Astronomy:588 Achilles

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Short description: Jupiter trojan
588 Achilles
Image: 300 pixels
Modelled shape of Achilles from its light curve
Discovery [1]
Discovered byM. F. Wolf
Discovery siteHeidelberg Obs.
Discovery date22 February 1906
Designations
(588) Achilles
Pronunciation/əˈkɪlz/
Named afterAchilles (Greek mythology)[2]
1906 TG
Minor planet categoryJupiter trojan[1][3]
Greek [4] · background[5]
AdjectivesAchillean /ˌækɪˈlən, əˈkɪliən/[6]
Orbital characteristics[3]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc112.25 yr (41,000 d)
|{{{apsis}}}|helion}}5.9714 AU
|{{{apsis}}}|helion}}4.4467 AU
5.2091 AU
Eccentricity0.1463
Orbital period11.89 yr (4,343 d)
Mean anomaly205.11°
Mean motion0° 4m 58.44s / day
Inclination10.318°
Longitude of ascending node316.54°
133.50°
Jupiter MOID0.5704 AU
TJupiter2.9460
Physical characteristics
Mean diameter130.10±0.55 km[7]
133.22±3.33 km[8]
135.47±4.1 km[9]
Rotation period7.306±0.002 h[10][11]
Geometric albedo0.0328±0.002[9]
0.035±0.002[8]
0.043±0.006[7]
Tholen = DU [3][12]
B–V = 0.755[3]
U–B = 0.216[3]
V–I = 0.940±0.019[12]
Absolute magnitude (H)8.47[7]
8.67[1][3][8][9]


Achilles (minor planet designation: 588 Achilles) is a large Jupiter trojan asteroid of the Greek camp. Achilles was the first Jupiter trojan to be discovered, and was discovered by Max Wolf at the Heidelberg Observatory in 1906. Wolf named the minor planet after the legendary hero Achilles from Greek mythology.[1][2] The dark D-type asteroid measures approximately 133 kilometers (83 miles) in diameter which makes it one of the 10 largest Jupiter trojans. It has a rotation period of 7.3 hours and possibly a spherical shape.[12]

Discovery

Achilles was discovered on 22 February 1906, by the German astronomer Max Wolf at the Heidelberg-Königstuhl State Observatory in southern Germany. It was the first discovery of a Jupiter trojan, although (12126) 1999 RM11 had been observed as A904 RD two years previously. This body, however, remained unconfirmed as the observation period was not long enough to calculate an orbit. August Kopff, a colleague of Wolf at Heidelberg, then discovered 617 Patroclus eight months after Achilles, and, in early 1907, he discovered the largest of all Jupiter trojans, 624 Hektor.[13]

Orbit and classification

Achilles orbits the Sun at a distance of 4.4–6.0 AU in the L4 Lagrangian point of the SunJupiter System once every 11 years and 11 months (4,343 days; semi-major axis of 5.21 AU). Its orbit shows an eccentricity of 0.15 and an inclination of 10 degrees from the plane of the ecliptic.[3]

Achilles is the first known example of the stable solution of the three-body problem worked out by French mathematician Joseph Lagrange in 1772, after whom the minor planet 1006 Lagrangea is named. After the discovery of other asteroids with similar orbital characteristics, which were also named after heroes from the Trojan War (see below), the term "Trojan asteroids" or "Jupiter trojans" became commonly used.[2] In addition, a rule was established that the L4 point was the "Greek camp", whereas the L5 point was the "Trojan camp", though not before each camp had acquired a "spy" (Hektor in the Greek camp and Patroclus in the Trojan camp).

Physical characteristics

Spectral type

In the Tholen taxonomic scheme, Achilles is classified as a D-type asteroid with an unusual spectrum (DU).[3] Its V–I color index of 0.94 is typical for most larger Jupiter trojans (see table below).

