6 Hebe
6 Hebe is a large asteroid in the main asteroid belt, discovered on 1 July 1847 by German amateur astronomer Karl Ludwig Hencke using a modest telescope from his home in Driesen, Prussia (now Drezdenko, Poland). As the sixth asteroid identified after Ceres, Pallas, Juno, Vesta, and Astraea, it represents an early milestone in the exploration of minor bodies in the solar system. With an irregular triaxial shape measuring approximately 208 km × 184 km × 174 km and a volume-equivalent diameter of 193 ± 6 km, Hebe accounts for about 0.5% of the total mass of the asteroid belt, making it one of the belt's most massive members.[1] Hebe orbits the Sun in the inner main belt at a semi-major axis of 2.426 AU, with an eccentricity of 0.203 and an inclination of 14.74° relative to the ecliptic, resulting in a sidereal orbital period of 3.78 years (1,380 days).[2] Its highly inclined and eccentric path brings it as close as 1.94 AU to the Sun at perihelion and as far as 2.91 AU at aphelion, occasionally placing it within visual range from Earth at opposition with a brightness reaching magnitude 7.0, visible in small telescopes.[2] The asteroid rotates rapidly with a sidereal period of 7.274 hours, exhibiting a geometric albedo of about 0.25, consistent with its bright, stony surface.[1] Observations suggest a bulk density of approximately 3.5 g/cm³, indicating a composition dominated by silicate minerals with possible metallic components.[1] Spectroscopically, 6 Hebe is classified as an S-type asteroid in the Tholen scheme, specifically the S(IV) subtype, characterized by absorption features near 1 μm attributable to olivine and pyroxene. Its surface shows evidence of space weathering and minor hydration, but overall matches the H-type ordinary chondrites, leading to its proposal as the parent body for this meteorite class, which comprises about 34% of observed falls, as well as the IIE iron meteorites.[3] This connection implies that Hebe may have undergone collisional disruption in the past, contributing fragments to Earth via meteor streams, and its family of smaller asteroids supports this dynamical history. High-resolution imaging from the Very Large Telescope has revealed a large polar crater, potentially from a major impact, though the excavated volume is considered insufficient to fully account for the abundance of H-chondrite meteorites.[1]Discovery and History
Discovery
6 Hebe was discovered on 1 July 1847 by Karl Ludwig Hencke, a German amateur astronomer and retired postmaster, using a refractor telescope from his home observatory in Driesen, Prussia (now Drezdenko, Poland). Hencke's observation came during his systematic and prolonged search for additional minor planets, undertaken in the belief that more objects beyond the first four asteroids—Ceres (discovered 1801), Pallas (1802), Juno (1804), and Vesta (1807)—remained undiscovered in the region between Mars and Jupiter.[4] Having already succeeded with 5 Astraea in 1845 after 15 years of diligent effort, Hencke continued his methodical comparisons of star charts against the night sky, a pursuit that exemplified the perseverance required in early asteroid hunting despite widespread skepticism about further finds.[4] The object was faint enough to demand repeated observations over several nights to establish its motion relative to background stars and confirm it as a new solar system body rather than a misidentified star. Hencke promptly reported his positional measurements to the Berlin Observatory, where the discovery was verified through independent observations, providing the crucial validation needed to announce 6 Hebe as the sixth known asteroid. This rapid confirmation highlighted the collaborative network among European observatories that accelerated the recognition of new discoveries in the mid-19th century.[4]Naming and Early Observations
Upon its discovery, 6 Hebe was assigned the provisional designation reflecting its status as the sixth such object identified in the main asteroid belt. It was subsequently named after Hebe, the Greek goddess of youth and the cupbearer to the Olympian gods, who was the daughter of Zeus and Hera and personified eternal vitality.[5] This mythological naming convention followed the tradition established for earlier asteroids, emphasizing classical figures to denote their celestial significance. In the mid-19th century, 6 Hebe was initially classified as the sixth planet in the solar system, aligning with the era's understanding of small bodies between Mars and Jupiter as planetary additions to the known system. However, the rapid discovery of additional objects with similar orbital characteristics—reaching 15 by the end of 1851—prompted astronomers to reclassify these bodies collectively as asteroids, distinguishing them from the major planets due to their shared zone and minor sizes.[6] This shift marked a pivotal evolution in solar system nomenclature, reducing the planetary count and formalizing the asteroid belt concept. Early telescopic observations of 6 Hebe highlighted its visibility and provided foundational data on its properties. It ranks as the fifth-brightest asteroid overall, exhibiting a mean opposition magnitude of +8.3, which renders it observable with moderate amateur equipment under dark skies. A key event was its first recorded stellar occultation on 5 March 1977, when it passed in front of the 3.6-magnitude star γ Ceti, allowing observers in Mexico to time the ingress and egress for an estimated equatorial diameter of approximately 195 km based on the event's duration.[7][8] The identification of 6 Hebe on 1 July 1847 by Karl Ludwig Hencke signified a resurgence in asteroid hunting after a 40-year lull since the discovery of 4 Vesta in 1807, invigorating systematic searches that yielded 7 Iris just one month later on 13 August and 8 Flora on 18 October of the same year. This cluster of findings in 1847 accelerated the recognition of the asteroid belt's population density, transitioning asteroid studies from sporadic detections to a structured field of astronomical inquiry.[9]Orbital Characteristics
Orbital Elements
The orbital elements of 6 Hebe describe its elliptical path around the Sun within the inner main asteroid belt, with parameters determined from extensive astrometric observations and dynamical modeling. These elements are typically expressed in the Keplerian form relative to the ecliptic plane and the equinox of J2000.0, though they are computed for a specific epoch to account for perturbations from planets and other bodies.[2] As of the epoch JD 2460000.5 (February 24, 2023 00:00 UTC), the key orbital parameters are as follows, sourced from the JPL Small-Body Database solution with orbit ID 13 (based on 47,160 observations spanning 1891 to 2023).[10]| Parameter | Symbol | Value | Unit |
|---|---|---|---|
| Semi-major axis | a | 2.42524054 | AU |
| Eccentricity | e | 0.20275238 | - |
| Inclination | i | 14.73756424 | ° |
| Longitude of ascending node | Ω | 138.63826477 | ° |
| Argument of perihelion | ω | 239.54004370 | ° |
| Mean anomaly | M | 91.86528298 | ° |