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(29075) 1950 DA

Arecibo radio telescope radar image of 1950 DA taken on March 3, 2001, from a distance of 0.052 AU (22 lunar distances)
Discovery
Discovered by	Carl A. Wirtanen
Discovery date	February 23, 1950
Designations
Alternative names	2000 YK66
Minor planet category	Apollo, PHA
Orbital characteristics
Epoch 2011-Aug-27 (JD 2455800.5) (Uncertainty=0)
Aphelion	2.5618 AU (383.23 Gm)
Perihelion	0.83529 AU (124.95 Gm)
Semi-major axis	1.6985 AU (254.09 Gm)
Eccentricity	0.50823
Orbital period (sidereal)	808.59 d (2.21 yr)
Average orbital speed	21.30 km/s
Mean anomaly	246.03°
Inclination	12.175°
Longitude of ascending node	356.74°
Argument of perihelion	224.59°
Physical characteristics
Dimensions	1.39 x 1.46 x 1.07 km; mean: 1.1 km
Mass	>4×10 kg
Mean density	>3.5 g/cm³
Surface gravity	<0 at equator bulge, due to fast rotation
Synodic rotation period	0.0884 d (2.1216 h)
Albedo	0.07
Spectral type	E or M
Absolute magnitude (H)	17.1 17.55R

(29075) 1950 DA is a near-Earth asteroid. Among asteroids more than 1 km in diameter, it is notable for having the highest known probability of impacting Earth. In 2002, it had the highest Palermo rating with a value of 0.17 for a possible collision in 2880. Since that time, the estimated risk has been updated several times. In December of 2015, the odds of an Earth impact were revised to 1 in 8,330 (0.012%) with a Palermo rating of −1.42. (29075) 1950 DA is not assigned a Torino scale rating, because the 2880 date is over 100 years in the future.

Discovery and name

(29075) 1950 DA was first discovered on February 23, 1950, by Carl A. Wirtanen at Lick Observatory. It was observed for seventeen days and then lost because the short observation arc resulted in large uncertainties in Wirtanen's orbital solution. On December 31, 2000, it was recovered as 2000 YK₆₆ and two hours later was recognized as (29075) 1950 DA.

Observations

On March 5, 2001, (29075) 1950 DA made a close approach to Earth of 0.0520726 AU (7,789,950 km; 4,840,450 mi). It was studied by radar at the Goldstone and Arecibo observatories from March 3 to 7, 2001.

The studies showed that the asteroid has a mean diameter of 1.1 km, assuming that (29075) 1950 DA is a retrograde rotator. Optical lightcurve analysis by Lenka Sarounova and Petr Pravec shows that its rotation period is 2.1216 ± 0.0001 hours. Due to its short rotation period and high radar albedo, (29075) 1950 DA is thought to be fairly dense (more than 3.5 g/cm³) and likely composed of nickel–iron. In August 2014, scientists from the University of Tennessee determined that (29075) 1950 DA is a rubble pile that is kept together by van der Waals forces.

Possible Earth impact

That (29075) 1950 DA has one of the best-determined asteroid orbital solutions is due to a combination of:

• an orbit moderately inclined (12 degrees) to the ecliptic plane (reducing in-plane perturbations);
• high-precision radar astrometry, which provides its distance and is complementary to visual-wavelength measurements of angular positions;
• a 64-year observation arc;
• an uncertainty region controlled by resonance.

Main-belt asteroid 78 Diana (~125 km in diameter) will pass about 0.003 AU (450,000 km; 280,000 mi) from (29075) 1950 DA on August 5, 2150. At that distance and size, Diana will perturb (29075) 1950 DA enough so that the change in trajectory is notable by 2880 (730 years later). In addition, over the intervening time, (29075) 1950 DA's rotation will cause its orbit to slightly change as a result of the Yarkovsky effect. If (29075) 1950 DA continues on its present orbit, it may approach Earth on March 16, 2880, though the mean trajectory passes many millions of kilometers from Earth, so (29075) 1950 DA does not have a significant chance of impacting Earth. As of the 7 December 2015 solution, the probability of an impact in 2880 is 1 in 8,330 (0.012%). (A collision is likely to be ruled out as more data becomes available).

The energy released by a collision with an object the size of (29075) 1950 DA would cause major effects on the climate and biosphere, which would be devastating to human civilization. The discovery of the potential impact heightened interest in asteroid deflection strategies.

See also

• List of notable asteroids
• Torino Scale
• Palermo scale

References

1. ^ "JPL Small-Body Database Browser: 29075 (1950 DA)" (last observation: 2010-10-04; arc: 60.61 years). Jet Propulsion Laboratory. Retrieved November 19, 2011.
2. "MPEC 2001-A26 : 1950 DA = 2000 YK66". IAU Minor Planet Center. January 4, 2001. Retrieved November 19, 2011. (K00Y66K)
3. ^ "Physical modeling of near-Earth Asteroid (29075) 1950 DA" (PDF). NASA/JPL Near-Earth Object Program Office. May 4, 2007. Retrieved May 27, 2015.
4. A reported volume of 1.14 km³ * density of 3.5 g/cm³ yields a mass (m=d*v) of 3.99×10 kg.
5. ^ "NeoDys Near Earth Objects Dynamic Site" (Physical Info). Retrieved May 27, 2015.
6. ^ "Sentry Risk Table". NASA/JPL Near-Earth Object Program Office. December 9, 2014. Retrieved December 10, 2014.
7. "Asteroid 1950 DA". NASA/JPL Near-Earth Object Program Office. Archived from the original on July 21, 2011. Retrieved October 14, 2011.
8. ^ Giorgini, J. D.; Ostro, S. J; Benner, L. A. M.; Chodas, P.W.; Chesley, S.R.; Hudson, R. S.; et al. (2002). "Asteroid 1950 DA's Encounter With Earth in 2880: Physical Limits of Collision Probability Prediction" (PDF). Science. 296 (5565): 132–136. Bibcode:2002Sci...296..132G. doi:10.1126/science.1068191. PMID 11935024.
9. "JPL Close-Approach Data: 29075 (1950 DA)" (last observation: 2010-10-04; arc: 60.61 years). Retrieved November 19, 2011.
10. Cite error: The named reference Farnocchia2013 was invoked but never defined (see the help page).
11. "UT Research uncovers forces that hold asteroid together". U of Tennessee. Retrieved August 17, 2015.
12. "29075 (1950 DA) Earth Impact Risk Summary". NASA/JPL Near-Earth Object Program Office. August 19, 2014. Retrieved March 1, 2015.

External links

(29075) 1950 DA at the JPL Small-Body Database

• Close approach · Discovery · Ephemeris · Orbit viewer · Orbit parameters · Physical parameters

• 3D model Rotating model of the asteroid

• Apollo asteroids
• Potential impact events caused by near-Earth objects
• Astronomical objects discovered in 1950
• Numbered asteroids
• Potentially hazardous asteroids