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2024 YR4

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2024 YR4
2024 YR4 (centered) as tracked by the Very Large Telescope in January 2025
Discovery[1][2]
Discovered byATLAS–CHL (W68)
Discovery siteRio Hurtado, Chile
Discovery date27 December 2024
Designations
2024 YR4
Orbital characteristics[3]
Epoch 17 January 2025 (JD 2460692.5)
Uncertainty parameter 5
Observation arc43 days
Earliest precovery date25 December 2024
Aphelion4.181 AU
Perihelion0.8515 AU
2.5165 AU
Eccentricity0.6616
3.992 yr
(1458.11 days)
13.72°
Inclination3.408°
271.368°
22 November 2024
19 November 2028[4]
21 November 2032[5]
134.364°
Earth MOID0.00276 AU (413,000 km; 1.07 LD)
Jupiter MOID1.271 AU
Physical characteristics
  • 40–90 m (130–300 ft)
  • (est. pV = 0.05–0.25)[6]
  • 54 m (180 ft)
  • (est. pV = 0.154)[7]
0.32440 ± 0.00002 h (19.4640 ± 0.0012 min)[8]
S or L[9]
23 (3 February)
24 (14 February)
23.97±0.28[3]

2024 YR4 is an asteroid between 40 and 90 metres (130 and 300 ft) in diameter, classified as an Apollo-type (Earth-crossing) near-Earth object. It was discovered by the Chilean station of the Asteroid Terrestrial-impact Last Alert System (ATLAS) on 27 December 2024.[2][1] As of 7 February 2025, 2024 YR4 was rated 3 on the Torino scale with a 1 in 45 (2.2%) chance of impacting Earth on 22 December 2032.[7] NASA gives a Palermo Technical Impact Hazard Scale rating of −0.32 for 2024 YR4, which corresponds to an impact hazard of 47.9% of the background hazard level.[7] The discovery has triggered the first step in planetary defense responses, in which all available telescopes are asked to gather data about the object and United Nations-endorsed space agencies are prompted to begin planning for asteroid threat mitigation.[10][11][12]

Preliminary analysis of spectra and photometric timeseries of this asteroid suggests it is a stony S-type or L-type asteroid with a rotation period near 19.5 minutes.[9] The asteroid previously made a close approach of 828,800 kilometres (515,000 miles; 2.156 lunar distances) to Earth on 25 December 2024 (two days before its discovery), and is now moving away from Earth. It will make its next close approach around 17 December 2028.[3] By early April 2025 and until June 2028, 2024 YR4 will have moved too far away from Earth to be observed by ground-based telescopes.[12][13] Space-based infrared telescopes such as the James Webb Space Telescope and the Nancy Grace Roman Space Telescope will be able to observe 2024 YR4 when it is far from Earth.[14]

Physical characteristics

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Size and mass

[edit]
Size comparison of 2024 YR4 and other notable meteoroids, with human-made objects shown for scale

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][15] If 2024 YR4 reflects between 5% and 25% of visible light, then its diameter is between 40 and 90 m (130 and 300 ft).[6] NASA estimates a diameter of 54 m (177 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.[15] The diameter and albedo of 2024 YR4 can only be further constrained with thermal infrared observations, radar observations, or direct imaging by a spacecraft.[13]

The mass and density of 2024 YR4 have not been measured, but the mass can be estimated with an assumed density. NASA estimates a mass of 2.2×108 kg for an assumed density of 2.6 g/cm3, which is a typical density for stony asteroids.[7]

Composition and rotation period

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Preliminary spectroscopic analysis from the Gran Telescopio Canarias and Lowell Discovery Telescope suggests that 2024 YR4 is either an S-type (17% of the asteroid population) or L-type asteroid, both of which points to a stony composition.[9][a]

Photometric observations by the Very Large Telescope (VLT) and the La Silla Observatory's 1.54-meter telescope indicate 2024 YR4 has a rotation period near 19.5 minutes.[9][8] The brightness of 2024 YR4 varies by 0.42 magnitudes as it rotates, indicating it has an elongated shape.[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.[9]