Photometry

Achilles' rotation period of 7.3 hours is somewhat shorter than that of most other large Jupiter trojans but close to that of 911 Agamemnon, 3451 Mentor and 3317 Paris, which are similar in size (see table below). Its low brightness amplitude is indicative of a rather spherical shape.[12] From July 2007 until September 2008, coordinated photometric observations were carried out by astronomers at Simeiz (Crimea), Rozhen (Bulgaria), Maidanak (Uzbekistan) and Kharkiv (Ukraine) observatories.[10][14] Analysis of the obtained lightcurves determined a period of 7.306±0.002 hours with a brightness amplitude of 0.02–0.11 magnitude ({{{1}}}).[12] Alternative period determinations by Cláudia Angeli (7.0 h), Robert Stephens (7.312 h), Stefano Mottola (7.32 h) and Vincenzo Zappalà (12 h) are mostly in good agreement ({{{1}}}).[12][15][14][16][17]

Diameter and albedo

According to the surveys carried out by the Infrared Astronomical Satellite, IRAS, the Japanese Akari satellite, and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, the body's surface has a very low albedo in the range of 0.0328 to 0.043, making its absolute magnitude of approximately 8.57 correspond to a diameter of 130.1 to 135.5 kilometers.[9][8][7]

Achilles is the 6th largest Jupiter trojan according to IRAS and Akari, and the 4th largest based on NEOWISE data:

