 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) | |
| Epoch 5 May 2025 (JD 2460800.5) | |
| Uncertainty parameter 4 | |
| Observation arc | 71 days |
| Earliestprecovery date | 25 December 2024 |
| Aphelion | 4.180 AU |
| Perihelion | 0.8515 AU |
| 2.5159 AU | |
| Eccentricity | 0.6616 |
| 3.991yr (1457.62 days) | |
| 40.40° | |
| 0.2470° per day | |
| Inclination | 3.408° |
| 271.366° | |
| 134.361° | |
| Earth MOID | 0.00283 AU (423,000 km; 1.10 LD) |
| Jupiter MOID | 1.2715 AU |
| Physical characteristics | |
| 0.32440 ± 0.00002 h (19.4640 ± 0.0012 min)[10] | |
| ~ −25°[6] | |
| ~ 42°[6] | |
2024 YR4 is anasteroid with an estimated diameter of 40 to 90 metres (130 to 300 ft) 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, with 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, but later predictions generated from additional observations produced a negligible chance of an Earth impact in 2032 and reduced the asteroid's Torino rating to 0. It retains a small chance of impacting the Moon in 2032.
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 indicated an impact probability of greater than 1%, the first step inplanetary defense responses was triggered, prompting additional data gathering using several major telescopes and leadingUnited 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 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.[9] A number of known asteroids, including othervirtual impactors,[a] 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] The first letter, "Y", 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]
The diameter of2024 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).[8][19] If2024 YR4 reflects between 5% and 25% of visible light, as do the vast majority of asteroids with a measured albedo, then its diameter is between 40 and 90 m (130 and 300 ft).[7] An estimate byNASA places its diameter at 55 m (180 ft) for an assumed geometric albedo of 0.154.[8] These estimates make2024 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.[19]2024 YR4 is significantly smaller thanDimorphos, the impact target of NASA'sDouble Asteroid Redirection Test (DART) in 2022. The diameter and albedo of2024 YR4 could be further constrained withthermal infrared observations,radar observations, anoccultation of a star, or direct imaging by a spacecraft.[20]
The mass and density of2024 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),[21] which is within the density range for stony asteroids such as243 Ida,[22] with an assumed diameter of 55 m (180 ft), theSentry risk table estimates a mass of 2.2×108 kg (4.9×108 lb).[8] 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.
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.[11][9][b] Spectroscopy by theGemini South telescope in February 2025 suggest either anR or Sa spectral type for2024 YR4.[6]
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.[11][10] Observations by the Gemini South telescope from February 2025 found similar results for2024 YR4's rotation period.[6] This is a relatively fast rotation period for an asteroid, although it is not fast enough to rule out arubble pile structure for2024 YR4.[9] 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.[11]
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.[10][9] 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 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 by 2031.[23] Its orbit will be stronglyperturbed at the close encounter of 2032. 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 meteor 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.[6] 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.[6] 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.[6]
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 ± 107,000 km (4,977,000 ± 66,000 mi; 20.84 ± 0.28 LD) from Earth.[3] The 2028 encounter will provide astronomers the opportunity to perform additional observations and extend theobservation arc by four years. This is expected to greatly improve calculations of2024 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,[update] the3-sigma uncertainty in the asteroid's position is± 1000 km.[25] By mid-2034, uncertainty in the position propagates to about 300 million km (190 million mi), twice the distance between Earth and the Sun.[26] If2024 YR4 passes very close to Earth or the Moon in 2032, the uncertainty will be even greater due to its trajectory being affected bygravitational focusing. The possible trajectories become more divergent with time and the greatest risk of an Earth impact is in December 2047.[c][8]
![Animation of 2024 YR4's trajectory from 2028 to 2036 (with 2036 being highly uncertain)[d] 2024 YR4 Sun Mercury Venus Earth Mars](/mt/?noimg=&dark=on&url=http%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 05:30 and 12:00 UTC,[3][e][f] approaching from the direction ofSagittarius.[27] Calculations using anobservation arc of 71 days, from 25 December 2024 to 6 March 2025, give2024 YR4 a 1-in-5.3-million (0.000019%) chance ofimpacting Earth on 22 December 2032.[8] The nominal (best-fit) closest approach to Earth on 22 December 2032 is at 08:42 UTC (with an uncertainty of about 3.2 hours in the closest-approach time), at a distance of 262,000 km (163,000 mi), with a3-sigma uncertainty of 154,000 km (96,000 mi). The nominal closest approach to the Moon occurs at 15:15 UTC, with a nominal distance of about 6,000 km (3,700 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][28] This was the second-highest Torino rating ever reached by an asteroid, behind99942 Apophis, which briefly reached a rating of 4 in late 2004.[28] 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.[8] 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).[g] The asteroid never exceeded the background risk of a random asteroid of the same size impacting Earth by 2032, which 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.[29] On 23 February 2025 (with a 60-day observation arc),2024 YR4 was reduced to a Torino rating of 0.
