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Post Info TOPIC: Asteroid (1566) Icarus
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Title: Asteroid 1566 Icarus' size, shape, orbit, and Yarkovsky drift from radar observations
Author: Adam H. Greenberg, Jean-Luc Margot, Ashok K. Verma, Patrick A. Taylor, Shantanu P. Naidu, Marina. Brozovic, Lance A. M. Benner

Near-Earth asteroid (NEA) 1566 Icarus (a=1.08 au, e=0.83, i=22.8°) made a close approach to Earth in June 2015 at 22 lunar distances (LD). Its detection during the 1968 approach (16 LD) was the first in the history of asteroid radar astronomy. A subsequent approach in 1996 (40 LD) did not yield radar images. We describe analyses of our 2015 radar observations of Icarus obtained at the Arecibo Observatory and the DSS-14 antenna at Goldstone. These data show that the asteroid has an equivalent diameter of 1.44 km with 18% uncertainties, resolving long-standing questions about the asteroid size. We also solve for Icarus' spin axis orientation (Lambda=270°±10°,Beta=-81°±10°), which is not consistent with the estimates based on the 1968 lightcurve observations. Icarus has a strongly specular scattering behaviour, among the highest ever measured in asteroid radar observations, and a radar albedo of ~2%, among the lowest ever measured in asteroid radar observations. The low cross-section suggests a high-porosity surface, presumably related to Icarus' cratering, spin, and thermal histories. Finally, we present the first use of our orbit determination software for the generation of observational ephemerides, and we demonstrate its ability to determine subtle perturbations on NEA orbits by measuring Icarus' orbit-averaged drift in semi-major axis ((-4.62±0.48) x 10^-4 au/My, or ~60 m per revolution). Our Yarkovsky rate measurement resolves a discrepancy between two published rates that did not include the 2015 radar astrometry.

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The 1000 metre wide asteroid (1566) Icarus will make a close pass (21.0 LD, 0.0538 AU) in the constellation Ursa Major, travelling at 30.22 km/second, to the Earth-Moon system on the 16th June 2015 @ 15:39 UT ±00:01. 

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The Lunar Distance (LD), the distance between Earth and the Moon, equals 384,401 km, (or 0.00256 AU).

Ephemeris

Date    TT    R. A. (2000) Decl.     Delta      r     Elong.  Phase     Mag
2014 06 15    20 33 13.2 -29 31 54   0.5614  1.4869   139.3    26.5    17.7
2014 06 16    20 28 29.2 -30 07 37   0.5618  1.4957   141.2    25.2    17.7
2014 06 17    20 23 38.7 -30 42 37   0.5625  1.5044   143.2    23.9    17.7
2014 06 18    20 18 42.3 -31 16 50   0.5636  1.5129   145.1    22.6    17.6
2014 06 19    20 13 40.4 -31 50 07   0.5650  1.5214   147.0    21.3    17.6
2014 06 20    20 08 33.4 -32 22 24   0.5668  1.5298   148.9    20.1    17.6
2014 06 21    20 03 22.0 -32 53 36   0.5690  1.5381   150.8    18.8    17.6
2014 06 22    19 58 06.7 -33 23 37   0.5716  1.5462   152.6    17.6    17.6
2014 06 23    19 52 48.2 -33 52 22   0.5745  1.5543   154.4    16.4    17.5
2014 06 24    19 47 27.3 -34 19 48   0.5779  1.5623   156.1    15.3    17.5
2014 06 25    19 42 04.5 -34 45 52   0.5816  1.5702   157.7    14.2    17.5
2014 06 26    19 36 40.7 -35 10 29   0.5858  1.5780   159.2    13.2    17.5
2014 06 27    19 31 16.7 -35 33 38   0.5903  1.5857   160.7    12.2    17.5
2014 06 28    19 25 53.2 -35 55 18   0.5953  1.5933   162.0    11.4    17.5
2014 06 29    19 20 31.0 -36 15 27   0.6006  1.6008   163.1    10.6    17.5
2014 06 30    19 15 10.9 -36 34 05   0.6063  1.6082   164.0    10.0    17.5


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Apollo asteroid (1566) Icarus makes its closest approach to the Earth (0.561 AU) on the 14th June 2014

Ephemeris

Date    TT    R. A. (2000) Decl.     Delta      r     Elong.  Phase     Mag
2014 06 13    20 42 21.0 -28 18 44   0.5617  1.4691   135.3    29.1    17.8
2014 06 14    20 37 50.6 -28 55 34   0.5614  1.4780   137.3    27.8    17.7
2014 06 15    20 33 13.2 -29 31 54   0.5614  1.4869   139.3    26.5    17.7
2014 06 16    20 28 29.2 -30 07 37   0.5618  1.4957   141.2    25.2    17.7
2014 06 17    20 23 38.7 -30 42 37   0.5625  1.5044   143.2    23.9    17.7
2014 06 18    20 18 42.3 -31 16 50   0.5636  1.5129   145.1    22.6    17.6
2014 06 19    20 13 40.4 -31 50 07   0.5650  1.5214   147.0    21.3    17.6
2014 06 20    20 08 33.4 -32 22 24   0.5668  1.5298   148.9    20.1    17.6
2014 06 21    20 03 22.0 -32 53 36   0.5690  1.5381   150.8    18.8    17.6
2014 06 22    19 58 06.7 -33 23 37   0.5716  1.5462   152.6    17.6    17.6
2014 06 23    19 52 48.2 -33 52 22   0.5745  1.5543   154.4    16.4    17.5
2014 06 24    19 47 27.3 -34 19 48   0.5779  1.5623   156.1    15.3    17.5
2014 06 25    19 42 04.5 -34 45 52   0.5816  1.5702   157.7    14.2    17.5
2014 06 26    19 36 40.7 -35 10 29   0.5858  1.5780   159.2    13.2    17.5
2014 06 27    19 31 16.7 -35 33 38   0.5903  1.5857   160.7    12.2    17.5
2014 06 28    19 25 53.2 -35 55 18   0.5953  1.5933   162.0    11.4    17.5
2014 06 29    19 20 31.0 -36 15 27   0.6006  1.6008   163.1    10.6    17.5
2014 06 30    19 15 10.9 -36 34 05   0.6063  1.6082   164.0    10.0    17.5


