* Astronomy

Asteroid (6) Hebe at magnitude +9.2 is currently passing close to the magnitude +9.50 Globular cluster NGC 6366 in the constellation Ophiuchus

Title: 3D shape of asteroid (6) Hebe from VLT/SPHERE imaging: Implications for the origin of ordinary H chondrites
Author: M. Marsset, B. Carry, C. Dumas, J. Hanus, M. Viikinkoski, P. Vernazza, T. G. Müller, M. Delbo, E. Jehin, M. Gillon, J. Grice, B. Yang, T. Fusco, J. Berthier, S. Sonnett, F. Kugel, J. Caron, R. Behrend

Context. The high-angular-resolution capability of the new-generation ground-based adaptive-optics camera SPHERE at ESO VLT allows us to assess, for the very first time, the cratering record of medium-sized (D~100-200 km) asteroids from the ground, opening the prospect of a new era of investigation of the asteroid belt's collisional history.
Aims. We investigate here the collisional history of asteroid (6) Hebe and challenge the idea that Hebe may be the parent body of ordinary H chondrites, the most common type of meteorites found on Earth (~34% of the falls).
Methods. We observed Hebe with SPHERE as part of the science verification of the instrument. Combined with earlier adaptive-optics images and optical light curves, we model the spin and three-dimensional (3D) shape of Hebe and check the consistency of the derived model against available stellar occultations and thermal measurements.
Results. Our 3D shape model fits the images with sub-pixel residuals and the light curves to 0.02 mag. The rotation period (7.274 47 h), spin (343 deg,+47 deg), and volume-equivalent diameter (193 ± 6km) are consistent with previous determinations and thermophysical modelling. Hebe's inferred density is 3.48 ± 0.64 g.cm-3 , in agreement with an intact interior based on its H-chondrite composition. Using the 3D shape model to derive the volume of the largest depression (likely impact crater), it appears that the latter is significantly smaller than the total volume of close-by S-type H-chondrite-like asteroid families.
Conclusions. Our results imply that (6) Hebe is not the most likely source of H chondrites. Over the coming years, our team will collect similar high-precision shape measurements with VLT/SPHERE for ~40 asteroids covering the main compositional classes, thus providing an unprecedented dataset to investigate the origin and collisional evolution of the asteroid belt.

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Asteroid (6) Hebe is at Opposition in the constellation Eridani on the 15th November 2014.

Magnitude: 8.1
Distance to Earth: 1.070 AU
Distance to Sun: 1.997 AU

Asteroid (6) Hebe was discovered by Karl Henckein on the 1st July 1847

In brightness, Hebe is the fifth brightest object in the asteroid belt after Vesta, Ceres, Iris and Pallas. It has a mean opposition magnitude of +8.3, about equal to the mean brightness of Titan[7] and can reach +7.5 at an opposition near perihelion.
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Ephemeris

