34th Largest Asteroid, 6 Hebe

6 Hebe is a large main-belt asteroid and the 34th largest asteroid currently known.




Discovery

Hebe was the sixth asteroid to be discovered, on July 1, 1847 by Karl Ludwig Hencke at Driesen. It was the second and final asteroid discovery by Hencke, who had previously found 5 Astraea.

Naming

The name Hebe, goddess of youth, was proposed by Carl Friedrich Gauss, who was a German mathematician and physical scientist who contributed significantly to many fields, including number theory, statistics, analysis, differential geometry, geodesy, geophysics, electrostatics, astronomy and optics.

In Greek mythology, Hēbē is the goddess of youth (Roman equivalent: Juventas). She is the daughter of Zeus and Hera. Hebe was the cupbearer for the gods and goddesses of Mount Olympus, serving their nectar and ambrosia, until she was married to Heracles.

The name Hebe comes from Greek word meaning "youth" or "prime of life". Juventas likewise means "youth", as can be seen in such derivatives as juvenile. In art, Hebe is usually depicted wearing a sleeveless dress. Hebe was also worshipped as a goddess of pardons or forgiveness; freed prisoners would hang their chains in the sacred grove of her sanctuary at Phlius.

Stats

Diameter (mean): 185 km
Aphelion: 2.914 AU
Perihelion: 1.935 AU
Semi-major axis: 2.425 AU
Orbital Period: 3.78 years
Rotation period: 7.27 hrs
Date discovered: 1847.7.1
Class: S
Type: Main-belt Asteroid
Satellite: 1 ?
(data from JPL Small-Body Database)

Orbit and Brightness

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 and can reach +7.5 at an opposition near perihelion.

Physical characteristics

Hebe containing around half a percent of the mass of the asteroid belt. Hebe's size/volume does not rank among the top twenty asteroids. But its apparently high bulk density is even greater than that of the Earth's Moon or even Mars. 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, as they tend to be loosely bound rubble piles.

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.

Major meteorite source

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

- 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 oxygen isotope ratios.

- Asteroids with spectra similar to the ordinary 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 3:1 Kirkwood gap at 2.50 AU and the nearby secular resonance which determines the high-inclination edge of the asteroid 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, due to its position and relatively large size. If Hebe is not the H-chondrite parent body, then where are the meteorites from Hebe?

Satellite

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 Hebean moon was reported by Paul D. Maley. It was nicknamed "Jebe". However, the discovery has not been confirmed.