6 Hebe
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Hebe (
minor planet designation A formal minor-planet designation is, in its final form, a number–name combination given to a minor planet (asteroid, centaur, trans-Neptunian object and dwarf planet but not comet). Such designation always features a leading number (catalog o ...
: 6 Hebe) is a large
main-belt The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, called ...
asteroid An asteroid is a minor planet of the Solar System#Inner solar system, inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic o ...
, containing around 0.5% of the mass of the belt. However, due to its apparently high bulk density (greater than that of the
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width ...
or even
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin atmos ...
), Hebe does not rank among the top twenty asteroids by volume. 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 – they tend to be loosely-bound
rubble pile In astronomy, a rubble pile is a celestial body that is not a monolith, consisting instead of numerous pieces of rock that have coalesced under the influence of gravity. Rubble piles have low density because there are large cavities between th ...
s. In
brightness Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light. In other words, brightness is the perception elicited by the luminance of a visual target. The perception is not linear to luminance, ...
, Hebe is the fifth-brightest object in the asteroid belt after
Vesta Vesta may refer to: Fiction and mythology * Vesta (mythology), Roman goddess of the hearth and home * Vesta (Marvel Comics), a Marvel Comics character * Sailor Vesta, a character in ''Sailor Moon'' Brands and products * Lada Vesta, a car from ...
, Ceres,
Iris Iris most often refers to: *Iris (anatomy), part of the eye *Iris (mythology), a Greek goddess * ''Iris'' (plant), a genus of flowering plants * Iris (color), an ambiguous color term Iris or IRIS may also refer to: Arts and media Fictional ent ...
, and
Pallas Pallas may refer to: Astronomy * 2 Pallas asteroid ** Pallas family, a group of asteroids that includes 2 Pallas * Pallas (crater), a crater on Earth's moon Mythology * Pallas (Giant), a son of Uranus and Gaia, killed and flayed by Athena * Pal ...
. It has a mean opposition magnitude of +8.3, about equal to the mean brightness of
Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fiction ...
, and can reach +7.5 at an opposition near perihelion. Hebe may be the parent body of the
H chondrite The H type ordinary chondrites are the most common type of meteorite, accounting for approximately 40% of all those catalogued, 46% of the ordinary chondrites, and 44% of all chondrites. The ordinary chondrites are thought to have originated from ...
meteorites, which account for about 40% of all
meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object en ...
s striking Earth.


History

Hebe was discovered on 1 July 1847 by
Karl Ludwig Hencke Karl Ludwig Hencke (8 April 1793 – 21 September 1866) was a German amateur astronomer and discoverer of minor planets. He is sometimes confused with Johann Franz Encke, another German astronomer. Biography Hencke was born in Driesen, Branden ...
, the sixth
asteroid An asteroid is a minor planet of the Solar System#Inner solar system, inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic o ...
discovered. It was the second and final asteroid discovery by Hencke, after
5 Astraea Astraea () (minor planet designation: 5 Astraea) is an asteroid in the asteroid belt. Its surface is highly reflective and its composition is probably a mixture of nickel–iron with silicates of magnesium and iron. It is an S-type asteroid in t ...
. The name '' Hebe'', goddess of youth, was proposed by
Carl Friedrich Gauss Johann Carl Friedrich Gauss (; german: Gauß ; la, Carolus Fridericus Gauss; 30 April 177723 February 1855) was a German mathematician and physicist who made significant contributions to many fields in mathematics and science. Sometimes refe ...
at Hencke's request. Gauss chose a
wineglass A wine glass is a type of glass that is used to drink and taste wine. Most wine glasses are stemware (goblets), i.e., they are composed of three parts: the bowl, stem, and foot. Shapes The effect of glass shape on the taste of wine has not been ...
as its symbol.