100+ largest Jupiter trojans
Largest Jupiter Trojans by survey(A)
(mean-diameter in kilometers; YoD: Year of Discovery)
Designation H WISE IRAS Akari Ln RP V–I YoD Ref
624 Hektor 7.2 225 233 230.99 L4 6.92 0.930 1907 list
617 Patroclus 8.19 140.362 140.92 140.85 L5 102.80 0.830 1906 list
911 Agamemnon 7.89 131.038 166.66 185.30 L4 6.59 0.980 1919 list
588 Achilles 8.67 130.099 135.47 133.22 L4 7.31 0.940 1906 list
3451 Mentor 8.4 126.288 116.30 117.91 L5 7.70 0.770 1984 list
3317 Paris 8.3 118.790 116.26 120.45 L5 7.09 0.950 1984 list
1867 Deiphobus 8.3 118.220 122.67 131.31 L5 58.66 0.930 1971 list
1172 Äneas 8.33 118.020 142.82 148.66 L5 8.71 0.950 1930 list
1437 Diomedes 8.3 117.786 164.31 172.60 L4 24.49 0.810 1937 list
1143 Odysseus 7.93 114.624 125.64 130.81 L4 10.11 0.860 1930 list
2241 Alcathous 8.64 113.682 114.63 118.87 L5 7.69 0.940 1979 list
659 Nestor 8.99 112.320 108.87 107.06 L4 15.98 0.790 1908 list
3793 Leonteus 8.7 112.046 86.26 87.58 L4 5.62 0.780 1985 list
3063 Makhaon 8.4 111.655 116.14 114.34 L4 8.64 0.830 1983 list
1583 Antilochus 8.6 108.842 101.62 111.69 L4 31.54 0.950 1950 list
884 Priamus 8.81 101.093 96.29 119.99 L5 6.86 0.900 1917 list
1208 Troilus 8.99 100.477 103.34 111.36 L5 56.17 0.740 1931 list
1173 Anchises 8.89 99.549 126.27 120.49 L5 11.60 0.780 1930 list
2207 Antenor 8.89 97.658 85.11 91.32 L5 7.97 0.950 1977 list
2363 Cebriones 9.11 95.976 81.84 84.61 L5 20.05 0.910 1977 list
4063 Euforbo 8.7 95.619 102.46 106.38 L4 8.85 0.950 1989 list
2357 Phereclos 8.94 94.625 94.90 98.45 L5 14.39 0.960 1981 list
4709 Ennomos 8.5 91.433 80.85 80.03 L5 12.28 0.690 1988 list
2797 Teucer 8.7 89.430 111.14 113.99 L4 10.15 0.920 1981 list
2920 Automedon 8.8 88.574 111.01 113.11 L4 10.21 0.950 1981 list
(15436) 1998 VU30 9.1 87.646 85.71 78.63 L4 8.97 0.870 1998 list
3596 Meriones 9.2 87.380 75.09 73.28 L4 12.96 0.830 1985 list
2893 Peiroos 9.23 86.884 87.46 86.76 L5 8.96 0.950 1975 list
4086 Podalirius 9.1 85.495 86.89 85.98 L4 10.43 0.870 1985 list
4060 Deipylos 9.3 84.043 79.21 86.79 L4 9.30 0.760 1987 list
1404 Ajax 9.3 83.990 81.69 96.34 L4 29.38 0.960 1936 list
4348 Poulydamas 9.5 82.032 70.08 87.51 L5 9.91 0.840 1988 list
5144 Achates 9.0 80.958 91.91 89.85 L5 5.96 0.920 1991 list
4833 Meges 8.9 80.165 87.33 89.39 L4 14.25 0.940 1989 list
2223 Sarpedon 9.41 77.480 94.63 108.21 L5 22.74 0.880 1977 list
(4489) 1988 AK 9.0 76.595 92.93 95.02 L4 12.58 0.950 1988 list
2260 Neoptolemus 9.31 76.435 71.65 81.28 L4 8.18 0.950 1975 list
5254 Ulysses 9.2 76.147 78.34 80.00 L4 28.72 0.970 1986 list
(3708) 1974 FV1 9.3 75.661 79.59 76.75 L5 6.55 0.980 1974 list