Orbit

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Orbit diagram of 2024 YR4

2024 YR4 orbits the Sun on an elliptical orbit that crosses Earth's orbit, making it an Apollo-type near-Earth object.[3] 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 (ecliptic).[3]

The asteroid came to perihelion (closest approach to the Sun) on 22 November 2024. The asteroid made a close approach to Earth on 25 December 2024, two days before its discovery. During this encounter, the asteroid passed 828,800 km (515,000 mi; 2.156 LD) 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 around 17 December 2028, when it will pass 7,910,000 ± 541,000 km (4,915,000 ± 336,000 mi; 20.58 ± 1.41 LD) from the planet.[3] The 2028 encounter will provide astronomers the opportunity to perform additional observations and extend the observation arc by four years. This will greatly improve calculations of 2024 YR4's orbit in preparation for its close approach around 22 December 2032.[16]

2032 potential impact

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Impact risk corridor for the 2032 approach[16][12]
Animation of 2024 YR4 around Sun - 2032 close approach
  2024 YR4 ·   Sun ·   Mercury ·   Venus ·   Earth ·   Mars

Calculations using the observation arc of 43 days as of 7 February 2025 find that 2024 YR4 has a 1 in 45 (2.2%) chance of impacting Earth on 22 December 2032 around 14:02 UT.[7] The nominal closest approach to Earth is on the 22nd at 11:40 UT (with an uncertainty in the closest approach time of 16 1/3 hours) at a distance of 120,000 kilometres (75,000 miles; 0.31 lunar distances), with a 3-sigma uncertainty of 792,000 km (490,000 mi).[3] Due to 2024 YR4's size and greater-than-1% impact probability, it is rated at Torino scale level 3, which has prompted the International Asteroid Warning Network to issue a notice on 29 January 2025.[12][17] This is the second-highest Torino scale rating an asteroid has ever reached, behind 99942 Apophis which briefly ranked Torino scale level 4 in late 2004.[17] NASA gives a Palermo Technical Impact Hazard Scale rating of −0.32 for 2024 YR4, which corresponds to an impact hazard of 47.9% of the background hazard level.[7] The European Space Agency gives a Palermo rating of −0.29 with an impact probability of 2.25%,[6] while NEODyS gives −0.31 with an impact probability of 2.04%.[18] The risk corridor of 2024 YR4's possible impact locations runs from the Pacific Ocean to Northern South America, the Atlantic Ocean, central Africa, a corner of the Arabian peninsula, and then to northern India.[16][12]

JPL #47 nominal distance for the 22 December 2032 14:02 UT Virtual Impactor Scenario
JPL Horizons
nominal geocentric
distance (AU) 		uncertainty
region
(3-sigma)
0.0011 AU (160,000 km; 0.43 LD)[19] ± 1.1 million km[19]
Evolution of nominal 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 ( 87obs) 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)[b] ± 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)[c] ± 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) 0.00005 AU (7,500 km; 0.019 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

Impact effect

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Using NASA's estimated diameter, mass, and density for 2024 YR4, the asteroid would release energy equivalent to 7.7 megatonnes of TNT (32 petajoules) if it were to impact Earth at a velocity at atmosphere entry of 17.32 km/s (10.76 mi/s).[7] This would more likely produce a meteor air burst, or less likely produce an impact crater. It could cause destruction as far as 50 km (30 mi) from the impact site.[15][17]

Observation opportunities

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Additional observations of 2024 YR4 are necessary to reduce uncertainties in its trajectory and determine whether it will impact Earth.[12] Because the asteroid is now moving away from Earth, it is becoming fainter, necessitating the use of larger aperture telescopes such as the 8.2-meter Keck telescope and the Very Large Telescope.[13] By early April 2025 and until June 2028, 2024 YR4 will have moved too far away from Earth to be observed by even the largest ground-based telescopes.[13] Space-based infrared telescopes such as the James Webb Space Telescope (JWST) will be able to observe 2024 YR4 when it is farther from Earth.[13] The JWST is scheduled to observe 2024 YR4 in March and May 2025 using its NIRCam and Mid-Infrared Instrument, which will provide measurements of both 2024 YR4's position and infrared thermal emission, the latter from which the asteroid's size and albedo can be better estimated.[14][20]

