- 6 Hebe
Infobox Planet | discovery=yes | physical_characteristics = yes | bgcolour=#FFFFC0
name=6 Hebe
symbol=
discoverer=Karl Ludwig Hencke
discovered=July 1 ,1847
alt_names=1947 JB
mp_category=Main belt
adjectives=Hebean
epoch=November 26 ,2005 (JD 2453700.5)
semimajor=362.851 Gm (2.426 AU)
perihelion=289.705 Gm (1.937 AU)
aphelion=435.996 Gm (2.914 AU)
eccentricity=0.202
period=1379.756 d (3.78 a)
inclination=14.751°
asc_node=138.752°
arg_peri=239.492°
mean_anomaly=247.947°
avg_speed=18.93 km/s
dimensions=205×185×170 km [http://www.psi.edu/pds/archive/astdata04/simps04/diamalb.tab Supplemental IRAS Minor Planet Survey] ] [http://www.rni.helsinki.fi/~mjk/thirty.pdf J. Torppa et al "Shapes and rotational properties of thirty asteroids from photometric data"] , Icarus, Vol. 164, p. 346 (2003).]
mass=~1.4×1019 kg [http://www.edpsciences.org/articles/aa/pdf/2001/29/aa10228.pdf?access=ok G. Michalak "Determination of asteroid masses"] Astronomy & Astrophysics, Vol. 374, p. 703 (2001).]
density=~4.1 g/cm3
surface_grav=~0.087 m/s2
escape_velocity=~0.13 km/s
rotation=0.3031 d [ [http://www.psi.edu/pds/archive/lc.html Planetary Data System Small Bodies Node, lightcurve parameters] ]
spectral_type=S-type asteroid
magnitude = 7.5cite book | author=Donald H. Menzel and Jay M. Pasachoff | year=1983 | title=A Field Guide to the Stars and Planets | edition=2nd edition | publisher=Houghton Mifflin | pages=p. 391 | location=Boston, MA | isbn=0395348358 ] to 11.50
abs_magnitude=5.71
albedo=0.268 (geometric)
angular_size = 0.26" to 0.065"
single_temperature=~170 K
"max:" ~269 K (-4° C)6 Hebe (pronEng|ˈhiːbi respell|HEE|bee, _gr. "‘Ήβη)" is a large
Main belt asteroid . Hebe is the thirteenth largest asteroid by mass, containing around 0.5 percent of the mass of the entire asteroid belt. Its apparently high bulk density (greater than that of the Earth'sMoon or evenMars ), however, means that by volume it does not rank among the top twenty asteroids. 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 pile s.In brightness, Hebe is the fifth brightest object in the asteroid belt behind Vesta, Ceres, Iris and Pallas. It has a mean opposition magnitude of +8.3, about equal to the mean brightness of Titan [ [http://jas.org.jo/ast.html The Brightest Asteroids] ] and can reach +7.5 at an opposition near perihelion.
Hebe is probably the parent body of the
H chondrite meteorites, which account for a remarkable 40% of allmeteorite s striking the Earth.Discovery
Hebe was the sixth
asteroid to be discovered, onJuly 1 ,1847 byKarl Ludwig Hencke . It was the second and final asteroid discovery by Hencke, who had previously found5 Astraea . The name "Hebe" was proposed byCarl Friedrich Gauss .Major meteorite source
6 Hebe is the probable parent body of the
H chondrite meteorite s and theIIE iron meteorite s. Remarkably, this would imply that it is the source of about 40% of all meteorites striking the Earth. Evidence for this connection includes the following (afterMichael Gaffey andSarah L. Gilbert . [http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998M%26PS...33.1281G&db_key=AST&data_type=HTML&format=&high=438c93072f28336 M. J. Gaffey & S. L. Gilbert "Asteroid 6 Hebe: The probable parent body of the H-Type ordinary chondrites and the IIE iron metorites"] , Meteoritics & Planetary Science, Vol. 33, p. 1281 (1998).] ):
* The spectrum of Hebe matches a mix of 60% H chondrite and 40% IIE iron meteorite material.
* The IIE type are unusual among the iron meteorites, and probably formed from impact melt, rather than being fragments of the core of a differentiated asteroid.
* The IIE irons and H chondrites likely come from the same parent body, due to similar trace mineral and oxygenisotope ratios.
* Asteroids with spectra similar to theordinary chondrite meteorites (accounting for 85% of all falls, including the H chondrites) are extremely rare.
* 6 Hebe is extremely well placed to send impact debris to Earth-crossing orbits. Ejecta with even relatively small velocities (~280 m/s) can enter the chaotic regions of the 3:1Kirkwood gap at 2.50 AU and the nearby u_6,!secular resonance which determines the high-inclination edge of themain belt at about 16°inclinations hereabouts.
* Of the asteroids in this "well-placed" orbit, Hebe is the largest.
* An analysis of likely contributors to the Earth's meteorite flux places 6 Hebe at the top of the list, [http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1994A%26A...282..955M&data_type=PDF_HIGH&type=PRINTER&filetype=.pdf A. Morbidelli et al "Delivery of meteorites through the ν6 secular resonance"] , Astronomy & Astrophysics, Vol. 282, p. 955 (1994).] due to its position and relatively large size. "If Hebe is not the H-chondrite parent body, then where are the meteorites from Hebe?"Physical characteristics
Lightcurve analysis suggests that Hebe has a rather angular shape, which may be due to several large impact craters. Hebe rotates in a prograde direction, with the north pole pointing towards ecliptic coordinates (β, λ) = (45°, 339°) with a 10° uncertainty. This gives an
axial tilt of 42°.It has a bright surface and, if its identification as the parent body of the H chondrites is correct, asurface composition of
silicate chondritic rocks mixed with pieces ofnickel -iron metal . A likely scenario for the formation of the surface metal is as follows:
# Large impacts caused local melting of the iron rich H chondrite surface. The metals, being heavier, would have settled to the bottom of the magma lake, forming a metallic layer buried by a relatively shallow layer of silicates.
# Later sizeable impacts broke up and mixed these layers.
# Small frequent impacts tend to preferentially pulverize the weaker rocky debris, leading to an increased concentration of the larger metal fragments at the surface, such that they eventually comprise ~40% of the immediate surface at the present time.Moon
On
March 5 ,1977 Hebe occulted Kaffaljidhma (γ Ceti), a moderately bright 3rd magnitudestar . No other observed occultations by Hebe have been reported.As a result of that occultation, a small Hebean moon was reported by
Paul D. Maley . [ [http://www.johnstonsarchive.net/astro/asteroidmoonsq.html W. R. Johnston "Other reports of Asteroid/TNO Companions] ] It was nicknamed "Jebe" (seeHeebie Jeebies ). However, the discovery has not been confirmed.References
* — Horizons can be used to obtain a current ephemeris
External links
* [http://www.rni.helsinki.fi/~mjk/thirty.pdf shape model deduced from lightcurve]
* [http://adsabs.harvard.edu//full/seri/MNRAS/0007//0000283.000.html MNRAS 7 (1847) 283] (discovery announcement)
* [http://adsabs.harvard.edu//full/seri/MNRAS/0008//0000104.000.html MNRAS 8 (1848) 103]
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