As of 18 March 2025,[update] NASA gives2024 YR4 a Palermo rating of−5.38 and rules out a 2032 impact with 5-sigma confidence.[8] The European Space Agency removed the chance of a 2032 impact on 8 March 2025.[7]NEODyS removed the chance of a 2032 impact on 1 March 2025.[30]
| JPL Horizons nominal geocentric distance (AU) | uncertainty region (3-sigma) |
|---|---|
| 0.0024 AU (360,000 km; 0.93 LD)[31] | ± 220 thousand km[31][h][i] |
Evolution of nominal Earth close-approach estimates for 22 December 2032 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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A risk corridor of2024 YR4's possible impact locations in 2032, estimated from existing observations in late January 2025, 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 for2024 YR4, the asteroid would release energy equivalent to 7.7megatonnes of TNT (32.2 petajoules) if it were to impact Earth at its predicted velocity at atmospheric entry of 17.20 km/s (10.69 mi/s),[8] 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 more likely produce ameteor air burst than animpact crater (for an impact on land) ortsunami (for an oceanic impact). It could cause damage as far as 50 km (30 mi) from the impact site.[19][28] 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.[32]
2024 YR4 has around a 1.7% chance (1-in-58) of impacting a 70%waning gibbous moon on 22 December 2032[33] around 15:17 to 15:21 UTC.[34] The nominal approach to the Moon is near the impact scenario at around 15:15 UTC ± 3 hours at a distance of 6,000 km (3,700 mi; 0.016 LD),[3] with a3-sigma uncertainty of 162,000 km (101,000 mi).[35] The Moon has a radius of 1,737 km.
| JPL Horizons nominal lunar distance (AU) | uncertainty region (3-sigma) |
|---|---|
| 0.00005 AU (7,500 km; 0.019 LD)[36] | ± 214 thousand km[36] |
The impact could create an impact crater with a diameter of 500 to 2,000 metres (0.31 to 1.24 mi) wide on the lunar surface, releasing about 5.2 megatonnes of TNT (21.8 petajoules) of 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.[37] The impact corridor is a line that extends through the southern parts ofMare Humorum andMare Nubium.[34][dubious –discuss]
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" making it clearly visible to the naked eye.[38][39]
Evolution of nominal lunar close approach estimates for 2032 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Additional observations of2024 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-meterKeck telescope and theVery Large Telescope.[20] 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 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-basedinfrared telescopes such as theJames Webb Space Telescope (JWST) will be able to observe2024 YR4 at farther distances until 20 May.[40][20] The JWST is scheduled to observe2024 YR4 8 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 itsNIRCam andMid-Infrared Instrument, which will provide measurements of both2024 YR4's position and its infraredthermal emission, from the latter of which the asteroid's size and albedo can be better estimated.[41][42]NEOWISE burned up in Earth's atmosphere in November 2024,[43] and therefore is not available to observe2024 YR4.
The orbital uncertainty of2024 YR4 may be further reduced withprecovery 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 also 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.[44][v] 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 a region where it might have been.[24]
Astronomers of theCatalina Sky Survey have inspected a set of images fromMount Lemmon Survey, including images containing the virtual impactor's predicted location; however, no candidates were found.[40] 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.[40]
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 has been reported.[46] 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.[47] The uncertainty range for the path of both occultations on Earth was a few kilometers wide, and whileFresnel diffraction broadens thepenumbral 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.[46]
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 toopposition 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 20.83 LD (8.01 million km) away.[3]
Had the observations up to 2028 not ruled out a 2032 Earth impact with a 5-sigma confidence,[8] then it might have been useful to send anasteroid deflection mission similar toDART to2024 YR4 to avert its impact. However, mounting such a mission with less than eight years to design and construct a spacecraft would be 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 is unfeasible and the predicted site of impact is on or close to a continent, it could beevacuated.[48]
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.
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