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2024 YR4

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2024 YR4
2024 YR4 (center) 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 October 2024 (JD 2460600.5)
Uncertainty parameter 5
Observation arc38 days
Earliest precovery date25 December 2024
Aphelion4.226 AU
Perihelion0.8528 AU
2.5392 AU
Eccentricity0.6642
4.046 yr
(1477.87 days)
351.08°
Inclination3.453°
271.412°
22 November 2024
19 November 2028[4]
134.642°
Earth MOID0.00265 AU (396 thousand km; 1.03 LD)
Jupiter MOID1.228 AU
Physical characteristics
  • 40–100 m (130–330 ft)
  • (est. pV = 0.05–0.25)[5]
  • 55 m (180 ft)
  • (est. pV = 0.154)[6]
0.32440 ± 0.00002 h (19.4640 ± 0.0012 min)[7]
S or L[8]
23.96±0.272[3]

2024 YR4 is an asteroid between 40 and 100 metres (130 and 330 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 1 February 2025, 2024 YR4 was rated 3 on the Torino scale with a 1 in 59 (1.7%) chance of impacting Earth on 22 December 2032.[6] NASA gives a Palermo Technical Impact Hazard Scale rating of −0.43 for 2024 YR4, which corresponds to an impact hazard of 37.2% of the background hazard level.[6] 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.[9][10][11]

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.[8] 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.[11][12] Space-based infrared telescopes such as the James Webb Space Telescope may be able to observe 2024 YR4 when it is far from Earth.[12][13] 2024 YR4 will occult a magnitude 11.4 star on 6 February 2025, although the asteroid's location on that date is highly uncertain 5.1~12.7km.[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).[6][15] If 2024 YR4 reflects between 5% and 25% of visible light, then its diameter is between 40 and 100 m (130 and 330 ft).[5] NASA estimates a diameter of 55 m (180 ft) for an assumed geometric albedo of 0.154.[6] 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.[12]

The mass and density of 2024 YR4 have not been measured, but 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 common density for stony asteroids.[6]

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.[8][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.[8][7] The brightness of 2024 YR4 varies by 0.42 magnitudes as it rotates, indicating it has an elongated shape.[7] 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.[8]

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 4.05 years and an orbital inclination of 3.45 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 7,920,000 ± 960,000 km (4,920,000 ± 600,000 mi; 20.6 ± 2.5 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][11]

Calculations using the observation arc of 38 days as of 1 February 2025 find that 2024 YR4 has a 1 in 59 (1.7%) chance of impacting Earth on 22 December 2032 around 14:02 UT.[6] The nominal closest approach to Earth is on the 22nd at 13:00 UT (with an uncertainty in the closest approach time of 22.5 hours) at a distance of 54,729 kilometres (34,007 miles; 0.14237 lunar distances), with a 3-sigma uncertainty of 1.119 million km (0.70 million mi).[3] Due to 2024 YR4's large 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.[11][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 −0.43 for 2024 YR4, which corresponds to an impact hazard of 37.2% of the background hazard level.[6] The European Space Agency gives a Palermo rating of −0.42 with an impact probability of 1.62%,[5] while NEODyS gives −0.37 with an impact probability of 1.71%.[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, and then to northern India.[16][11]

Using NASA's estimated diameter, mass, and density for 2024 YR4, the asteroid would release energy equivalent to 7.8 megatonnes of TNT (33 petajoules) if it were to impact Earth at a speed of 17.32 km/s (10.76 mi/s).[6] This would produce either a meteor air burst or an impact crater, and cause destruction as far as 50 km (30 mi) from the impact site.[15][17]

The earliest known pre-discovery observation of 2024 YR4 was 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 asteroid observations.[19][b] 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,[21] 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%.[19] 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] 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 likelihood of impact in 2032. Should an impact by 2032 not be ruled out, then a mission similar to DART could be sent to avert an impact.[13]

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 1 -1.73

2024 Dec 31

3 (71 obs) 1:920 1 -1.66

2025 Jan 1

4 ( 87obs) 1:870 1 -1.64

2025 Jan 2

6 (109 obs) 1:842 1 -1.63

2025 Jan 3

7 (120 obs) 1:760 1 -1.61
JPL #14

2025 Jan 6

8 (145 obs) 0.01706 AU (2,552 thousand km; 6.64 LD) ± 9.62 million km 1:730 1
JPL #15