2674 Pandarus 9.1 74.267 98.10 101.72 L5 8.48 1.000 1982 list
3564 Talthybius 9.4 73.730 68.92 74.11 L4 40.59 0.900 1985 list
4834 Thoas 9.1 72.331 86.82 96.21 L4 18.19 0.950 1989 list
(7641) 1986 TT6 9.4 71.839 68.97 75.28 L4 27.77 0.980 1986 list
3540 Protesilaos 9.3 70.225 76.84 87.66 L4 8.95 0.940 1973 list
(11395) 1998 XN77 9.8 68.977 64.71 67.78 L4 17.38 1998 list
(4035) 1986 WD 9.6 68.733 68.23 66.99 L4 13.47 0.970 1986 list
5264 Telephus 9.4 68.472 73.26 81.38 L4 9.53 0.970 1991 list
1868 Thersites 9.5 68.163 70.08 78.89 L4 10.48 0.960 1960 list
(9799) 1996 RJ 9.6 68.033 64.87 72.42 L4 21.52 0.910 1996 list
4068 Menestheus 9.5 67.625 62.37 68.46 L4 14.40 0.950 1973 list
(23135) 2000 AN146 9.9 66.230 58.29 68.50 L4 8.69 0.860 2000 list
2456 Palamedes 9.3 65.916 91.66 99.60 L4 7.24 0.920 1966 list
3709 Polypoites 9.1 65.297 99.09 85.23 L4 10.04 1.000 1985 list
1749 Telamon 9.5 64.898 81.06 69.14 L4 16.98 0.970 1949 list
3548 Eurybates 9.6 63.885 72.14 68.40 L4 8.71 0.730 1973 list
4543 Phoinix 9.7 63.836 62.79 69.54 L4 38.87 1.200 1989 list
12444 Prothoon 9.8 63.835 64.31 62.41 L5 15.82 1996 list
4836 Medon 9.5 63.277 67.73 78.70 L4 9.82 0.920 1989 list
(16070) 1999 RB101 9.7 63.191 64.13 68.98 L5 20.24 0.960 1999 list
(15440) 1998 WX4 9.6 62.519 66.48 71.88 L4 21.43 0.970 1998 list
(4715) 1989 TS1 9.7 62.097 63.91 65.93 L5 8.81 0.850 1989 list
(34746) 2001 QE91 9.8 61.684 60.51 63.63 L5 19.63 0.950 2001 list
(38050) 1998 VR38 9.8 61.603 61.04 50.44 L4 18.85 0.990 1998 list
5130 Ilioneus 9.7 60.711 59.40 52.49 L5 14.77 0.960 1989 list
5027 Androgeos 9.6 59.786 57.86 n.a. L4 11.38 0.910 1988 list
(6090) 1989 DJ 9.4 59.568 74.53 81.92 L4 18.48 0.980 1989 list
(5648) 1990 VU1 9.7 59.295 63.91 n.a. L5 37.56 0.900 1990 list
7119 Hiera 9.7 59.150 76.40 77.29 L4 400 0.950 1989 list
4805 Asteropaios 10.0 57.647 53.16 43.44 L5 12.37 1990 list
16974 Iphthime 9.8 57.341 55.43 57.15 L4 78.9 0.960 1998 list
4867 Polites 9.8 57.251 58.29 64.29 L5 11.24 1.010 1989 list
2895 Memnon 10.0 56.706 55.67 n.a. L5 7.50 0.710 1981 list
4708 Polydoros 9.9 54.964 55.67 n.a. L5 7.52 0.960 1988 list
(21601) 1998 XO89 10.0 54.909 55.67 56.08 L4 12.65 0.970 1998 list
(12929) 1999 TZ1 9.9 54.077 61.04 55.34 L5 9.27 0.880 1999 list
17492 Hippasos 10.0 53.975 55.67 n.a. L5 17.75 1991 list
5652 Amphimachus 10.1 53.921 53.16 52.48 L4 8.37 1.050 1992 list
2759 Idomeneus 9.9 53.676 61.01 52.55 L4 32.38 0.910 1980 list
(5258) 1989 AU1 10.2 53.275 50.77 n.a. L4 19.85 1.010 1989 list
(12126) 1999 RM11 10.1 53.202 n.a. n.a. L5 n.a. ? 1999 list
(15502) 1999 NV27 10.0 53.100 55.67 50.86 L5 15.13 0.875 1999 list