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Asteroid (1566) Icarus makes its closest approach to the Earth (0.698 AU) on the 7th April 2014 

Ephemeris

Date    TT    R. A. (2000) Decl.     Delta      r     Elong.  Phase    Mag
2014 04 05    23 11 48.3 +05 07 09   0.6987  0.4787    25.7   115.1    19.0
2014 04 06    23 07 39.1 +04 35 27   0.6980  0.5014    27.7   112.0    18.9
2014 04 07    23 03 48.7 +04 04 00   0.6978  0.5236    29.6   109.2    18.8
2014 04 08    23 00 15.7 +03 32 58   0.6980  0.5455    31.5   106.6    18.8
2014 04 09    22 56 58.7 +03 02 25   0.6983  0.5671    33.3   104.2    18.7
2014 04 10    22 53 56.3 +02 32 25   0.6989  0.5882    35.1   101.9    18.7
2014 04 11    22 51 07.3 +02 03 00   0.6995  0.6090    36.8    99.7    18.7
2014 04 12    22 48 30.6 +01 34 12   0.7002  0.6295    38.5    97.7    18.6
2014 04 13    22 46 04.9 +01 06 00   0.7009  0.6496    40.1    95.8    18.6
2014 04 14    22 43 49.2 +00 38 22   0.7016  0.6694    41.7    94.0    18.6
2014 04 15    22 41 42.7 +00 11 19   0.7022  0.6888    43.3    92.3    18.6
2014 04 16    22 39 44.5 -00 15 12   0.7027  0.7079    44.9    90.7    18.6
2014 04 17    22 37 53.6 -00 41 13   0.7031  0.7268    46.4    89.1    18.6
2014 04 18    22 36 09.4 -01 06 46   0.7034  0.7453    47.9    87.7    18.6
2014 04 19    22 34 31.3 -01 31 53   0.7035  0.7635    49.4    86.3    18.6
2014 04 20    22 32 58.5 -01 56 37   0.7035  0.7815    50.8    85.0    18.6
2014 04 21    22 31 30.4 -02 20 59   0.7033  0.7992    52.2    83.7    18.6
2014 04 22    22 30 06.5 -02 45 03   0.7029  0.8166    53.7    82.5    18.6
2014 04 23    22 28 46.4 -03 08 51   0.7024  0.8338    55.1    81.3    18.6
2014 04 24    22 27 29.4 -03 32 24   0.7017  0.8507    56.4    80.1    18.6
2014 04 25    22 26 15.2 -03 55 46   0.7008  0.8674    57.8    79.0    18.6
2014 04 26    22 25 03.3 -04 18 59   0.6997  0.8838    59.2    77.9    18.6
2014 04 27    22 23 53.3 -04 42 05   0.6985  0.9000    60.6    76.9    18.6
2014 04 28    22 22 44.8 -05 05 06   0.6971  0.9160    61.9    75.9    18.6
2014 04 29    22 21 37.6 -05 28 05   0.6955  0.9317    63.3    74.9    18.6
2014 04 30    22 20 31.2 -05 51 04   0.6937  0.9472    64.6    73.9    18.6


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Asteroid 1566 Icarus makes its closest approach to the Earth (0.996 AU) on the 20th July, 2012



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Asteroid 1566 Icarus Close Encounter with Earth 16 Jun 2015



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Apollo asteroid 1566 Icarus makes a close approach to Earth at gaps of 9, 19, or 38 years. Rarely, it comes as close as 6.4 Gm (16 lunar distances and 4 million miles), as it did on June 14, 1968. The last close approach was in 1996, at 15.1 Gm, almost 40 times as far as the Moon. The next close approach will be June 16, 2015, at 8.1 Gm.
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At 12:26 p.m. on June 19, 1968 the asteroid Icarus, which is nearly a mile in diameter, will crash into the mid-Atlantic, 2,000 miles east of Florida. Its impact - the equivalent of a 500,000-megaton bomb blast - will splash out some 1,000 cubic miles of sea water and form a crater 15 miles across in the ocean floor. Tidal waves 100 ft. high will sweep across coastal cities on both sides of the ocean, and earthquakes 100 times worse than any ever recorded will be felt all over the world.
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1566 Icarus is an Apollo asteroid (a sub-class of near-Earth asteroid) that at perihelion comes closer to the Sun than Mercury, i.e. it is a Mercury-crossing asteroid. It is also a Venus and Mars-crosser. It is named after Icarus of Greek mythology, who flew too close to the Sun. It was discovered in 1949 by Walter Baade.
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