The orbital uncertainty of 2024 YR4 may be further reduced with precovery observations, in which the asteroid may 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 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 longer exposure than would have been optimal for observations of such a fast moving asteroid.[21][d] 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 of a region where 2024 YR4 might have been did not find it.[16] According to Sam Deen,[23] including this negative precovery data in the orbit calculation decreases the likelihood that the asteroid is somewhere along 60–80% of the non-impacting trajectories calculated from the observation arc to late January, which he estimated raised 2024 YR4's impact probability to 3% at that time; also including the single poorer-quality 25 December 2024 precovery observation increased the probability to 6%.[21] Deen said "I invite people to double check me because it's been just me looking at this. I could have missed something." 2016 images of the region from Palomar Observatory, not made public as of January 2025, may provide further information.[16]

It may be possible to observe a stellar occultation by 2024 YR4, which if detected can significantly constrain the asteroid's position and trajectory and also provide a direct measurement of its diameter via timing chords(s). 2024 YR4 was predicted to occult an apparent magnitude 11.1 star on 6 February 2025, but the path of the asteroid's penumbral shadow on Earth was highly uncertain, with as of 1 February 2025 a positional uncertainty of roughly 7.3 km (4.5 mi) and many times the expected width of the shadow.[24][e] Fresnel diffraction of the occulted star's light around the small 2024 YR4 also reduced by how much the occultation would have dimmed the star.[24]

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 about magnitude 25 when it comes to opposition around 19 July 2028 at an Earth distance of 0.79 AU (118 million km). However, 2024 YR4's 2028 approach will not bring it close enough for precise radar observations.[12] If a 2032 impact could not be ruled out, then an asteroid redirect mission similar to DART could be sent to 2024 YR4 to avert its impact.[25]

Notes

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  1. ^ C-type asteroids are about 75% of the asteroid population, S-type asteroids are about 17%, and M-type asteroids (iron–nickel) are about 5%.
  2. ^ JPL #30 with a 28-day observation arc had an uncertainty of almost ± 3 days for the Earth close approach date in 2032.[3]
  3. ^ JPL #32 The nominal orbit is 1,129 km from the Moon, which is less than the Moon's radius of 1,737.
  4. ^ The 25 December 2024 observation has a high RMS of 1.6 arcseconds in right ascension and 0.7 arcseconds in declination.[22]
  5. ^ David Dunham reported that the formal uncertainty in 2024 YR4's path location on Earth was 25 times larger than the diameter. The long side of the uncertainty of the occulted star was 28.7mas."[24] For this event 1mas=0.3s, 1km=1.4s. The uncertainty of 28.7mas corresponded to a time uncertainty of 8.61s, and 8.61s corresponded to a distance of 6.15km. A diameter of 55m was assumed for the asteroid. Multiplying that by 25 gives 1.3km, and 6.15km+1.3km=7.45km.

