6 Hebe

6 Hebe

A three-dimensional model of 6 Hebe based on its light curve
Discovery
Discovered by Karl Ludwig Hencke
Discovery date July 1, 1847
Designations
Pronunciation /ˈhiːbiː/ HEE-bee
Named after
 Hēbē
1947 JB
Main belt
Adjectives Hebean
Orbital characteristics
Epoch November 26, 2005 (JD 2453700.5)
Aphelion 2.914 AU (435.996 Gm)
Perihelion 1.937 AU (289.705 Gm)
2.426 AU (362.851 Gm)
Eccentricity 0.202
3.78 a (1379.756 d)
18.93 km/s
247.947°
Inclination 14.751°
138.752°
239.492°
Proper orbital elements[1]
2.4252710 AU
0.1584864
14.3511092°
95.303184 deg / yr
3.77742 yr
(1379.702 d)
Precession of perihelion
 31.568209 arcsec / yr
Precession of the ascending node
 −41.829042 arcsec / yr
Physical characteristics
Dimensions 205×185×170 km[2][3][4]
186 km (mean)
109 000 km2[5]
Volume 3 380 000 km3[5]
Mass 1.28×1019 kg[2]
Mean density
 3.81±0.26 g/cm³[2]
~0.087 m/s2
~0.13 km/s
0.3031 d[6]
Equatorial rotation velocity
 22.4 m/s[5]
Albedo 0.268 (geometric)[3]
Temperature ~170 K
max: ~269 K (−4°C)
Spectral type
 S-type asteroid
7.5[7] to 11.50
5.71
0.26" to 0.065"

    6 Hebe (/ˈhiːbiː/ HEE-bee) is a large main-belt asteroid, containing around half a percent of the mass of the belt. However, due to its apparently high bulk density (greater than that of the Moon or even Mars), 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 bound rubble piles.

    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,[8] and can reach +7.5 at an opposition near perihelion.

    Hebe is probably the parent body of the H chondrite meteorites, which account for about 40% of all meteorites striking Earth.

    History

    Hebe was discovered on 1 July 1847 by Karl Ludwig Hencke, the sixth asteroid discovered. It was the second and final asteroid discovery by Hencke, after 5 Astraea. The name Hebe, goddess of youth, was proposed by Carl Friedrich Gauss.

    Major meteorite source

    Hebe is the probable parent body of the H chondrite meteorites and the IIE iron meteorites. This would imply that it is the source of about 40% of all meteorites striking Earth. Evidence for this connection includes the following:

    Physical characteristics

    Size comparison: the first 10 asteroids profiled against the Moon. Hebe is sixth from the left.

    Lightcurve analysis suggests that Hebe has a rather angular shape, which may be due to several large impact craters.[4] Hebe rotates in a prograde direction, with the north pole pointing towards ecliptic coordinates (β, λ) = (45°, 339°) with a 10° uncertainty.[4] 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, a surface composition of silicate chondritic rocks mixed with pieces of iron–nickel. A likely scenario for the formation of the surface metal is as follows:

    1. 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.
    2. Later sizeable impacts broke up and mixed these layers.
    3. 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.

    Orbit

    The orbit of 6 Hebe compared with the orbits of Earth, Mars and Jupiter

    Moon

    On March 5, 1977 Hebe occulted Kaffaljidhma (γ Ceti), a moderately bright 3rd-magnitude star. No other observed occultations by Hebe have been reported.

    As a result of that occultation, a small moon around Hebe was reported by Paul D. Maley.[11] It was nicknamed "Jebe" (see Heebie-jeebies). This is the first modern-day suggestion that asteroids have satellites. It was 17 years later when the first asteroid moon was formally discovered (Dactyl, the satellite of 243 Ida). However, the discovery of Hebe's moon has not been confirmed.

    See also

    References

    1. ↑ "AstDyS-2 Hebe Synthetic Proper Orbital Elements". Department of Mathematics, University of Pisa, Italy. Retrieved 2011-10-01.
    2. 1 2 3 Jim Baer (2008). "Recent Asteroid Mass Determinations". Personal Website. Retrieved 2008-11-28.
    3. 1 2 Supplemental IRAS Minor Planet Survey
    4. 1 2 3 J. Torppa et al. Shapes and rotational properties of thirty asteroids from photometric data, Icarus, Vol. 164, p. 346 (2003).
    5. 1 2 3 Calculated based on the known parameters
    6. ↑ Planetary Data System Small Bodies Node, lightcurve parameters
    7. ↑ Donald H. Menzel & Jay M. Pasachoff (1983). A Field Guide to the Stars and Planets (2nd ed.). Boston, MA: Houghton Mifflin. p. 391. ISBN 0-395-34835-8.
    8. ↑ The Brightest Asteroids
    9. ↑ A. Morbidelli et al. Delivery of meteorites through the ν6 secular resonance, Astronomy & Astrophysics, Vol. 282, p. 955 (1994).
    10. ↑ M. J. Gaffey & S. L. Gilbert Asteroid 6 Hebe: The probable parent body of the H-Type ordinary chondrites and the IIE iron meteorites, Meteoritics & Planetary Science, Vol. 33, p. 1281 (1998).
    11. ↑ W. R. Johnston Other reports of Asteroid/TNO Companions

    External links

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