Date    TT    R. A. (2000) Decl.     Delta      r     Elong.  Phase     V
2014 08 08    03 07 05.0 +02 47 20   1.6500  1.9377    90.1    31.6     9.4
2014 08 09    03 08 46.7 +02 45 08   1.6405  1.9375    90.6    31.5     9.4
2014 08 10    03 10 27.5 +02 42 47   1.6310  1.9374    91.1    31.5     9.4
2014 08 11    03 12 07.4 +02 40 14   1.6216  1.9373    91.7    31.5     9.4
2014 08 12    03 13 46.6 +02 37 31   1.6122  1.9371    92.2    31.5     9.4
2014 08 13    03 15 24.8 +02 34 37   1.6028  1.9370    92.8    31.5     9.4
2014 08 14    03 17 02.2 +02 31 33   1.5934  1.9369    93.3    31.5     9.4
2014 08 15    03 18 38.6 +02 28 17   1.5841  1.9369    93.9    31.4     9.3
2014 08 16    03 20 14.1 +02 24 51   1.5748  1.9368    94.4    31.4     9.3
2014 08 17    03 21 48.6 +02 21 14   1.5655  1.9368    95.0    31.4     9.3
2014 08 18    03 23 22.1 +02 17 26   1.5563  1.9368    95.5    31.3     9.3
2014 08 19    03 24 54.6 +02 13 27   1.5471  1.9367    96.1    31.3     9.3
2014 08 20    03 26 26.1 +02 09 18   1.5379  1.9368    96.7    31.3     9.3
2014 08 21    03 27 56.4 +02 04 57   1.5288  1.9368    97.2    31.2     9.3
2014 08 22    03 29 25.7 +02 00 26   1.5197  1.9368    97.8    31.2     9.2
2014 08 23    03 30 53.8 +01 55 44   1.5106  1.9369    98.4    31.1     9.2
2014 08 24    03 32 20.8 +01 50 51   1.5016  1.9369    99.0    31.0     9.2
2014 08 25    03 33 46.5 +01 45 48   1.4926  1.9370    99.6    31.0     9.2
2014 08 26    03 35 11.1 +01 40 33   1.4837  1.9371   100.2    30.9     9.2
2014 08 27    03 36 34.4 +01 35 09   1.4748  1.9372   100.8    30.8     9.2
2014 08 28    03 37 56.5 +01 29 33   1.4659  1.9374   101.4    30.7     9.2
2014 08 29    03 39 17.3 +01 23 47   1.4571  1.9375   102.0    30.7     9.1
2014 08 30    03 40 36.7 +01 17 51   1.4483  1.9377   102.6    30.6     9.1
2014 08 31    03 41 54.9 +01 11 44   1.4396  1.9379   103.2    30.5     9.1
2014 09 01    03 43 11.6 +01 05 28   1.4309  1.9381   103.8    30.4     9.1
2014 09 02    03 44 27.0 +00 59 01   1.4223  1.9383   104.4    30.3     9.1
2014 09 03    03 45 41.0 +00 52 24   1.4138  1.9385   105.1    30.2     9.1
2014 09 04    03 46 53.5 +00 45 37   1.4052  1.9388   105.7    30.1     9.1
2014 09 05    03 48 04.5 +00 38 40   1.3968  1.9390   106.3    29.9     9.0
2014 09 06    03 49 14.1 +00 31 34   1.3884  1.9393   107.0    29.8     9.0
2014 09 07    03 50 22.2 +00 24 18   1.3801  1.9396   107.6    29.7     9.0
2014 09 08    03 51 28.7 +00 16 53   1.3718  1.9399   108.3    29.6     9.0
2014 09 09    03 52 33.7 +00 09 18   1.3636  1.9402   108.9    29.4     9.0
2014 09 10    03 53 37.1 +00 01 34   1.3554  1.9406   109.6    29.3     9.0
2014 09 11    03 54 38.8 -00 06 19   1.3473  1.9409   110.2    29.1     8.9
2014 09 12    03 55 38.9 -00 14 21   1.3393  1.9413   110.9    29.0     8.9
2014 09 13    03 56 37.3 -00 22 31   1.3313  1.9417   111.6    28.8     8.9
2014 09 14    03 57 34.0 -00 30 50   1.3234  1.9421   112.2    28.7     8.9
2014 09 15    03 58 29.0 -00 39 18   1.3156  1.9425   112.9    28.5     8.9
2014 09 16    03 59 22.2 -00 47 53   1.3079  1.9429   113.6    28.3     8.9
2014 09 17    04 00 13.5 -00 56 37   1.3002  1.9434   114.3    28.1     8.8
2014 09 18    04 01 03.0 -01 05 28   1.2926  1.9438   115.0    27.9     8.8
2014 09 19    04 01 50.7 -01 14 26   1.2851  1.9443   115.7    27.8     8.8
2014 09 20    04 02 36.4 -01 23 32   1.2776  1.9448   116.4    27.6     8.8
2014 09 21    04 03 20.2 -01 32 44   1.2703  1.9453   117.1    27.4     8.8
2014 09 22    04 04 02.1 -01 42 03   1.2630  1.9459   117.8    27.1     8.7
2014 09 23    04 04 41.9 -01 51 29   1.2558  1.9464   118.5    26.9     8.7
2014 09 24    04 05 19.8 -02 01 00   1.2487  1.9470   119.3    26.7     8.7