References

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  1. ^ a b "2024 YR4". Minor Planet Center. Retrieved 27 January 2025.
  2. ^ a b Minor Planet Center Staff (27 December 2024). "Mpec 2024-Y140 : 2024 Yr4". Minor Planet Electronic Circular. 2024-Y140. Minor Planet Center. Bibcode:2024MPEC....Y..140W. doi:10.48377/MPEC/2024-Y140. Retrieved 27 January 2025.
  3. ^ a b c d e f g h i j "JPL Small-Body Database Lookup: (2024 YR4)" (2025-02-06 last obs.). Jet Propulsion Laboratory. Archived from the original on 22 January 2025. Retrieved 6 February 2025.(See archive for JPL #30 solution)
  4. ^ "2028 Perihelion" (Perihelion occurs when rdot flips from negative to positive). JPL Horizons. Archived from the original on 2 February 2025. Retrieved 1 February 2025.
  5. ^ "2032 Perihelion" (Perihelion occurs when rdot flips from negative to positive). JPL Horizons. 7 February 2025. Retrieved 7 February 2025.
  6. ^ a b c "2024YR4". Near-Earth Objects Coordination Centre. European Space Agency. 7 February 2025. Retrieved 7 February 2025.
  7. ^ a b c d e f g h i "(2024 YR4) – Earth Impact Risk Summary". Center for Near-Earth Object Studies. NASA. 7 February 2025. Archived from the original on 28 January 2025.
  8. ^ a b c Pravec, Petr. "'Prepublished' periods of asteroids". Ondrejov Asteroid Photometry Project. Astronomical Institute of the Czech Academy of Sciences. Archived from the original on 30 January 2025. Retrieved 29 January 2025.
  9. ^ a b c d e "2024 YR4". International Asteroid Warning Network. 29 January 2025. Archived from the original on 30 January 2025. Retrieved 29 January 2025.
  10. ^ Sample, Ian (30 January 2025). "Asteroid triggers global defence plan amid chance of collision with Earth in 2032". The Guardian. Retrieved 30 January 2025.
  11. ^ Andrews, Robin George (29 January 2025). "Astronomers Are Keeping an Eye on This Asteroid's Odds of Hitting Earth". The New York Times. Archived from the original on 30 January 2025. Retrieved 30 January 2025.
  12. ^ a b c d e f g "International Asteroid Warning Network (IAWN) Potential Asteroid Impact Notification" (PDF). International Asteroid Warning Network. 29 January 2025. Archived (PDF) from the original on 30 January 2025. Retrieved 29 January 2025.
  13. ^ a b c d e "Asteroid 2024 YR4 reaches level 3 on the Torino Scale". Center for Near-Earth Object Studies. NASA. 31 January 2025. Retrieved 1 February 2025.
  14. ^ a b Andrews, Robin George (5 February 2025). "This asteroid may hit Earth in 2032. Don't panic—scientists have a plan". National Geographic. Retrieved 5 February 2025.
  15. ^ a b c Lea, Robert (28 January 2025). "Astronomers discover 196-foot asteroid with 1-in-83 chance of hitting Earth in 2032". Space.com. Archived from the original on 28 January 2025. Retrieved 28 January 2025.
  16. ^ a b c d e Chandler, David L. (28 January 2025). "Newly Discovered Asteroid Has Slight Chance of Earth Impact in 2032". skyandtelescope.org. Retrieved 28 January 2025.
  17. ^ a b c Whitt, Kelly Kizer (27 January 2025). "Asteroid 2024 YR4 has non-zero odds of hitting Earth". EarthSky. Archived from the original on 28 January 2025. Retrieved 27 January 2025.
  18. ^ "2024YR4 Impactor Table". NEODyS-2. University of Pisa. 7 February 2025. Retrieved 7 February 2025.
  19. ^ a b "JPL Horizons: 2024 YR4 geocentric distance and uncertainty at 22 Dec 2032 14:02 UT". JPL Horizons. Archived from the original on 3 February 2025. Retrieved 5 February 2025.
  20. ^ Rivkin, Andrew S.; et al. (5 February 2025). "Size Measurements of a Potential Earth-Impacting Asteroid with JWST MIRI and NIRCAM". JWST Proposal (9239). Space Telescope Science Institute. Retrieved 5 February 2025.
  21. ^ a b Deen, Sam (27 January 2025). "2024 YR4: Torino scale 3, negative observations, 3–6% impact?". Minor Planets Mailing List. Retrieved 27 January 2025.
  22. ^ "2024YR4 Observational Details". NEODyS-2. University of Pisa. Retrieved 30 January 2025.
  23. ^ "Sam Deen, private investigator of Solar System bodies from California". Stefan Kürti's Astro Web. 20 May 2024. Archived from the original on 22 July 2024. Retrieved 30 January 2025.
  24. ^ a b c Herald, Dave (31 January 2025). "Re: 2024 YR4 occultation on Feb 6 and later..." International Occultation Timing Association (IOTA) Mailing List. Retrieved 31 January 2025.
  25. ^ O'Callaghan, Jonathan (31 January 2025). "Newfound Asteroid May Hit Earth in 2032, Scientists Say". Scientific American. Archived from the original on 1 February 2025. Retrieved 1 February 2025.
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