# 2024 YR4

2024 YR$_4$ is an asteroid with an estimated diameter of 40 to 90 metres (130 to 300 ft) that is classified as an Apollo-type (Earth-crossing) near-Earth object. From 27 January to 20 February 2025, it had an impact rating of 3 on the Torino scale, with an estimated probability greater than 1% that it would impact 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 the Asteroid Terrestrial-impact Last Alert System (ATLAS) at Río Hurtado on 27 December 2024. When additional observations indicated an impact probability of greater than 1%, the first step in planetary defense responses was triggered, prompting additional data gathering using several major telescopes and leading United Nations–endorsed space agencies to begin planning asteroid threat mitigation.
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. Analysis of spectral and photometric time series suggests that 2024 YR$_4$ is a stony S-type (most likely), L-type or K-type asteroid, with a rotation period of approximately 19.5 minutes. A number of known asteroids, including other virtual impactors, follow orbits somewhat consistent with that of 2024 YR$_4$.

## Provisional designation

The asteroid's provisional designation as a minor planet, "2024 YR$_4$", was assigned by the Minor Planet Center when its discovery was announced on 27 December 2024. The first letter, "Y", indicates that the asteroid was discovered in the second half-month of December (16 to 31 December), and "R$_4$" indicates that it was the 117th provisional designation to be assigned in that half-month.

## Physical characteristics
### Size and mass

The diameter of 2024 YR$_4$ 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). If 2024 YR$_4$ 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). An estimate by NASA places its diameter at 55 m (180 ft) for an assumed geometric albedo of 0.154. These estimates make 2024 YR$_4$ 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. 2024 YR$_4$ is significantly smaller than Dimorphos, the impact target of NASA's Double Asteroid Redirection Test (DART) in 2022. The diameter and albedo of 2024 YR$_4$ could be further constrained with thermal infrared observations, radar observations, an occultation of a star, or direct imaging by a spacecraft.
The mass and density of 2024 YR$_4$ 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/cm$^3$ (1.5 oz/cu in), which is within the density range for stony asteroids such as 243 Ida, with an assumed diameter of 55 m (180 ft), the Sentry risk table estimates a mass of 2.2×10$^8$ kg (4.9×10$^8$ lb). 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.

### Composition, rotation, and shape

Preliminary spectroscopic analysis from the Gran Telescopio Canarias and Lowell Discovery Telescope suggests that 2024 YR$_4$ 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. Spectroscopy by the Gemini South telescope in February 2025 suggest either an R or Sa spectral type for 2024 YR$_4$.
Photometric observations by the Very Large Telescope (VLT) and the La Silla Observatory's 1.54-metre (5.1 ft) telescope indicate 2024 YR$_4$ has a rotation period near 19.5 minutes. Observations by the Gemini South telescope from February 2025 found similar results for 2024 YR$_4$'s rotation period. 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 YR$_4$. The VLT has also observed 2024 YR$_4$ 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.
The brightness of 2024 YR$_4$ 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. Gemini South telescope measurements of 2024 YR$_4$'s rotational light curve at various phase angles show that the asteroid has a retrograde rotation and a highly flattened shape with an equatorial diameter roughly 3 times as long as its polar diameter.

## Orbit

As an Apollo-type near-Earth object, 2024 YR$_4$ orbits the Sun on an elliptical orbit that crosses Earth's orbit. 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). The period, considered as an osculating element, dips slightly at the approach in December 2028 and then slowly rises to around 4.01 years by 2031. Its orbit will be strongly perturbed at the close encounter of 2032. Astronomers Carlos and Raúl de la Fuente Marcos have proposed that 2024 YR$_4$ could be related to a group of near-Earth asteroids on similar orbits that also have virtual impactors: 2017 UW$_5$, 2018 GG$_4$, 2019 SC, and 2020 MQ$_{61}$. The 2015 Porangaba meteor orbit has a 5% probability of matching that of 2024 YR$_4$.
Due to the Yarkovsky effect, 2024 YR$_4$'s retrograde rotation causes its orbit to shrink over time. This indicates 2024 YR$_4$ originated farther out in the Solar System, specifically the central main asteroid belt. 2024 YR$_4$'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. The inward migration of 2024 YR$_4$ from the main belt to near-Earth space was likely chaotic since the asteroid would have to cross multiple orbital resonances, such as the 3:1 mean-motion resonance with Jupiter's orbital period at 2.5 AU and the ν$_6$ secular resonance with Saturn's orbital precession at 2.2 AU.
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 YR$_4$ 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. 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. 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 YR$_4$'s orbit in preparation for its subsequent close approach on 22 December 2032. 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 is ± 1000 km. By mid-2034, uncertainty in the position propagates to about 300 million km (190 million mi), twice the distance between Earth and the Sun. If 2024 YR$_4$ 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 the greatest risk of an Earth impact is in December 2047.
* Diagram of 2024 YR$_4$'s orbit
* Animation of 2024 YR$_4$'s trajectory from 2028 to 2036 (with 2036 being highly uncertain) 2024 YR$_4$ Sun Mercury Venus Earth Mars
* Animation of 2024 YR$_4$ around the Earth showing its 2032 close approach 2024 YR4 · Moon · Earth ·