2014 09 25    04 05 55.7 -02 10 36   1.2417  1.9475   120.0    26.5     8.7
2014 09 26    04 06 29.4 -02 20 18   1.2348  1.9481   120.7    26.3     8.7
2014 09 27    04 07 01.2 -02 30 04   1.2280  1.9487   121.4    26.0     8.7
2014 09 28    04 07 30.8 -02 39 55   1.2213  1.9493   122.2    25.8     8.6
2014 09 29    04 07 58.3 -02 49 50   1.2147  1.9500   122.9    25.5     8.6
2014 09 30    04 08 23.7 -02 59 48   1.2082  1.9506   123.7    25.3     8.6
2014 10 01    04 08 46.9 -03 09 49   1.2018  1.9513   124.4    25.0     8.6
2014 10 02    04 09 08.0 -03 19 53   1.1956  1.9519   125.2    24.8     8.6
2014 10 03    04 09 27.0 -03 29 59   1.1894  1.9526   125.9    24.5     8.6
2014 10 04    04 09 43.7 -03 40 06   1.1834  1.9533   126.7    24.3     8.5
2014 10 05    04 09 58.3 -03 50 14   1.1774  1.9541   127.4    24.0     8.5
2014 10 06    04 10 10.7 -04 00 23   1.1716  1.9548   128.2    23.7     8.5
2014 10 07    04 10 20.9 -04 10 33   1.1659  1.9556   129.0    23.4     8.5
2014 10 08    04 10 28.8 -04 20 41   1.1604  1.9563   129.7    23.1     8.5
2014 10 09    04 10 34.6 -04 30 49   1.1549  1.9571   130.5    22.8     8.5
2014 10 10    04 10 38.1 -04 40 55   1.1496  1.9579   131.3    22.5     8.4
2014 10 11    04 10 39.4 -04 51 00   1.1445  1.9587   132.0    22.3     8.4
2014 10 12    04 10 38.5 -05 01 01   1.1394  1.9595   132.8    22.0     8.4
2014 10 13    04 10 35.3 -05 10 59   1.1346  1.9604   133.6    21.6     8.4
2014 10 14    04 10 29.9 -05 20 53   1.1298  1.9612   134.3    21.3     8.4
2014 10 15    04 10 22.3 -05 30 43   1.1252  1.9621   135.1    21.0     8.3
2014 10 16    04 10 12.4 -05 40 27   1.1207  1.9630   135.8    20.7     8.3
2014 10 17    04 10 00.3 -05 50 06   1.1164  1.9639   136.6    20.4     8.3
2014 10 18    04 09 46.1 -05 59 37   1.1123  1.9648   137.3    20.1     8.3
2014 10 19    04 09 29.6 -06 09 01   1.1083  1.9657   138.1    19.8     8.3
2014 10 20    04 09 11.0 -06 18 17   1.1044  1.9666   138.8    19.5     8.3
2014 10 21    04 08 50.3 -06 27 24   1.1007  1.9676   139.6    19.2     8.3
2014 10 22    04 08 27.5 -06 36 22   1.0972  1.9686   140.3    18.8     8.2
2014 10 23    04 08 02.6 -06 45 09   1.0939  1.9695   141.0    18.5     8.2
2014 10 24    04 07 35.6 -06 53 44   1.0907  1.9705   141.7    18.2     8.2
2014 10 25    04 07 06.7 -07 02 08   1.0877  1.9715   142.4    17.9     8.2
2014 10 26    04 06 35.9 -07 10 19   1.0849  1.9726   143.1    17.6     8.2
2014 10 27    04 06 03.2 -07 18 17   1.0823  1.9736   143.8    17.3     8.2
2014 10 28    04 05 28.6 -07 26 01   1.0798  1.9746   144.4    17.0     8.2
2014 10 29    04 04 52.3 -07 33 29   1.0775  1.9757   145.1    16.7     8.1
2014 10 30    04 04 14.3 -07 40 42   1.0755  1.9768   145.7    16.5     8.1
2014 10 31    04 03 34.6 -07 47 39   1.0736  1.9779   146.3    16.2     8.1
2014 11 01    04 02 53.3 -07 54 19   1.0719  1.9790   146.9    15.9     8.1
2014 11 02    04 02 10.6 -08 00 41   1.0703  1.9801   147.4    15.7     8.1
2014 11 03    04 01 26.4 -08 06 45   1.0690  1.9812   148.0    15.4     8.1
2014 11 04    04 00 40.8 -08 12 30   1.0679  1.9824   148.5    15.2     8.1
2014 11 05    03 59 53.9 -08 17 56   1.0670  1.9835   148.9    15.0     8.1
2014 11 06    03 59 05.9 -08 23 02   1.0663  1.9847   149.4    14.7     8.1
2014 11 07    03 58 16.6 -08 27 48   1.0657  1.9859   149.8    14.5     8.1
2014 11 08    03 57 26.4 -08 32 12   1.0654  1.9871   150.2    14.4     8.1
2014 11 09    03 56 35.1 -08 36 15   1.0653  1.9883   150.5    14.2     8.1
2014 11 10    03 55 43.0 -08 39 56   1.0654  1.9895   150.8    14.1     8.1
2014 11 11    03 54 50.0 -08 43 15   1.0657  1.9907   151.1    13.9     8.1
2014 11 12    03 53 56.3 -08 46 11   1.0662  1.9920   151.3    13.8     8.0
