chance of impacting the Earth in 2032.[21] This gave2024 YR4 a corresponding impact hazard of 66% of the background hazard level, given the asteroid's relatively small size of 60 metres (200 ft).[i] The asteroid approached but never exceeded the background risk of a random asteroid of the same size impacting Earth by 2032, which by definition corresponds to a Palermo rating of 0. On 18 February 2025, theEuropean Space Agency's Aegis listed a 2.8% chance of an Earth impact in 2032.[34] On 23 February 2025 (with a 60-day observation arc),2024 YR4 was reduced to a Torino rating of 0.
On 2 April 2025, with a 91-day observation arc, NASA removed the chance of a 2032 Earth impact.[21] The European Space Agency removed the chance of a 2032 impact on 8 March 2025.[22]NEODyS removed the chance of a 2032 impact on 1 March 2025.[30]
| JPL Horizons nominal geocentric distance (AU) | uncertainty region (3-sigma) |
|---|---|
| 0.0025 AU (370,000 km; 0.97 LD)[35] | ± 97 thousand km[35][j][k] |
Evolution of nominal Earth close-approach estimates for 22 December 2032 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
As of late January 2025, the risk corridor of2024 YR4's possible impact locations in 2032, estimated from the existing observations, began from the eastern equatorial Pacific Ocean, ran 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 ended in Bangladesh.[26][16] Using NASA's estimated diameter, mass, and density for2024 YR4, the asteroid would have released energy equivalent to 7.7megatonnes of TNT (32.2 petajoules) if it had been to impact Earth at its predicted velocity at atmospheric entry of 17.20 km/s (10.69 mi/s),[21] equivalent to about 500 times the energy released byLittle Boy (theatomic bomb dropped on Hiroshima), two and a half times ofGrapple Y, 50% ofCastle Bravo, or 15% ofTsar Bomba.[citation needed]
Due to its stony composition, this would have more likely produced ameteor air burst than animpact crater (for an impact on land) ortsunami (for an oceanic impact). It could have caused damage as far as 50 km (30 mi) from the impact site.[20][33] Despite its potential to cause damage if it were to impact,2024 YR4 is not categorized as apotentially hazardous object (PHO) because it has anabsolute 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.[36]
.png)
Using observations through 11 May 2025,2024 YR4 has around a 4% chance of impacting a 70%waning gibbous moon on 22 December 2032[37] around 15:17 to 15:21 UTC.[38] Observations by theJames Webb Space Telescope on 11 May 2025 reduced the Earth approach uncertainty region by 20%[v] and increased the odds of a Moon impact from 3.8% to 4.3%.[37] The nominal approach to the Moon is near the impact scenario at around 15:10 UTC ± 1.3 hours at a distance of 10,700 km (6,600 mi; 0.028 LD) from the center of the Moon, or about 9,000 km above the 1,737 km radius of the Moon,[3] with a3-sigma uncertainty of 74,000 km (46,000 mi).[39]
| JPL Horizons nominal lunar distance (AU) | uncertainty region (3-sigma) |
|---|---|
| 0.000091 AU (13,600 km; 0.035 LD)[40] | ± 97 thousand km[40] |
The impact could create a crater with a diameter of 500 to 2,000 metres (0.31 to 1.24 mi) on the lunar surface, releasing the equivalent of 5.2 megatonnes of TNT (21.8 petajoules) in energy if it were to impact the Moon at an estimated velocity of 13.9 km/s (8.6 mi/s), an explosion about 340 times more powerful than the Hiroshima bomb.[41] The impact corridor is a line that extends through the southern parts ofMare Humorum andMare Nubium.[38][dubious –discuss] It is estimated that such an impact would send approximately 100,000 tons of debris into space. This cloud of debris could result in an extraordinary meteor shower and also pose a hazard for artificial Earth satellites.[42]
Michael Busch of theSETI 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 theNortholt Branch Observatories in London stated that the impact "could be brighter than the full moon"[dubious –discuss] making it clearly visible to the naked eye.[43][44]