4754 Panthoos 10.0 53.025 53.15 56.96 L5 27.68 1977 list
4832 Palinurus 10.0 52.058 53.16 n.a. L5 5.32 1.000 1988 list
5126 Achaemenides 10.5 51.922 44.22 48.57 L4 53.02 1989 list
3240 Laocoon 10.2 51.695 50.77 n.a. L5 11.31 0.880 1978 list
4902 Thessandrus 9.8 51.263 61.04 71.79 L4 738 0.960 1989 list
11552 Boucolion 10.1 51.136 53.16 53.91 L5 32.44 1993 list
(20729) 1999 XS143 10.4 50.961 46.30 n.a. L4 5.72 1.000 1999 list
(6545) 1986 TR6 10.1 50.951 53.16 n.a. L4 16.26 0.910 1986 list
4792 Lykaon 10.1 50.870 53.16 n.a. L5 40.09 0.960 1988 list
21900 Orus 10.0 50.810 55.67 53.87 L4 13.45 0.950 1999 list
1873 Agenor 10.1 50.799 53.76 54.38 L5 20.60 1971 list
5028 Halaesus 10.2 50.770 50.77 n.a. L4 24.94 0.900 1988 list
2146 Stentor 9.9 50.755 58.29 n.a. L4 16.40 1976 list
4722 Agelaos 10.0 50.378 53.16 59.47 L5 18.44 0.910 1977 list
5284 Orsilocus 10.1 50.159 53.16 n.a. L4 10.31 0.970 1989 list
11509 Thersilochos 10.1 49.960 53.16 56.23 L5 17.37 1990 list
5285 Krethon 10.1 49.606 58.53 52.61 L4 12.04 1.090 1989 list
4791 Iphidamas 10.1 49.528 57.85 59.96 L5 9.70 1.030 1988 list
9023 Mnesthus 10.1 49.151 50.77 60.80 L5 30.66 1988 list
5283 Pyrrhus 9.7 48.356 64.58 69.93 L4 7.32 0.950 1989 list
4946 Askalaphus 10.2 48.209 52.71 66.10 L4 22.73 0.940 1988 list
(22149) 2000 WD49 10.2 48.190 50.77 50.37 L4 7.84 1.090 2000 list
(32496) 2000 WX182 10.2 48.017 50.77 51.63 L5 23.34 0.950 2000 list
5120 Bitias 10.2 47.987 50.77 n.a. L5 15.21 0.780 1988 list
12714 Alkimos 10.1 47.819 61.04 54.62 L4 28.48 1991 list
(7352) 1994 CO 9.9 47.731 55.67 47.07 L5 648 0.850 1994 list
1870 Glaukos 10.6 47.649 42.23 n.a. L5 5.99 1971 list
4138 Kalchas 10.1 46.462 53.16 61.04 L4 29.2 0.810 1973 list
(23958) 1998 VD30 10.2 46.001 50.77 47.91 L4 562 0.990 1998 list
4828 Misenus 10.4 45.954 46.30 43.22 L5 12.87 0.920 1988 list
4057 Demophon 10.1 45.683 53.16 n.a. L4 29.82 1.060 1985 list
4501 Eurypylos 10.4 45.524 46.30 n.a. L4 6.05 1989 list
4007 Euryalos 10.3 45.515 48.48 53.89 L4 6.39 1973 list
5259 Epeigeus 10.3 44.741 42.59 44.42 L4 18.42 1989 list
30705 Idaios 10.4 44.546 46.30 n.a. L5 15.74 1977 list
16560 Daitor 10.7 43.861 51.42 43.38 L5 1991 list
(15977) 1998 MA11 10.4 43.530 46.30 51.53 L5 250 0.906 1998 list
7543 Prylis 10.6 42.893 42.23 n.a. L4 17.80 1973 list
4827 Dares 10.5 42.770 44.22 n.a. L5 19.00 1988 list
1647 Menelaus 10.5 42.716 44.22 n.a. L4 17.74 0.866 1957 list
(A) Used sources: WISE/NEOWISE catalog (NEOWISE_DIAM_V1 PDS, Grav, 2012); IRAS data (SIMPS v.6 catalog); and Akari catalog (Usui, 2011); RP: rotation period and V–I (color index) taken from the LCDB