2014 11 13    03 53 02.0 -08 48 44   1.0669  1.9932   151.5    13.7     8.0
2014 11 14    03 52 07.2 -08 50 54   1.0678  1.9945   151.6    13.7     8.0
2014 11 15    03 51 11.9 -08 52 40   1.0689  1.9958   151.7    13.6     8.1
2014 11 16    03 50 16.2 -08 54 01   1.0703  1.9971   151.7    13.6     8.1
2014 11 17    03 49 20.3 -08 54 59   1.0718  1.9984   151.7    13.6     8.1
2014 11 18    03 48 24.2 -08 55 32   1.0736  1.9997   151.7    13.6     8.1
2014 11 19    03 47 28.1 -08 55 40   1.0755  2.0010   151.6    13.6     8.1
2014 11 20    03 46 32.1 -08 55 24   1.0777  2.0024   151.5    13.6     8.1
2014 11 21    03 45 36.1 -08 54 42   1.0801  2.0037   151.3    13.7     8.1
2014 11 22    03 44 40.5 -08 53 36   1.0827  2.0051   151.1    13.8     8.1
2014 11 23    03 43 45.1 -08 52 05   1.0856  2.0065   150.8    13.9     8.1
2014 11 24    03 42 50.2 -08 50 10   1.0886  2.0078   150.5    14.0     8.1
2014 11 25    03 41 55.9 -08 47 49   1.0919  2.0093   150.2    14.1     8.1
2014 11 26    03 41 02.1 -08 45 04   1.0953  2.0107   149.8    14.3     8.1
2014 11 27    03 40 09.1 -08 41 55   1.0990  2.0121   149.4    14.5     8.2
2014 11 28    03 39 16.9 -08 38 22   1.1029  2.0135   148.9    14.6     8.2
2014 11 29    03 38 25.6 -08 34 25   1.1070  2.0150   148.5    14.8     8.2
2014 11 30    03 37 35.2 -08 30 04   1.1112  2.0164   148.0    15.0     8.2
2014 12 01    03 36 45.9 -08 25 21   1.1157  2.0179   147.4    15.3     8.2
2014 12 02    03 35 57.7 -08 20 15   1.1204  2.0194   146.9    15.5     8.2
2014 12 03    03 35 10.7 -08 14 46   1.1253  2.0209   146.3    15.7     8.3
2014 12 04    03 34 24.9 -08 08 56   1.1304  2.0224   145.7    15.9     8.3
2014 12 05    03 33 40.5 -08 02 44   1.1357  2.0239   145.1    16.2     8.3
2014 12 06    03 32 57.4 -07 56 11   1.1412  2.0254   144.4    16.4     8.3
2014 12 07    03 32 15.7 -07 49 18   1.1469  2.0270   143.8    16.7     8.3
2014 12 08    03 31 35.5 -07 42 05   1.1527  2.0285   143.1    17.0     8.4
2014 12 09    03 30 56.8 -07 34 32   1.1588  2.0301   142.4    17.2     8.4
2014 12 10    03 30 19.7 -07 26 40   1.1650  2.0316   141.7    17.5     8.4
2014 12 11    03 29 44.2 -07 18 30   1.1714  2.0332   141.0    17.8     8.4
2014 12 12    03 29 10.3 -07 10 01   1.1780  2.0348   140.2    18.0     8.4
2014 12 13    03 28 38.1 -07 01 15   1.1848  2.0364   139.5    18.3     8.5
2014 12 14    03 28 07.7 -06 52 12   1.1918  2.0380   138.7    18.6     8.5
2014 12 15    03 27 38.9 -06 42 53   1.1989  2.0396   138.0    18.8     8.5
2014 12 16    03 27 12.0 -06 33 18   1.2063  2.0412   137.2    19.1     8.5
2014 12 17    03 26 46.9 -06 23 28   1.2138  2.0429   136.5    19.4     8.6
2014 12 18    03 26 23.6 -06 13 22   1.2214  2.0445   135.7    19.6     8.6
2014 12 19    03 26 02.2 -06 03 03   1.2292  2.0462   134.9    19.9     8.6
2014 12 20    03 25 42.7 -05 52 30   1.2372  2.0479   134.1    20.2     8.6
2014 12 21    03 25 25.0 -05 41 43   1.2454  2.0495   133.3    20.4     8.6
2014 12 22    03 25 09.3 -05 30 44   1.2537  2.0512   132.5    20.7     8.7
2014 12 23    03 24 55.5 -05 19 33   1.2622  2.0529   131.8    20.9     8.7
2014 12 24    03 24 43.7 -05 08 11   1.2708  2.0546   131.0    21.2     8.7
2014 12 25    03 24 33.8 -04 56 37   1.2796  2.0563   130.2    21.4     8.7
2014 12 26    03 24 25.8 -04 44 54   1.2885  2.0581   129.4    21.7     8.8
2014 12 27    03 24 19.8 -04 33 00   1.2976  2.0598   128.6    21.9     8.8
2014 12 28    03 24 15.8 -04 20 57   1.3068  2.0615   127.8    22.1     8.8
2014 12 29    03 24 13.7 -04 08 46   1.3161  2.0633   127.0    22.4     8.8
2014 12 30    03 24 13.5 -03 56 26   1.3256  2.0651   126.2    22.6     8.9
2014 12 31    03 24 15.3 -03 43 58   1.3352  2.0668   125.4    22.8     8.9