## 2032 close approach

On 22 December 2032, 2024 YR$_4$ will come closest to Earth sometime between 05:30 and 12:00 UTC, approaching from the direction of Sagittarius. Calculations using an observation arc of 71 days, from 25 December 2024 to 6 March 2025, give 2024 YR$_4$ a 1-in-5-million (0.00002%) chance of impacting Earth on 22 December 2032. 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 a 3-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).
Due to 2024 YR$_4$'s size and previously greater-than-1% impact probability, it reached a rating of 3 on the Torino scale on 27 January 2025, which prompted the International Asteroid Warning Network to issue a notice on 29 January 2025. This was the second-highest Torino rating ever reached by an asteroid, behind 99942 Apophis, which briefly reached a rating of 4 in late 2004. NASA's Sentry gave 2024 YR$_4$ a rating on the Palermo 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. This gave 2024 YR$_4$ a corresponding impact hazard of 66% of the background hazard level, given the asteroid's relatively small size of 60 metres (200 ft). 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, the European Space Agency's Aegis listed a 2.8% chance of an Earth impact in 2032. On 23 February 2025 (with a 60-day observation arc), 2024 YR$_4$ was reduced to a Torino rating of 0.
As of 13 March 2025, NASA gives 2024 YR$_4$ a Palermo rating of −5.37 and rules out a 2032 impact with 5-sigma confidence. The European Space Agency removed the chance of a 2032 impact on 8 March 2025. NEODyS removed the chance of a 2032 impact on 1 March 2025.
JPL #74 nominal distance for the 22 December 2032 14:02 UT Virtual Impactor Scenario :
| JPL Horizons nominal geocentric distance (AU) | uncertainty region (3-sigma) |
| 0.0024 AU (360,000 km; 0.93 LD) | ± 220 thousand km |
Evolution of nominal Earth close-approach estimates for 22 December 2032 :
| Solution | Observation arc (in days) | JPL Horizons nominal geocentric distance (AU) | uncertainty region (3-sigma) | Impact probability | Torino scale | Palermo scale (max) |
| 2024 Dec 30 | 2 (53 obs) | | | 1:1040 (0.096%) | 1 | −1.73 |
| 2024 Dec 31 | 3 (71 obs) | | | 1:920 (0.11%) | 1 | −1.66 |
| 2025 Jan 1 | 4 (87 obs) | | | 1:870 (0.11%) | 1 | −1.64 |
| 2025 Jan 2 | 6 (109 obs) | | | 1:842 (0.12%) | 1 | −1.63 |
| 2025 Jan 3 | 7 (120 obs) | | | 1:760 (0.13%) | 1 | −1.61 |
| JPL #14 2025 Jan 6 | 8 (145 obs) | 0.01706 AU (2.552 million km; 6.64 LD) | ± 9.62 million km | 1:730 (0.14%) | 1 | |
