6 Hebe (/ˈhiːbiː/) is a largemain-beltasteroid, containing around 0.5% of the mass of the belt. However, due to its apparently high bulk density (greater than that of theMoon), Hebe does not rank among the top twenty asteroids by volume. This high bulk density suggests an extremely solid body that has not been impacted by collisions, which is not typical of asteroids of its size – they tend to be loosely-boundrubble piles.
Inbrightness, Hebe is the fifth-brightest object in the asteroid belt afterVesta,Ceres,Iris, andPallas. It has a mean opposition magnitude of +8.3, about equal to the mean brightness of Saturn's moonTitan,[10] and can reach +7.5 at an opposition near perihelion.
Hebe may be the parent body of theH chondrite meteorites, which account for about 40% of allmeteorites striking Earth.
Hebe was discovered on 1 July 1847 by German astronomerKarl Ludwig Hencke in the town of Driesen,Brandenburg,Prussia (nowDrezdenko,Poland).[1] It is the sixthasteroid discovered. It was the second and final asteroid discovery by Hencke, after5 Astraea. The nameHebe, after theGreek goddess of youth, was proposed byCarl Friedrich Gauss at Hencke's request.[11] The first asteroids discovered had widely been consideredplanets by astronomers, but the rapid discoveries of several new asteroids in the late 1840s complicated the classification of asteroids.[12] In the years following its discovery, Hebe was variously labelled as a planet,[11] small planet, or asteroid.[13] Eventually, throughout the latter half of the 19th century, the terms "asteroid" and "minor planet" became favored,[12] although some astronomers continued referring to Hebe as a planet in this period.[14]
Gauss chose a wineglass as Hebe'sastronomical symbol.[11][15] It was encoded inUnicode 17.0 as U+1CEC0 ().[16][17] As asteroids and their symbols grew in number, the practicality of assigning unique astronomical symbols to each asteroid was questioned. In 1851, astronomerJohann Franz Encke proposed a simpler system of a number—denoting the order of discovery—inscribed in a circle. For Hebe, this would be ⑥.[12][18]: 80 This system was widely adopted by astronomers, though astronomers eventually switched to using parentheses enclosing the number—thus(6) Hebe[19] or6 Hebe[1] in modern notation.[12]
Hebe resides near but does not participate in severalorbital resonances. It orbits close to the 3:1mean-motion resonance (MMR) withJupiter at approximately 2.50 AU.[21]: 1282 Asteroids caught in the 3:1 Jovian MMR have orbital periods one-third that of Jupiter's; their orbits are destabilized and they are eventually removed by encounters with the planets, creating the 3:1 Kirkwood gap.[22]: 101 Hebe is also located near the destabilizing ()secular resonance withSaturn, which at Hebe's average distance of 2.426 AU is located at 15–16° inclination.[21]: 1282
In the 1990s, Hebe was identified as a possible source forH chondrites andIIE iron meteorites.[21]: 1293 [23]: 3 Its location near the 3:1 Jovian MMR and the Saturnian secular resonance means that fragments created byimpact events are easily destabilized into Earth-crossing orbits, where they could eventually impact Earth as meteorites.[24]: 288, 300 Indeed, the H chondritic surface compositions of twonear-Earth objects—(4953) 1990 MU and 2007 LE—point towards Hebe as their parent body.[25]: 65 [26]: 436 Spectral observations of asteroids near the 3:1 Kirkwood gap in the early 2010s identified695 Bella,1166 Sakuntala, and1607 Mavis as potential relatives of Hebe.[27]: 531–532 [28] However, they are located on the opposite side of the 3:1 Kirkwood gap, indicating that they jumped across the gap.[23]: 3–4 In 2020, a study led by Sherry K. Fieber-Beyer identified nine additional candidate members of the tentative Hebe family, with some located on Hebe's side of the 3:1 Kirkwood gap.[23]: 1
Simulations (top) and direct images (bottom) of 6 Hebe[29]Size comparison: the first 10 asteroids profiled against theMoon. Hebe is sixth from the left.
