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2012 DA14
Goldstone radar collage of 2012 DA14 on 15–16 February 2013.
Discovery[1]
Discovered byOAM Observatory, La Sagra (J75)
0.45-m Reflector
Discovery dateFebruary 23, 2012
Designations
Designation
2012 DA14
Post 2013-Feb-15: Aten[2][3]
Pre-2013: Apollo NEO[2]
Orbital characteristics[3]
Epoch 2013-Apr-18
(Uncertainty=0)[3]
Aphelion0.9917 AU (Q)
Perihelion0.8289 AU (q)
0.9103 AU (a)
Eccentricity0.0894
317.2 days
231.0° (M)
Inclination11.60°
146.9°
195.5°
Physical characteristics
Dimensions~45 meters (148 ft)[4]
20 m × 40 m (66 ft × 131 ft) (elongated)[5][6]
(Geometric mean = 18 m)
18 meters (59 ft)[7]
~0.014 meters (0.55 in) per second
9 hr[5][7][8]
Albedo0.44 ± 0.20[7]
Spectral type
L-type[5][7]
7.2 (2013 peak)[9]
24.1[3]
25.29 HV; 24.5 HR [7]
24.4 (2012 estimate)[4]

2012 DA14 is a near-Earth asteroid with an estimated diameter of 30 meters (98 ft) and an estimated mass of 40,000 metric tons. Before radar imaging, estimates for the diameter were 45–50 meters.[4] During its 2013 close passage, the asteroid passed 27,700 km (17,200 mi), or 4.3 Earth radii, from the surface of Earth.[2] This is a record close approach for a known object of this size.[2] About 16 hours before the closest approach of 2012 DA14, an asteroid entered Earth's atmosphere above Russia, which was, however, unrelated to it because it had a significantly different orbit.[10][11][12]

Discovery and past risk assessments

The asteroid was discovered on February 23, 2012, by the Observatorio Astronómico de La Sagra, Granada in Spain (J75),[1] operated remotely by astronomers in Mallorca, seven days after passing 0.0174 AU (2,600,000 km; 1,620,000 mi) from Earth.[3]

Based on the still relatively imprecise orbit deduced from the short arc of the 2012 observations, there was a cumulative 0.033% risk estimate (1 in 3,030) of 2012 DA14 impacting Earth sometime between 2026 and 2069.[4] It was, on the other hand, already clear that the asteroid would pass no closer to Earth's surface than 3.2 Earth radii during its 2013 passage.[13] Eliminating an entry on the Sentry Risk Table is a negative prediction; a prediction of where it will not be.

Orbital shift

During closest approach to Earth in 2013 the orbital period of the asteroid was reduced from 366 days to 317 days.[14] Its aphelion was reduced from 1.110 to 0.9917 AU, leaving it almost entirely inside Earth's orbit.

Parameter Epoch aphelion
(Q) 		perihelion
(q) 		Semi-major
axis
(a) 		eccentricity
(e) 		Period
(p) 		inclination
(i) 		Longitude
ascending
node
(Ω) 		Mean
anomaly
(M) 		Argument
of
perihelion
(ω)
Units AU (days) (°)
Pre-flyby 2012-Sep-30 1.110 0.8935 1.001 0.1081 366.2 10.33° 147.2° 299.9° 271.0°
Post-flyby 2013-Apr-18 0.9917 0.8289 0.9103 0.0894 317.2 11.60° 146.9° 231.0° 195.5°

2013 passage

Diagram of 2012 DA14 passing Earth on 15 February 2013
Closest approach of asteroid drawn to scale

On January 9, 2013, the asteroid was observed again by Las Campanas Observatory and the observation arc increased from 79 days to 321 days.[15] On February 15, 2013 at 19:25 Universal Time, the asteroid passed 0.0002276 AU (34,050 km; 21,160 mi) from the center of Earth,[3] with an uncertainty region of about 0.0000001 AU (15 km; 9.3 mi).[3] It passed 27,743 kilometers (17,239 mi) above Earth's surface,[2] closer than satellites in geosynchronous orbit.[2] It briefly peaked at an apparent magnitude of roughly 7.2, a factor of a few fainter than would have been visible to the naked eye.[9][13] The best observation location for the closest approach was Indonesia.[2] Eastern Europe, Asia, and Australia also were well situated to observe the asteroid during its closest approach.[2] The asteroid was not expected to pass any closer than 1950 km to any satellites.[16] Goldstone Observatory observed 2012 DA14 with radar from February 16 to February 20.[5][17] Radar observations have shown it to be an elongated asteroid with dimensions of 20 by 40 meters (66 by 131 feet).[18] This gives the asteroid a geometric mean (spherical) diameter equivalent to 28 meters (92 ft).