| JPL #15 2025 Jan 6 | 11 (158 obs) | 0.01537 AU (2.299 million km; 5.98 LD) | ± 9.55 million km | 1:710 (0.14%) | 1 | −1.53 |
| 2025 Jan 11 | 14 (170 obs) | | | 1:630 (0.16%) | 1 | −1.53 |
| JPL #27 2025 Jan 20 | 26 (198 obs) | | | 1:320 (0.31%) | 1 | |
| JPL #30 2025 Jan 22 | 28 (213 obs) | 0.00068 AU (102,000 km; 0.26 LD) | ± 3.37 million km | 1:190 (0.52%) | 1 | −0.93 |
| JPL #32 2025 Jan 23 | 29 (219 obs) | 0.00171 AU (256,000 km; 0.67 LD) | ± 2.28 million km | 1:110 (0.91%) | 1 | −0.69 |
| JPL #34 2025 Jan 24 | 30 (227 obs) | 0.00113 AU (169,000 km; 0.44 LD) | ± 1.96 million km | 1:110 (0.91%) | 1 | −0.69 |
| JPL #35 2025 Jan 27 | 33 (238 obs) | 0.00004564 AU (6,829 km; 0.01776 LD) | ± 1.605 million km | 1:83 (1.2%) | 3 | −0.57 |
| JPL #36 2025 Jan 28 | 34 (245 obs) | 0.00071 AU (106,000 km; 0.28 LD) | ± 1.55 million km | 1:83 (1.2%) | 3 | −0.56 |
| JPL #37 2025 Jan 29 | 35 (257 obs) | 0.00085 AU (127,000 km; 0.33 LD) | ± 1.408 million km | 1:77 (1.3%) | 3 | −0.53 |
| JPL #39 2025 Jan 30 | 36 (261 obs) | 0.00087 AU (130,000 km; 0.34 LD) | ± 1.408 million km | 1:77 (1.3%) | 3 | −0.53 |
| JPL #40 2025 Jan 31 | 37 (276 obs) | 0.00046 AU (69,000 km; 0.18 LD) | ± 1.2 million km | 1:63 (1.6%) | 3 | −0.47 |
| JPL #41 2025 Feb 1 | 38 (284 obs) | 0.00037 AU (55,000 km; 0.14 LD) | ± 1.119 million km | 1:59 (1.7%) | 3 | −0.43 |
| JPL #42 2025 Feb 2 | 39 (289 obs) | 0.00185 AU (277,000 km; 0.72 LD) | ± 1.049 million km | 1:71 (1.4%) | 3 | −0.52 |
| JPL #43 2025 Feb 3 | 40 (292 obs) | 0.00165 AU (247,000 km; 0.64 LD) | ± 998,000 km | 1:67 (1.5%) | 3 | −0.49 |
| JPL #44 2025 Feb 4 | 41 (294 obs) | 0.00151 AU (226,000 km; 0.59 LD) | ± 981,000 km | 1:63 (1.6%) | 3 | −0.46 |
| JPL #45 2025 Feb 5 | 42 (307 obs) | 0.00116 AU (174,000 km; 0.45 LD) | ± 892,000 km | 1:53 (1.9%) | 3 | −0.40 |
| JPL #46 2025 Feb 6 | 43 (315 obs) | 0.00059 AU (88,000 km; 0.23 LD) | ± 819,000 km | 1:43 (2.3%) | 3 | −0.31 |
| JPL #47 2025 Feb 7 | 43 (325 obs) | 0.00080 AU (120,000 km; 0.31 LD) | ± 792,000 km | 1:45 (2.2%) | 3 | −0.32 |
| JPL #48 2025 Feb 8 | 44 (336 obs) | 0.00061 AU (91,000 km; 0.24 LD) | ± 764,000 km | 1:42 (2.4%) | 3 | −0.29 |
| JPL #49 2025 Feb 9 | 45 (343 obs) | 0.00105 AU (157,000 km; 0.41 LD) | ± 739,000 km | 1:45 (2.2%) | 3 | −0.34 |
| JPL #50 2025 Feb 10 | 45 (347 obs) | 0.00112 AU (168,000 km; 0.44 LD) | ± 712,000 km | 1:48 (2.1%) | 3 | −0.34 |