Hebe is a large asteroid, with a volume-equivalentspheroidal diameter of 193 ± 6 kilometres (119.9 ± 3.7 mi). Though Hebe's shape approximates an oblate spheroid, it hosts numerous extreme topographical features. Five large depressions have been identified on its surface, possibly representing deepimpact craters.[30]: 4–6 The depressions range from around 50 km (31 mi) to over 100 km (62 mi) in size, with depths between 7 and 18 kilometres (4.3 and 11.2 mi).[30]: 6 Hebe additionally has a large, flattened face, giving it the appearance of a "lopped-off tooth". This large facet may represent a section of the asteroid that was blasted away into space by an ancientimpact event.[23]: 9
Based on Hebe'slightcurve, or variations in its observed brightness, it rotates in aprograde (counterclockwise) direction with a rotation period of 7.27 hours. Its north pole pointing towardsecliptic coordinates (β, λ) = (45°, 339°) with a 10° uncertainty.[6]: 349
Hebe is classified as anS-type asteroid[31]: 104 under theTholen classification scheme.[32] Planetary scientistMichael James Gaffey further subdivided S-type asteroids into seven mineralogical subclasses,[33] categorizing Hebe as an S(IV)-type asteroid. Hebe's S(IV) classification indicates its surface is silicate (or stony) in composition andundifferentiated or partially differentiated.[21]: 1282
^Gould, B. A., Jr. (July 1848). "On the Orbits of the Asteroids".American Journal of Science and Arts.6 (16).{{cite journal}}: CS1 maint: multiple names: authors list (link)
^Steger, Franz (1847).Ergänzungs-conversationslexikon [Supplementary Conversational Lexicon] (in German). Vol. 3. p. 442.Hofrath Gauß gab auf Hencke's Ansuchen diesem neuen Planetoiden den Namen Hebe mit dem Zeichen (ein Weinglas).
^Farinella, Paolo; Froeschle, Christiane; Gonczi, Robert (March 1993). "Meteorites from the Asteroid 6 Hebe".Celestial Mechanics and Dynamical Astronomy.56 (1–2):287–305.Bibcode:1993CeMDA..56..287F.doi:10.1007/BF00699740.
^Kelley, Michael S.; Gaffey, Michael J.; Reddy, Vishnu; Sanchez, Juan A. (May 2014). "Surface composition of near-Earth Asteroid (4953) 1990 MU: Possible fragment of (6) Hebe".Icarus.233:61–65.Bibcode:2014Icar..233...61K.doi:10.1016/j.icarus.2014.01.015.
^Fieber-Beyer, Sherry K.; Gaffey, Michael J.; Bottke, William F.; Hardersen, Paul S. (April 2015). "Potentially hazardous Asteroid 2007 LE: Compositional link to the black chondrite Rose City and Asteroid (6) Hebe".Icarus.250:430–437.Bibcode:2015Icar..250..430F.doi:10.1016/j.icarus.2014.12.021.
^Fieber-Beyer, Sherry K.; Gaffey, Michael J.; Kelley, Michael S.; Reddy, Vishnu; Reynolds, Chalbeth M.; Hicks, Tony (June 2011). "The Maria asteroid family: Genetic relationships and a plausible source of mesosiderites near the 3:1 Kirkwood Gap".Icarus.213 (2):524–537.Bibcode:2011Icar..213..524F.doi:10.1016/j.icarus.2011.03.009.
^Gaffey, M. J.; Fieber-Beyer, S. K. (September 2013).Identification of a Possible H-Chondrite Asteroid Family. 76th Annual Meeting of the Meteoritical Society. Edmonton, Alberta, Canada.Bibcode:2013M&PSA..76.5124G.
^abMarsset, M.; Carry, B.; Dumas, C.; Hanuš, J.; Viikinkoski, M.; Vernazza, P.; Müller, T. G.; Delbo, M.; Jehin, E.; Gillom, M.; Grice, J.; Yang, B.; Fusco, T.; Berthier, J.; Sonnett, S.; Kugel, F.; Caron, J.; Behrend, R. (August 2017). "3D shape of asteroid (6) Hebe from VLT/SPHERE imaging: Implications for the origin of ordinary H chondrites".Astronomy & Astrophysics.604: A64.arXiv:1705.10515.Bibcode:2017A&A...604A..64M.doi:10.1051/0004-6361/201731021. A64.
^Migliorini, F.; Manara, A.; Scaltriti, F.; Farinella, P.; Cellino, A.; Di Martino, M. (July 1997). "Surface Properties of (6) Hebe: A Possible Parent Body of Ordinary Chondrites".Icarus.128 (1):104–113.Bibcode:1997Icar..128..104M.doi:10.1006/icar.1997.5679.
^Gaffey, Michael J.; Bell, Jeffrey F.; Brown, R. Hamilton; Burbine, Thomas H.; Piatek, Jennifer L.; Reed, Kevin L.; Chaky, Damon A. (December 1993). "Mineralogic variations within the S-type asteroid class".Icarus.106 (2):573–602.Bibcode:1993Icar..106..573G.doi:10.1006/icar.1993.1194.
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