During the close approach an observational campaign involving 5 different telescopes in 4 different observatories was carried on in order to get information on the physical properties of this NEO.[7] Visible and near-Infrared photometry, and visible spectroscopy were obtained at Gran Telescopio Canarias, Telescopio Nazionale Galileo and Calar Alto Observatory and put together. The classification using the M4AST online tool says this is an L-type asteroid those peculiar asteroids are characterized by a strongly reddish spectrum shortward of 0.8 μm, and a featureless flat spectrum longward of this, with little or no concave-up curvature related to a 1 μm silicon absorption band. Time-series photometry was also obtained in the Observatorio de La Hita (I95)[1] and Observatorio de Sierra Nevada during two consecutive nights (15–16 February 2013). All of this data were co-fased to build a light curve of the object. This light-curve is double-peak and presents large variations in magnitude, implying a very elongated object, which is compatible with radar observations.[5] The amplitude of the light-curve yields an axial ratio that assuming a long axis of 40 m, as can be inferred from the radar images by Goldstone, results in an equivalent diameter of 18 m, much smaller than the estimations before the close-approach. The rotational period was precisely determined from the light curve obtaining a value of 8.95 ± 0.08 h. This value is confirmed with an analysis of all the photometry of this objects reported to the Minor Planet Center. Using data pre and post close approach the authors find that the object suffered a spin-up during the event that decreased the rotational period form 9.8 ± 0.1 h down to 8.8 ± 0.1, which is compatible with the more accurate value estimated form the light-curve.

The close approach to Earth reduced the orbital period of 2012 DA14 from 368 days to 317 days,[2][14] and perturbed it from the Apollo class to the Aten class of near-Earth asteroids.[2] Its next close approach to Earth will be on 15 February 2046 when it will pass about 0.0148 AU (2,210,000 km; 1,380,000 mi) from Earth.[3] Based on 7 radar observations, the next close approach to Earth similar to the 2013 passage will be on 16 February 2123 when 2012 DA14 will pass no closer than 0.0002 AU (30,000 km; 19,000 mi) from the center of Earth.[3] For the 2123 passage, the nominal pass will be 0.003 AU (450,000 km; 280,000 mi) from the center of the Moon and then 0.005 AU (750,000 km; 460,000 mi) from the center of Earth.[3]


Risks

Two-body simulation of the Sun and 2012 DA14 during the 2013 Earth approach, N-body perturbations are not considered
  • The uncertainty region of 2012 DA14 during planetary encounters is now well determined through 2123.[3]
  • 2012 DA14 was removed from the Sentry Risk Table on 16 February 2013.[19]
  • It is estimated that there are more than a million near-Earth asteroids smaller than 100 meters.[20]

Risk assessments were calculated based on a diameter of 45 meters and a mass of 130,000 metric tons.[4] It was estimated that, if it were ever to impact Earth, it would enter the atmosphere at a speed of 12.7 km/s, would have a kinetic energy equivalent to 2.4 megatons of TNT,[4] and would produce an air burst with the equivalent of 2.1 megatons of TNT[21] at an altitude of roughly 10.1 kilometers (33,000 ft).[21] The Tunguska event has been estimated at 3–20 megatons.[22] Asteroids of approximately 50 meters in diameter are expected to impact Earth once every 1200 years or so.[23] Asteroids larger than 35 meters across can pose a threat to a town or city.[24] As a result of radar observations it is now known that 2012 DA14 is only about 30 meters in diameter.[5]

Airburst estimates for a stony asteroid with a diameter ranging from 30 to 85 meters[21]
Diameter Kinetic energy at
atmospheric entry		 Airburst
energy		 Airburst
altitude		 Average
frequency
30 m (98 ft) 708 kt 530 kt 16.1 km (53,000 ft) 185 years
50 m (160 ft) 3.3 Mt 2.9 Mt 8.5 km (28,000 ft) 764 years
70 m (230 ft) 9 Mt 8.5 Mt 3.4 km (11,000 ft) 1900 years
85 m (279 ft) 16.1 Mt 15.6 Mt 0.435 km (1,430 ft) 3300 years

The table above uses Sentry's stony asteroid density of 2600 kg/m3, Sentry's atmospheric entry velocity (Vimpact) of 12.7 km/s,[4] and an angle of 45 degrees.

For kinetic energy at atmospheric entry, 3.3 Mt is equivalent to DF-4, 9 Mt is equivalent to Ivy Mike and 15.6 Mt is equivalent to Castle Bravo. For airburst energy, 530 kt is equivalent to W88 and 2.9 Mt is equivalent to R-12 Dvina.