Note: missing data was completed with figures from the JPL SBDB (query) and from the LCDB (query form) for the WISE/NEOWISE and SIMPS catalogs, respectively. These figures are given in italics. Also, listing is incomplete above #100.

Naming

This minor planet's name was suggested by Austrian astronomer Johann Palisa. It was named after Achilles, the legendary hero from Greek mythology and central figure in Homer's Iliad which tells the accounts of the Trojan War (also see 5700 Homerus and 6604 Ilias). As an infant, Achilles was plunged in the River Styx by his mother Thetis (also see 17 Thetis), thus rendering his body invulnerable excepting the heel by which he was held. He slew Hector (see also 624 Hektor), the greatest Trojan warrior. He was eventually killed by an arrow in the heel by Paris (see 3317 Paris).[2]

References

  1. 1.0 1.1 1.2 1.3 "588 Achilles (1906 TG)". Minor Planet Center. https://www.minorplanetcenter.net/db_search/show_object?object_id=588. 
  2. 2.0 2.1 2.2 2.3 Schmadel, Lutz D. (2007). "(588) Achilles". Dictionary of Minor Planet Names. Springer Berlin Heidelberg. p. 61. doi:10.1007/978-3-540-29925-7_589. ISBN 978-3-540-00238-3. 
  3. 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 "JPL Small-Body Database Browser: 588 Achilles (1906 TG)". Jet Propulsion Laboratory. https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2000588. 
  4. "List of Jupiter Trojans". Minor Planet Center. 20 June 2016. https://www.minorplanetcenter.net/iau/lists/JupiterTrojans.html. 
  5. "Asteroid (588) Achilles – Proper elements". AstDyS-2, Asteroids – Dynamic Site. https://newton.spacedys.com/astdys/index.php?n=588&pc=1.1.6. 
  6. Achillean, achillea (3rd ed.), Oxford University Press, September 2005, http://oed.com/search?searchType=dictionary&q=Achillean%2C+achillea  (Subscription or UK public library membership required.)
  7. 7.0 7.1 7.2 7.3 Grav, T.; Mainzer, A. K.; Bauer, J. M.; Masiero, J. R.; Nugent, C. R. (November 2012). "WISE/NEOWISE Observations of the Jovian Trojan Population: Taxonomy". The Astrophysical Journal 759 (1): 10. doi:10.1088/0004-637X/759/1/49. Bibcode2012ApJ...759...49G.  (online catalog)
  8. 8.0 8.1 8.2 8.3 Usui, Fumihiko; Kuroda, Daisuke; Müller, Thomas G.; Hasegawa, Sunao; Ishiguro, Masateru; Ootsubo, Takafumi et al. (October 2011). "Asteroid Catalog Using Akari: AKARI/IRC Mid-Infrared Asteroid Survey". Publications of the Astronomical Society of Japan 63 (5): 1117–1138. doi:10.1093/pasj/63.5.1117. Bibcode2011PASJ...63.1117U.  (online, AcuA catalog p. 153)
  9. 9.0 9.1 9.2 9.3 Tedesco, E. F.; Noah, P. V.; Noah, M.; Price, S. D. (October 2004). "IRAS Minor Planet Survey V6.0". NASA Planetary Data System – IRAS-A-FPA-3-RDR-IMPS-V6.0: IRAS-A-FPA-3-RDR-IMPS-V6.0. Bibcode2004PDSS...12.....T. https://sbnarchive.psi.edu/pds3/iras/IRAS_A_FPA_3_RDR_IMPS_V6_0/data/diamalb.tab. Retrieved 15 June 2018. 
  10. 10.0 10.1 Shevchenko, V. G.; Krugly, Yu. N.; Belskaya, I. N.; Chiorny, V. G.; Gaftonyuk, N. M.; Slyusarev, I. G. et al. (March 2009). "Do Trojan Asteroids Have the Brightness Opposition Effect?". 40th Lunar and Planetary Science Conference: 1391. Bibcode2009LPI....40.1391S. https://www.lpi.usra.edu/meetings/lpsc2009/pdf/1391.pdf. Retrieved 15 June 2018. 
  11. Shevchenko, V. G.; Belskaya, I. N.; Slyusarev, I. G.; Krugly, Yu. N.; Chiorny, V. G.; Gaftonyuk, N. M. et al. (January 2012). "Opposition effect of Trojan asteroids". Icarus 217 (1): 202–208. doi:10.1016/j.icarus.2011.11.001. Bibcode2012Icar..217..202S. http://adsabs.harvard.edu/cgi-bin/bib_query?bibcode=2012Icar..217..202S. Retrieved 1 January 2016. 
  12. 12.0 12.1 12.2 12.3 12.4 12.5 "LCDB Data for (588) Achilles". Asteroid Lightcurve Database (LCDB). http://www.minorplanet.info/PHP/generateOneAsteroidInfo.php?AstInfo=588%7CAchilles. 
  13. "JPL Small-Body Database Search Engine: orbital class (TJN) and diameter > 50 (km)". JPL's Solar System Dynamics Group. http://ssd.jpl.nasa.gov/sbdb_query.cgi?obj_group=all;obj_kind=all;obj_numbered=all;ast_orbit_class=TJN;OBJ_field=0;ORB_field=0;c1_group=OBJ;c1_item=Ap;c1_op=%3E;c1_value=50;table_format=HTML;max_rows=100;format_option=comp;c_fields=AcBhBgBjBiBnBsAiAp;.cgifields=format_option;.cgifields=ast_orbit_class;.cgifields=table_format;.cgifields=obj_kind;.cgifields=obj_group;.cgifields=obj_numbered;.cgifields=com_orbit_class&query=1&c_sort=ApD. 
  14. 14.0 14.1 Stephens, Robert D. (April 2010). "Trojan Asteroids Observed from GMARS and Santana Observatories: 2009 October - December". The Minor Planet Bulletin 37 (2): 47–48. ISSN 1052-8091. Bibcode2010MPBu...37...47S. http://adsabs.harvard.edu/cgi-bin/bib_query?bibcode=2010MPBu...37...47S. Retrieved 1 January 2016. 
  15. Angeli, C. A.; Lazzaro, D.; Florczak, M. A.; Betzler, A. S.; Carvano, J. M. (May 1999). "A contribution to the study of asteroids with longrotational period". Planetary and Space Science 47 (5): 699–714. doi:10.1016/S0032-0633(98)00122-6. Bibcode1999P&SS...47..699A. http://adsabs.harvard.edu/cgi-bin/bib_query?bibcode=1999P&SS...47..699A. Retrieved 1 January 2016. 
  16. Mottola, Stefano; Di Martino, Mario; Erikson, Anders; Gonano-Beurer, Maria; Carbognani, Albino; Carsenty, Uri et al. (May 2011). "Rotational Properties of Jupiter Trojans. I. Light Curves of 80 Objects". The Astronomical Journal 141 (5): 32. doi:10.1088/0004-6256/141/5/170. Bibcode2011AJ....141..170M. 
  17. Zappala, V.; di Martino, M.; Cellino, A.; de Sanctis, G.; Farinella, P. (December 1989). "Rotational properties of outer belt asteroids". Icarus 82 (2): 354–368.ResearchsupportedbyCNRandMPI. doi:10.1016/0019-1035(89)90043-2. ISSN 0019-1035. Bibcode1989Icar...82..354Z. http://adsabs.harvard.edu/cgi-bin/bib_query?bibcode=1989Icar...82..354Z. Retrieved 1 January 2016. 

External links