(29075) 1950 DA

Radar image of 1950 DA taken at Arecibo in March 2001, from a distance of 22 LD or 0.052 AU
Discovery[1]
Discovered by	Carl A. Wirtanen
Discovery site	Lick Obs.
Discovery date	23 February 1950
Designations
MPC designation	(29075) 1950 DA
Alternative designations	1950 DA · 2000 YK66
Minor planet category	NEO · Apollo · PHA[1][2] · risk listed
Orbital characteristics[2]
Epoch 31 January 2012 (JD 2455957.5)
Uncertainty parameter 0
Observation arc	67.96 yr (24,823 d)
Aphelion	2.5619 AU
Perihelion	0.8350 AU
Semi-major axis	1.6985 AU
Eccentricity	0.5083
Orbital period (sidereal)	2.21 yr (809 d)
Mean anomaly	315.94°
Mean motion	0° 26m 43.08s / day
Inclination	12.175°
Longitude of ascending node	356.74°
Argument of perihelion	224.61°
Earth MOID	0.0406 AU (15.8169 LD)
Proper orbital elements[3]
Precession of perihelion	13.655 arcsec / yr
Precession of the ascending node	−35.824 arcsec / yr
Physical characteristics
Dimensions	1.39 km × 1.46 km × 1.07 km[4]
Mean diameter	1.1 km[4][5] 1.25±0.12 km[4] 2.00±0.20 km[6]
Mass	>4×1012 kg[a]
Mean density	>3.5 g/cm3[4]
Synodic rotation period	2.12160±0.00004 h[4]
Geometric albedo	0.070[6] 0.25[7]
Spectral type	S[8][9] EM[10] B–V = 0.862±0.077[8] V–R = 0.494±0.069[8] V–I = 0.816±0.067[8]
Absolute magnitude (H)	17.00[6] 17.1[1][2] 17.55±0.3 (R)[10][9] 18.0[9][4]

(29075) 1950 DA, provisional designation 1950 DA, is a risk–listed asteroid, classified as a near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 1.1 kilometers (0.68 miles) in diameter.^[4] It once had the highest known probability of impacting Earth.^[11] In 2002, it had the highest Palermo rating with a value of 0.17 for a possible collision in 2880.^[12] Since that time, the estimated risk has been updated several times. In December 2015, the odds of an Earth impact were revised to 1 in 8,300 (0.012%) with a Palermo rating of −1.42.^[11] As of 2022, It is listed on the Sentry Risk Table with the second highest cumulative Palermo rating of −2.05 (impact risk of 1-in-34,000).^[13][14] 1950 DA is not assigned a Torino scale rating, because the 2880 date is over 100 years in the future.

Discovery and nomenclature

1950 DA was first discovered on 23 February 1950 by Carl A. Wirtanen at Lick Observatory.^[2] It was observed for seventeen days^[5] and then lost because this short observation arc resulted in large uncertainties in Wirtanen's orbital solution. On 31 December 2000, it was recovered at Lowell Observatory and was announced as 2000 YK₆₆ on 4 January 2001.^[15] Just two hours later it was recognized as 1950 DA.^[5][16]

Observations

Asteroid 1950 DA, Arecibo Observatory radar image (coloured version)

Arecibo radar movie of 1950 DA obtained during 48 minutes (37% of a rotation) on 4 March 2001

On 5 March 2001, 1950 DA made a close approach to Earth at a distance of 0.05207 AU (7.790 million km; 4.840 million mi; 20.26 LD).^[17] It was studied by radar at the Goldstone and Arecibo observatories from March 3 to 7, 2001.^[5]

The studies showed that the asteroid has a mean diameter of 1.1 km, assuming that 1950 DA is a retrograde rotator.^[18] 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, 1950 DA is thought to be fairly dense (more than 3.5 g/cm³, assuming that it has no internal strength) and likely composed of nickel–iron.^[4] In August 2014, scientists from the University of Tennessee determined that 1950 DA is a rubble pile rotating faster than the breakup limit for its density, implying the asteroid is held together by van der Waals forces rather than gravity.^[19][20]

1950 DA made a distant approach to Earth on 5 February 2021.^[17] However, at that time it was half an AU away from Earth, preventing more useful astrometrics and timing that occurs when an object is closer to Earth. The next close approach that presents a good opportunity to observe the asteroid will be on 2 March 2032, when it will be 0.075 AU (11.2 million km) from Earth. The following table lists next five approaches closer than 0.10 AU.^[17] By 2136 the close approach solutions are becoming notably more divergent.

Possible Earth impact

That 1950 DA has one of the best-determined asteroid orbital solutions is due to a combination of:^[5]

• an orbit moderately inclined (12 degrees)^[2] to the ecliptic plane (reducing in-plane perturbations);
• high-precision radar astrometry, which provides its distance and is complementary to the measurements of angular positions;
• a 68-year observation arc;^[2]
• an uncertainty region controlled by resonance.^[5]

Main-belt asteroid 78 Diana (~125 km in diameter) will pass about 0.003 AU (450,000 km; 280,000 mi) from 1950 DA on 5 August 2150.^[5] At that distance and size, Diana will perturb 1950 DA enough so that the change in trajectory is notable by 2880 (730 years later). In addition, over the intervening time, 1950 DA's rotation will cause its orbit to slightly change as a result of the Yarkovsky effect. If 1950 DA continues on its present orbit, it may approach Earth on 16 March 2880, though the mean trajectory passes many millions of kilometres from Earth, so 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 8,300 (0.012%).^[11]

The energy released by a collision with an object the size of 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.