2025 Jan 6

11 (158 obs) 0.01537 AU (2,299 thousand km; 5.98 LD) ± 9.55 million km 1:710 1 -1.53

2025 Jan 11

14 (170 obs) 1:630 1 -1.53
JPL #27

2025 Jan 20

26 (198 obs) 1:320 1
JPL #30

2025 Jan 22

28 (213 obs) 0.00068 AU (102 thousand km; 0.26 LD) ± 3.37 million km 1:190 1 -0.93
JPL #32

2025 Jan 23

29 (219 obs) 0.00171 AU (256 thousand km; 0.67 LD) ± 2.28 million km 1:110 1 -0.69
JPL #34

2025 Jan 24

30 (227 obs) 0.00113 AU (169 thousand km; 0.44 LD) ± 1.96 million km 1:110 1 -0.69
JPL #35

2025 Jan 27

33 (238 obs) 0.00005 AU (7.5 thousand km; 0.019 LD) ± 1.605 million km 1:83 3 -0.57
JPL #36

2025 Jan 28

34 (245 obs) 0.00071 AU (106 thousand km; 0.28 LD) ± 1.55 million km 1:83 3 -0.56
JPL #37

2025 Jan 29

35 (257 obs) 0.00085 AU (127 thousand km; 0.33 LD) ± 1.408 million km 1:77 3 -0.53
JPL #39

2025 Jan 30

36 (261 obs) 0.00087 AU (130 thousand km; 0.34 LD) ± 1.408 million km 1:77 3 -0.53
JPL #40

2025 Jan 31

37 (276 obs) 0.00046 AU (69 thousand km; 0.18 LD) ± 1.2 million km 1:63 3 -0.47
JPL #41

2025 Feb 1

38 (284 obs) 0.00037 AU (55 thousand km; 0.14 LD) ± 1.119 million km 1:59 3 -0.43

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. ^ The 25 December 2024 observation has a high RMS of 1.6 arcseconds in right ascension and 0.7 arcseconds in declination.[20]

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. 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 "JPL Small-Body Database Lookup: (2024 YR4)" (2025-01-30 last obs.). Jet Propulsion Laboratory. Archived from the original on 23 February 2023. Retrieved 30 January 2025.
  4. ^ "2028 Perihelion" (Perihelion occurs when rdot flips from negative to positive). JPL Horizons. Retrieved 1 February 2025.
  5. ^ a b c "2024YR4". Near-Earth Objects Coordination Centre. European Space Agency. 30 January 2025. Retrieved 30 January 2025.
  6. ^ a b c d e f g h i "(2024 YR4) – Earth Impact Risk Summary". Center for Near-Earth Object Studies. NASA. 30 January 2025. Archived from the original on 28 January 2025. Updated frequently.
  7. ^ a b c Pravec, Petr. "'Prepublished' periods of asteroids". Ondrejov Asteroid Photometry Project. Astronomical Institute of the Czech Academy of Sciences. Retrieved 29 January 2025. Updated regularly.
  8. ^ a b c d e "2024 YR4". International Asteroid Warning Network. 29 January 2025. Retrieved 29 January 2025.
  9. ^ Sample, Ian (30 January 2025). "Asteroid triggers global defence plan amid chance of collision with Earth in 2032". The Guardian. Retrieved 30 January 2025.
  10. ^ Andrews, Robin George (29 January 2025). "Astronomers Are Keeping an Eye on This Asteroid's Odds of Hitting Earth". The New York Times. Retrieved 30 January 2025.
  11. ^ a b c d e "International Asteroid Warning Network (IAWN) Potential Asteroid Impact Notification" (PDF). International Asteroid Warning Network. 29 January 2025. Retrieved 29 January 2025.
  12. ^ a b c "Asteroid 2024 YR4 reaches level 3 on the Torino Scale". Center for Near-Earth Object Studies. NASA. 31 January 2025. Retrieved 1 February 2025.
  13. ^ a b O'Callaghan, Jonathan (31 January 2025). "Newfound Asteroid May Hit Earth in 2032, Scientists Say". Scientific American. Retrieved 1 February 2025.
  14. ^ 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.
  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. 31 January 2025. Retrieved 31 January 2025. Date of computation=20250131 182804.019 CET
  19. ^ 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.
  20. ^ "2024YR4 Observational Details". NEODyS-2. University of Pisa. Retrieved 30 January 2025.
  21. ^ "Sam Deen, private investigator of Solar System bodies from California". Stefan Kürti's Astro Web. 20 May 2024.


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