10 Hygiea
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 Convex hull model of 10 Hygiea |
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| Discovery | |
|---|---|
| Discovered by: | A. de Gasparis |
| Discovery date: | April 12, 1849 |
| Alternative names: | none |
| Minor planet category: | Main belt (Hygiea family) |
| Orbital characteristics | |
| Epoch July 14, 2004 (JD 2453200.5) | |
| Aphelion distance: | 525.311 Gm (3.511 AU) |
| Perihelion distance: | 413.378 Gm (2.763 AU) |
| Semi-major axis: | 469.345 Gm (3.137 AU) |
| Eccentricity: | 0.119 |
| Orbital period: | 2029.776 d (5.56 a) |
| Avg. orbital speed: | 16.76 km/s |
| Mean anomaly: | 273.788° |
| Inclination: | 3.842° |
| Longitude of ascending node: | 283.646° |
| Argument of perihelion: | 313.557° |
| Physical characteristics | |
| Dimensions: | 500×385×350 km [1][2] |
| Mass: | 8.6 ± 0.7 ×1019 kg [3][4][5] |
| Mean density: | 2.4 g/cm³ |
| Equatorial surface gravity: | 0.091 m/s² |
| Escape velocity: | 0.21 km/s |
| Rotation period: | 1.1510 d [6] |
| Albedo: | 0.072 [1] |
| Temperature: | ~164 K max: 247K (−26° C) [7] |
| Spectral type: | C-type asteroid |
| Absolute magnitude: | 5.43 |
10 Hygiea (IPA: [haɪˈdʒi.ə]) is the fourth largest asteroid, somewhat oblong with diameters of 350–500 km and a mass estimated to be 3% of the total mass of the asteroid belt.
It is the largest of the class of dark C-type asteroids with a carbonaceous surface that are dominant in the outer main belt, which lies beyond the Kirkwood gap at 2.82 AU, and is also the largest body in this region. Its dark surface and larger than average distance from the Sun makes it very dim for such a large asteroid when observed from Earth. In fact it is much dimmer than all the asteroids discovered before it, apart from the unusually small 5 Astraea. This was undoubtedly a factor in its relatively late discovery.
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[edit] Discovery
Hygiea was discovered by Annibale de Gasparis on April 12, 1849 in Naples, Italy. It was his first of many asteroid discoveries. It is named after Hygieia, the Greek goddess of health, daughter of Asclepius (Aesculapius for the Romans).
De Gasparis let the director of the Naples observatory, Ernesto Capocci, name the asteroid to thank him for his encouragement. Capocci chose to call it Igea Borbonica ("Bourbon Hygieia") in honor of the ruling family of the Kingdom of the Two Sicilies where Naples was located. However, by 1852, John Russell Hind would write that "it is universally termed Hygeia, the unnecessary appendage 'Borbonica' being dropped."[8]
The name was often spelled Hygeia in the nineteenth century, for example in the Monthly Notices of the Royal Astronomical Society.
[edit] Characteristics
Hygiea's surface is composed of primitive carbonaceous material similar to the chondrite meteorites. It is the main member of the Hygiea family and contains almost all the mass in this family (well over 90%).The primitive present surface composition would indicate that Hygiea had not been melted during the early period of Solar system formation, in contrast to other large planetesimals like 4 Vesta. Hygiea appears to have a noticeably oblong shape, much more so than the other objects in the "big four" (the dwarf planet Ceres and the asteroids 2 Pallas and 4 Vesta). Aside from being the smallest of the four, another important factor to this end is Hygiea's relatively low density, which is comparable to the icy satellites of Jupiter or Saturn more than to the terrestrial planets or the stony asteroids. It is possible that Hygiea may be classified as a dwarf planet in the future, if it is proven that its shape is due to hydrostatic equilibrium.
Generally Hygiea's properties are the most poorly known out of the "big four" objects in the main belt. It is an unusually slow rotator, taking 27 hours and 37 minutes for a revolution, whereas 6 to 12 hours are more typical for large asteroids. Its direction of rotation is unknown at present, due to a twofold ambiguity in lightcurve data that is exacerbated by its long rotation period, which makes single-night telescope observations span at best only a fraction of a full rotation. Lightcurve analysis indicates that Hygiea's pole points towards either ecliptic coordinates (β, λ) = (30°, 115°) or (30°, 300°) with a 10° uncertainty [2]. This gives an axial tilt of about 60° in both cases.
At least 5 stellar occultations by Hygiea were tracked by Earth-based observers, but all with few observing independent measurements so that much was not learned of its shape. The Hubble Space Telescope was able to resolve the asteroid, and to rule out the presence of any orbiting companions greater than about 16 km in diameter [9].
[edit] References
- ^ a b Supplemental IRAS Minor Planet Survey
- ^ a b M. Kaasalainen et al Models of Twenty Asteroids from Photometric Data, Icarus, Vol. 159, p. 369 (2002).
- ^ S. R. Chesley et al The Mass of Asteroid 10 Hygiea, abstract for American Astronomical Society, DDA meeting #36, #05.05 (2005) (on ADS).
- ^ G. Michalak Determination of asteroid masses, Astronomy & Astrophysics, Vol. 374, 703 (2001).
- ^ Yu. Chernetenko, O. Kochetova, and V. Shor Masses and densities of minor planets Update 1 Sept. 2005. (webpage)
- ^ PDS lightcurve data
- ^ L.F. Lim et al Thermal infrared (8–13 µm) spectra of 29 asteroids: the Cornell Mid-Infrared Asteroid Spectroscopy (MIDAS) Survey, Icarus Vol. 173, p. 385 (2005).
- ^ John Russell Hind, The Solar System, p. 126 (1852). [1]
- ^ A. Storrs et al, Imaging Observations of Asteroids with Hubble Space Telescope, Icarus, Vol. 137, p. 260 (1999).
[edit] External links
- shape model deduced from lightcurve
- A simulation of the orbit of Hygiea
- Yeomans, Donald K.. Horizons system. NASA JPL. Retrieved on 2007-03-20. — Horizons can be used to obtain a current ephemeris.
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For other objects and regions, see Asteroid groups and families, Binary asteroids, Asteroid moons and the Solar System.
For a complete listing, see List of asteroids. See also Pronunciation of asteroid names and Meanings of asteroid names.