Evolution of nominal lunar close approach estimates for 2032 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Additional observations of2024 YR4 reduced the uncertainties in its trajectory.[16] Because the asteroid was already moving away from Earth when it was discovered, it was becoming fainter, necessitating the use of larger-aperture telescopes such as the 10-meterKeck telescope and theVery Large Telescope.[45] As of 14 March 2025 the asteroid had reachedapparent magnitude 26,[12] which is 63 million times fainter than what can be observed with thenaked eye.[z] As of the last ground−based observation on 23 March 2025 byParanal Observatory, the asteroid was 1.8 AU from the Sun which is just beyond the orbit ofMars.[46] The asteroid was not observed between 11–13 January and 8–15 February 2025[1] due to interference from moonlight. After mid-February, a2-meter telescope or better was required. After 4 March 2025, a 4-meter or better class telescope became required. After 1 April, an 8-meter or larger was required. Space-basedinfrared telescopes like the JWST were able to observe2024 YR4 at farther distances until mid-May.[47][45] The JWST observed2024 YR4 on 8 March, when the position of the asteroid first became compatible with the pointing restrictions of the telescope, then 26 March, and observed it a final time on 11 May 2025, those observations likely being the last of the asteroid before its upcoming 2028 approach.[48] JWST has used itsNIRCam andMid-Infrared Instrument to measure2024 YR4's position, infrared thermal emission, and size.[7]
The orbital uncertainty of2024 YR4 would be further reduced byprecovery observations, in which the asteroid would be detected in archival telescope images taken before its discovery. The earliest known precovery observation of2024 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 more uncertain than in later observations, due to the rapid motion of the asteroid and a longerexposure than would have been optimal for observations of such a fast-moving asteroid.[49][aa] 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 2016Subaru Telescope archival images did not find2024 YR4 in part of the sky region where it should have been.[26]
Astronomers of theCatalina Sky Survey inspected a set of images fromMount Lemmon Survey, including images containing the virtual impactor's predicted location, and similarly found no candidates.[47] Astronomers of thePan-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 deeplimiting magnitude to detect 2024 YR4 at its predicted magnitude on those dates. Paolo Tanga checked for possible detections by theGaia spacecraft, but concluded that2024 YR4 never came within the spacecraft's field of view. James Bauer checked theNEOWISE data, Deborah Woods checkedSpace Surveillance Telescope data, and Julien de Wit searched data fromTESS and other exoplanet surveys; none of these searches found detections of2024 YR4.[47]
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,[update] no positivestellar occultation had been reported.[51] A 6 February occultation had its path very close to theConnecticut–Rhode Island border, and no occultation results have been reported so far. An 8 February occultation passedXiamen, China; Chenyang Guo reported negative results from two locations.[52] The uncertainty range for the path of both occultations on Earth was a few kilometers wide, and whileFresnel diffraction broadens thepenumbra 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.[51]
Observations of the asteroid when it passes near Earth again in 2028 will extend the observation arc by four years. This will enable the calculation of a very precise orbit and a much refined estimation of the Moon impact likelihood in 2032.[16] The asteroid will be too faint for observation until June 2028. It will be about magnitude 25 when it comes toopposition on 19 July 2028 at an Earth distance of 0.78 AU (117 million km)[53] and it will continue to get closer until 17 December when it will pass about 20.8 LD (8.0 million km; 5.0 million mi) from Earth.[3]
Had the observations not ruled out a 2032 Earth impact with a 5-sigma confidence,[21] anasteroid deflection mission similar toDART might have been sent to2024 YR4 to avert its impact. However, mounting such a mission with less than eight years to design and construct a spacecraft would have been challenging. 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 were unfeasible and the predicted site of impact were on or close to a continent, it could beevacuated.[54]
mass: This estimate assumes a uniform spherical body with the computed diameter and a mass density of 2.6 g/cm3. The mass estimate is somewhat more rough than the diameter estimate, but generally will be accurate to within a factor of three.
2024 in space | |||
|---|---|---|---|
Space probe launches |
|  | |
| Impact events | |||
| SelectedNEOs | |||
| Discoveries |
| ||
| Comets | |||
2025 in space | |||
|---|---|---|---|
| Space probe launches |
|    | |
| SelectedNEOs | |||
| Discoveries |
| ||
| Comets | |||
| Novae | |||
| Space exploration | Lucy flyby of52246 Donaldjohanson | ||
| Miscellaneous events |
| ||