| JPL #51 2025 Feb 12 | 45 (348 obs) | 0.00114 AU (171,000 km; 0.44 LD) | ± 712,000 km | 1:48 (2.1%) | 3 | −0.35 |
| JPL #53 2025 Feb 13 | 45 (346 obs) | 0.00112 AU (168,000 km; 0.44 LD) | ± 712,000 km | 1:48 (2.1%) | 3 | −0.34 |
| JPL #54 2025 Feb 14 | 45 (354 obs) | 0.00105 AU (157,000 km; 0.41 LD) | ± 707,000 km | 1:45 (2.2%) | 3 | −0.33 |
| JPL #55 2025 Feb 15 | 45 (363 obs) | 0.00105 AU (157,000 km; 0.41 LD) | ± 707,000 km | 1:45 (2.2%) | 3 | −0.33 |
| JPL #56 2025 Feb 17 | 54 (368 obs) | 0.00099 AU (148,000 km; 0.39 LD) | ± 481,000 km | 1:38 (2.6%) | 3 | −0.25 |
| JPL #57 2025 Feb 18 | 55 (370 obs) | 0.00082 AU (123,000 km; 0.32 LD) | ± 458,000 km | 1:32 (3.1%) | 3 | −0.18 |
| JPL #58 2025 Feb 19 | 56 (378 obs) | 0.00145 AU (217,000 km; 0.56 LD) | ± 356,000 km | 1:95 (1.06%) | 3 | −0.66 |
| JPL #59 2025 Feb 19 | 56 (376 obs) | 0.00133 AU (199,000 km; 0.52 LD) | ± 379,000 km | 1:67 (1.5%) | 3 | −0.51 |
| JPL #60 2025 Feb 20 | 57 (391 obs) | 0.00161 AU (241,000 km; 0.63 LD) | ± 291,000 km | 1:370 (0.27%) | 1 | −1.23 |
| JPL #61 2025 Feb 21 | 58 (392 obs) | 0.00153 AU (229,000 km; 0.60 LD) | ± 287,000 km | 1:280 (0.36%) | 1 | −1.11 |
| JPL #62 2025 Feb 22 | 59 (404 obs) | 0.00147 AU (220,000 km; 0.57 LD) | ± 275,000 km | 1:280 (0.36%) | 1 | −1.11 |
| JPL #63 2025 Feb 23 | 60 (418 obs) | 0.00179 AU (268,000 km; 0.70 LD) | ± 207,000 km | 1:26,000 (0.004%) | 0 | −3.08 |
| JPL #64 2025 Feb 24 | 61 (424 obs) | 0.00182 AU (272,000 km; 0.71 LD) | ± 199,000 km | 1:59,000 (0.002%) | 0 | −3.45 |
| JPL #66 2025 Feb 26 | 63 (428 obs) | 0.00180 AU (269,000 km; 0.70 LD) | ± 193,000 km | 1:91,000 (0.001%) | 0 | −3.61 |
| JPL #67 2025 Feb 27 | 63 (440 obs) | 0.00180 AU (269,000 km; 0.70 LD) | ± 192,000 km | 1:91,000 (0.001%) | 0 | −3.61 |
| JPL #68 2025 Feb 28 | 65 (441 obs) | 0.00183 AU (274,000 km; 0.71 LD) | ± 192,000 km | 1:130,000 (0.00076%) | 0 | −3.78 |
| JPL #69 2025 Mar 01 | 66 (442 obs) | 0.00182 AU (272,000 km; 0.71 LD) | ± 191,000 km | 1:120,000 (0.00082%) | 0 | −3.75 |
| JPL #70 2025 Mar 07 | 71 (444 obs) | 0.00180 AU (269,000 km; 0.70 LD) | ± 176,000 km | 1:500,000 (0.0002%) | 0 | −4.36 |
| JPL #71 2025 Mar 08 | 71 (452 obs) | 0.00177 AU (265,000 km; 0.69 LD) | ± 167,000 km | 1:910,000 (0.0001%) | 0 | −4.61 |
| JPL #72 2025 Mar 11 | 71 (453 obs) | 0.00174 AU (260,000 km; 0.68 LD) | ± 159,000 km | 1:1,800,000 (0.000055%) | 0 | −4.93 |
| JPL #73 2025 Mar 13 | 71 (460 obs) | 0.00175 AU (262,000 km; 0.68 LD) | ± 154,000 km | 1:5,000,000 (0.000020%) | 0 | −5.37 |

