10 Hygiea
Encyclopedia : 1 : 10 : 10H : 10 Hygiea
| Orbital elements | |
|---|---|
| Eccentricity (orbit)>e | |
| Inclination>i | ° |
| Perihelion>q |
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| Argument of perihelion>ω | ° |
| Semi-major axis>a | AU |
| Longitude of the ascending node>ω | ° |
| Aphelion>Q |
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| Mean anomaly>M | ° |
| Orbital period>P | years |
| Mean motion>n | °/day |
| Time of perihelion passage>TP | |
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.
Discovery
Hygiea was discovered by A. 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). Curiously, note the spelling difference between the asteroid and goddess. De Gasparis let his friend Ernesto Capocci name the asteroid to thank him for his encouragement.Charasteristics
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 asteroids in the "big four" (1 Ceres, 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.
Generally Hygiea's properties are the most poorly known out of the "big four" asteroids 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.[7]
Aspects
References
- 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).
- [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).
- A. Storrs et al, Imaging Observations of Asteroids with Hubble Space Telescope, Icarus, Vol. 137, p. 260 (1999).
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