532 Herculina

Infobox Planet | discovery=yes | physical_characteristics = yes | bgcolour=#FFFFC0 | name=532 Herculina
discoverer=Max Wolf
discovered=April 20, 1904
alt_names=1904 NY
mp_category=Main belt
epoch=22 November, 2003 (JD 2452600.5)
semimajor=2.7719820 AU
perihelion=2.29 AU
aphelion=3.26 AU
eccentricity=0.1777919
period=4.62 a
inclination=16.30843°
asc_node=107.65510°
arg_peri=76.86717°
mean_anomaly=142.15781°
avg_speed="unknown"
dimensions=225 km
mass=~2.29×10¹⁹Kg [http://www.ipa.nw.ru/PAGE/DEPFUND/LSBSS/engmasses.htm "Masses and densities of minor planets"] - Yu. Chernetenko, O. Kochetova, and V. Shor]
density=~4 g/cm³
surface_grav="unknown"
escape_velocity="unknown"
rotation=9.404951 h
spectral_type=S
magnitude = 8.82 cite web
title=Bright Minor Planets 2005
publisher=Minor Planet Center
url=http://www.cfa.harvard.edu/iau/Ephemerides/Bright/2005
accessdate=2008-05-21] to 11.99
abs_magnitude=5.81
albedo=0.16
angular_size = 0.228" to 0.073"
single_temperature="unknown"

532 Herculina "(herr'-kew-lye'-nə," IPAEng|ˈhɛrkjuˈlaɪnə) is a very large asteroid, with a diameter of around 225 km.

Discovery

It was discovered on April 20th, 1904, by Max Wolf in Heidelberg, and initially catalogued as 1904 NY. ["Provisional elements of the minor planet 1904 NY". J. C. Hammond, Astronomical Journal, vol. 24, iss. 564, p. 105-105 (1904) [http://adsabs.harvard.edu/abs/1904AJ.....24..105H ADS archive copy] ] The origin of its name is not known; it may be named after the mythical Hercules, or after an unknown woman of that name. The bulk of the asteroids discovered by Wolf around this date were named for characters in operas, but if this name was also drawn from such a source, no explanation has been recorded.

Physical characteristics

Herculina is one of the twenty or so largest members of the main asteroid belt. [ [http://www.earth.uni.edu/~morgan/astro/course/Notes/section4/asteroids.html 20 Largest Asteroids] ]

It has often been noted for its complex lightcurves, which made determination of its shape and rotation somewhat difficult. A set of 1982 speckle inferometry observations led to a simple preliminary model of Herculina as a three-axis object, perhaps 260 by 220 by 215 km. 1985 analysis of this data concluded there was a nonspherical shape with one bright spot, whilst a 1987 photometric astrometry study concluded the object was spherical with two dark spots (and rotated around a completely different pole), which was in turn negated by a 1988 thermal study which showed the object could not be spherical. By the late 1980s, the generally accepted model was a three-axis object with major albedo or topographical features. [ [http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19880013459_1988013459.pdf "Speckle interferometry of asteroids"] (NASA CR-180438). J. Drummond, Steward Observatory, University of Arizona, May 31, 1988]

Recent (2002) modelling of photometric data indicates that Herculina is not spherical, but a blocky shape not unlike a battered cuboid - or, as the analysis described it, it "resembles a toaster". This analysis indicates the presence of multiple largish craters, similar to 253 Mathilde, but no major variation in albedo. The approximate ratios of the axes were suggested as 1:1.1:1.3, broadly consistent with earlier models if slightly more elongated. [ [http://www.rni.helsinki.fi/~mjk/IcarPIII.pdf "Models of Twenty Asteroids from Photometric Data"] . M. Kaasalainen, J. Torppa, and J. Piironen, Icarus 159, 369–395 (2002).]

atellites

Following anomalous observations during an occultation of the star SAO 1220774 in 1978, Herculina became the first asteroid to be "confirmed" to have an asteroid moon, with the parent asteroid estimated at a 216km diameter and a satellite of about 45km orbiting at a distance of around 1,000 km. ["Satellite of Minor Planet 532 Herculina Discovered During Occultation". David W. Dunham, The Minor Planet Bulletin, Volume 6, p.13-14 (December 1978) [http://adsabs.harvard.edu/abs/1978MPBu....6...13D ADS archive copy] ] However, careful examination in 1993, using the Hubble Space Telescope, failed to locate a secondary. [ [http://web.mit.edu/bpweiss/www/asteroids.pdf "Imaging observations of asteroids with Hubble Space Telescope"] . Storrs "et.al.", Icarus 137, 260–268 (1999)]

References

External links

* [http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=532;orb=1 Orbital simulation] from JPL (Java) / [http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=sb&sstr=532 Ephemeris]