See also

References

  1. ^ a b c "MPEC 2012-D51 : 2012 DA14". IAU Minor Planet Center. 2012-02-24. Retrieved 2012-03-05. (K12D14A)
  2. ^ a b c d e f g h i j Paul Chodas and Don Yeomans (February 1, 2013). "Asteroid 2012 DA14 To Pass Very Close to the Earth on February 15, 2013". NASA/JPL Near-Earth Object Program Office. Retrieved 2013-02-01.
  3. ^ a b c d e f g h i j k "JPL Close-Approach Data: (2012 DA14)". 2013-02-19 last obs (arc=362 days (Radar=7 obs); Uncertainty=0). Retrieved 2013-02-19. {{cite web}}: Check date values in: |date= (help)
  4. ^ a b c d e f g "WayBack Machine archive from 25 Aug 2012". Wayback Machine. 2012-08-25. Retrieved 2013-01-10.
  5. ^ a b c d e f Dr. Lance A. M. Benner (2013-01-13). "2012 DA14 Goldstone Radar Observations Planning". NASA/JPL Asteroid Radar Research. Retrieved 2013-01-15.
  6. ^ "L. Johnson 2012 DA14 Update: radar images showing elongated object ~20x40m". Minor Planet Center.
  7. ^ a b c d e f de Leon, J.; Ortiz, J. L.; Pinilla-Alonso, N.; Cabrera-Lavers, A.; et al. (2013). "Visible and near-infrared observations of asteroid 2012 DA14 during its closest approach of February 15th, 2013". Astronomy and Astrophysics. 555: L2–L6. arXiv:1303.0554. Bibcode:2013A&A...555L...2D. doi:10.1051/0004-6361/201321373. {{cite journal}}: Explicit use of et al. in: |author2= (help)CS1 maint: multiple names: authors list (link)
  8. ^ Bruce L. Gary (2013.02.18). "Asteroid "2012 DA14" Rotation Light Curve". Retrieved 2013-02-20. {{cite web}}: Check date values in: |date= (help); External link in |author= (help)
  9. ^ a b "2012 DA14 Ephemerides for 15 February 2013". NEODyS (Near Earth Objects – Dynamic Site). Retrieved 2013-01-10.
  10. ^ Don Yeomans and Paul Chodas (March 1, 2013). "Additional Details on the Large Fireball Event over Russia on Feb. 15, 2013". NASA/JPL Near-Earth Object Program Office. Retrieved 2013-03-02.
  11. ^ "Russia Meteor Not Linked to Asteroid Flyby". NASA. Retrieved 15 February 2013.
  12. ^ "Russian Asteroid Strike". ESA.int. Retrieved 16 February 2013.
  13. ^ a b Paul Chodas, Jon Giorgini & Don Yeomans (March 6, 2012). "Near-Earth Asteroid 2012 DA14 to Miss Earth on February 15, 2013". NASA/JPL Near-Earth Object Program Office. Retrieved 2012-03-06.
  14. ^ a b Horizons output. "Horizon Online Ephemeris System". Retrieved 2013-01-10. ("Ephemeris Type: Elements" PR value)
  15. ^ "2012 DA14 Orbit". Minor Planet Center. 2013 01 09 (arc=321 days). Retrieved 2013-01-11. {{cite web}}: Check date values in: |date= (help)
  16. ^ "Closest approaches of 2012 DA14 to known satellites - no encounter is closer than ~2000 km". Jonathan's Space Report No. 674. 2013-02-10. Retrieved 2013-02-11.
  17. ^ SPACE DAILY
  18. ^ Phil Plait (2013-02-19). "An Asteroid's Parting Shot". Bad Astronomy blog. Retrieved 2013-02-19.
  19. ^ "Date/Time Removed". NASA/JPL Near-Earth Object Program Office. Retrieved 2013-02-16.
  20. ^ "WISE Revises Numbers of Asteroids Near Earth". NASA/JPL. September 29, 2011. Retrieved 2012-03-06.
  21. ^ a b c Robert Marcus, H. Jay Melosh, and Gareth Collins (2010). "Earth Impact Effects Program". Imperial College London / Purdue University. Retrieved 2013-02-09.{{cite web}}: CS1 maint: multiple names: authors list (link) (solution using 45 meters, 2600 kg/m3, 12.7 km/s, 45 degrees)
  22. ^ "Sandia supercomputers offer new explanation of Tunguska disaster". Sandia National Laboratories. 2007-12-17. Retrieved 2007-12-22.
  23. ^ "Record Setting Asteroid Flyby". NASA Science. Jan. 28, 2013. Retrieved 2013-01-29. {{cite web}}: Check date values in: |date= (help)
  24. ^ Will Ferguson (January 22, 2013). "Asteroid Hunter Gives an Update on the Threat of Near-Earth Objects". Scientific American. Retrieved 2013-01-23.
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