### Potential Impact effects

A risk corridor of 2024 YR$_4$'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. Using NASA's estimated diameter, mass, and density for 2024 YR$_4$, the asteroid would release energy equivalent to 7.7 megatonnes 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), equivalent to about 500 times the energy released by Little Boy (the atomic bomb dropped on Hiroshima), two and a half times of Grapple Y, 50% of Castle Bravo, or 15% of Tsar Bomba.
Due to its stony composition, this would more likely produce a meteor air burst than an impact crater (for an impact on land) or tsunami (for an oceanic impact). It could cause damage as far as 50 km (30 mi) from the impact site. Despite its potential to cause damage if it were to impact, 2024 YR$_4$ 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.

### Possible impact on the Moon

2024 YR$_4$ has around a 1.7% chance (1-in-58) of impacting a 70% waning gibbous moon on 22 December 2032 around 15:17 to 15:21 UTC. 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), with a 3-sigma uncertainty of 162,000 km (101,000 mi). The Moon has a radius of 1,737 km.
JPL #73 nominal distance from the Moon at 22 December 2032 15:17–15:21 UT Moon Impact Scenario :
| JPL Horizons nominal lunar distance (AU) | uncertainty region (3-sigma) |
| 0.00005 AU (7,500 km; 0.019 LD) | ± 214 thousand km |
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. The impact corridor is a line that extends through the southern parts of Mare Humorum and Mare Nubium.
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.
Evolution of nominal lunar close approach estimates for 2032 :
| Solution | Observation arc (in days) | JPL Horizons nominal lunar distance (AU) | uncertainty region (3-sigma) |
| JPL #30 2025 Jan 22 | 28 (213 obs) | 0.00114 AU (171,000 km; 0.44 LD) | ± 3300000 km |
| JPL #32 2025 Jan 23 | 29 (219 obs) | 0.00000754 AU (1,128 km; 0.00293 LD) | ± 2200000 km |
| JPL #63 2025 Feb 23 | 60 (418 obs) | 0.0000786 AU (11,760 km; 0.0306 LD) | ± 220000 km |
| JPL #64 2025 Feb 24 | 61 (424 obs) | 0.000107 AU (16,000 km; 0.042 LD) | ± 212000 km |
| JPL #66 2025 Feb 26 | 63 (428 obs) | 0.0000902 AU (13,490 km; 0.0351 LD) | ± 205000 km |
| JPL #67 2025 Feb 27 | 63 (440 obs) | 0.0000910 AU (13,610 km; 0.0354 LD) | ± 205000 km |
| JPL #68 2025 Feb 28 | 65 (441 obs) | 0.000126 AU (18,800 km; 0.049 LD) | ± 205000 km |
| JPL #69 2025 Mar 01 | 66 (442 obs) | 0.000113 AU (16,900 km; 0.044 LD) | ± 204000 km |
| JPL #70 2025 Mar 07 | 71 (444 obs) | 0.000091 AU (13,600 km; 0.035 LD) | ± 187000 km |
| JPL #71 2025 Mar 08 | 71 (452 obs) | 0.000054 AU (8,100 km; 0.021 LD) | ± 178000 km |
| JPL #72 2025 Mar 11 | 71 (453 obs) | 0.00002256 AU (3,375 km; 0.00878 LD) | ± 162000 km |
| JPL #73 2025 Mar 13 | 71 (460 obs) | 0.00003719 AU (5,564 km; 0.01447 LD) | ± 162000 km |

## Observation opportunities
### 2025

Additional observations of 2024 YR$_4$ are necessary to reduce uncertainties in its trajectory and determine whether it will impact Earth. 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. The asteroid was not observed between 11–13 January and 8–15 February 2025 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 YR$_4$ at farther distances until 20 May. The JWST is scheduled to observe 2024 YR$_4$ 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 its NIRCam and Mid-Infrared Instrument, which will provide measurements of both 2024 YR$_4$'s position and its infrared thermal emission, from the latter of which the asteroid's size and albedo can be better estimated. NEOWISE burned up in Earth's atmosphere in November 2024, and therefore is not available to observe 2024 YR$_4$.

### Precovery

The orbital uncertainty of 2024 YR$_4$ 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 YR$_4$ 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. The asteroid passed within 12 million km of Earth in September 2016 and within 20 million km of Earth in October 2020. A search through 2016 Subaru Telescope archival images did not find 2024 YR$_4$ in a region where it might have been.
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. 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 YR$_4$ 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 YR$_4$.

### Stellar occultation

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. 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. 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.

### 2028

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. 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 20.83 LD (8.01 million km) away.

## Defense

Had the observations up to 2028 not ruled out a 2032 Earth impact with a 5-sigma confidence, then it might have been useful to send an asteroid deflection mission similar to DART to 2024 YR$_4$ 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 be evacuated.