Potential as major meteorite source

Hebe was once thought to be the probable parent body of the
H chondrite The H type ordinary chondrites are the most common type of meteorite, accounting for approximately 40% of all those catalogued, 46% of the ordinary chondrites, and 44% of all chondrites. The ordinary chondrites are thought to have originated from ...
meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object en ...
s and the
IIE iron meteorite The iron meteorites of the IIE chemical type are octahedrites of various coarseness, most of which contain numerous inclusions of recrystallized stony silicates. Composition and origin They have mineral compositions and oxygen isotope ratios ve ...
s. This would imply that it is the source of about 40% of all meteorites striking Earth. Evidence for this connection includes the following: * 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 Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers ( mass number ...
ratios. * Asteroids with spectra similar to the
ordinary chondrite The ordinary chondrites (sometimes called the O chondrites) are a class of stony chondritic meteorites. They are by far the most numerous group, comprising 87% of all finds. Hence, they have been dubbed "ordinary". The ordinary chondrites are t ...
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 A Kirkwood gap is a gap or dip in the distribution of the semi-major axes (or equivalently of the orbital periods) of the orbits of main-belt asteroids. They correspond to the locations of orbital resonances with Jupiter. For example, there ...
at 2.50 AU and the nearby \nu_6\,\!
secular resonance A secular resonance is a type of orbital resonance between two bodies with synchronized precessional frequencies. In celestial mechanics, secular refers to the long-term motion of a system, and resonance is periods or frequencies being a simple nu ...
which determines the high-inclination edge of the
asteroid belt The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, called ...
at about 16°
inclinations Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Eart ...
hereabouts. * Of the asteroids in this "well-placed" orbit, Hebe is the largest. * An analysis of likely contributors to Earth's meteorite flux places 6 Hebe at the top of the list,A. Morbidelli et al. ''Delivery of meteorites through the ν6 secular resonance''
Astronomy & Astrophysics, Vol. 282, p. 955 (1994).
due to its position and relatively large size.M. J. Gaffey & S. L. Gilbert ''Asteroid 6 Hebe: The probable parent body of the H-Type ordinary chondrites and the IIE iron meteorites''
Meteoritics & Planetary Science, Vol. 33, p. 1281 (1998).
However, observations by the
VLT VLT may stand for: * Very Large Telescope array, in northern Chile * Vestmanlands Läns Tidning, newspaper in Västerås, Sweden * Video Lottery Terminal, for gambling on a video game * Virtual Link Trunking, proprietary networking protocol * Valle ...
in 2017 indicate that the depressions cause by impacts on 6 Hebe are only 20% the volume of the nearby H-chondrite asteroid families, suggesting the Hebe is not the most likely or primary source of H-chondrite meteorites.


Physical characteristics

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, with the north pole pointing towards
ecliptic coordinates The ecliptic coordinate system is a celestial coordinate system commonly used for representing the apparent positions, orbits, and pole orientations of Solar System objects. Because most planets (except Mercury) and many small Solar System bodi ...
(β, λ) = (45°, 339°) with a 10° uncertainty. This gives an
axial tilt In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orb ...
of 42°. It has a bright surface and, if its identification as the parent body of the H chondrites is correct, a surface composition of silicate
chondritic A chondrite is a stony (non-Metallicity, metallic) meteorite that has not been modified, by either melting or planetary differentiation, differentiation of the parent body. They are formed when various types of dust and small grains in the ea ...
rocks mixed with pieces of iron–nickel. A likely scenario for the formation of the surface metal is as follows: # Large impacts caused local melting of the iron rich H chondrite surface. The metals, being heavier, would have settled to the bottom of the magma lake, forming a metallic layer buried by a relatively shallow layer of silicates. # Later sizeable impacts broke up and mixed these layers. # Small frequent impacts tend to preferentially pulverize the weaker rocky debris, leading to an increased concentration of the larger metal fragments at the surface, such that they eventually comprise ~40% of the immediate surface at the present time.


Orbit

On 5 March 1977 Hebe
occulted An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks ...
Kaffaljidhma (γ Ceti), a moderately bright 3rd-
magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...
star. Between 1977 and 2021, 6 Hebe has been observed to
occult The occult, in the broadest sense, is a category of esoteric supernatural beliefs and practices which generally fall outside the scope of religion and science, encompassing phenomena involving otherworldly agency, such as magic and mysticism ...
fourteen stars.


Possible moon

As a result of the aforementioned 1977 occultation, a small
moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width ...
around Hebe was reported by
Paul D. Maley Paul may refer to: *Paul (given name), a given name (includes a list of people with that name) * Paul (surname), a list of people People Christianity *Paul the Apostle (AD c.5–c.64/65), also known as Saul of Tarsus or Saint Paul, early Chri ...
.W. R. Johnston ''Other reports of Asteroid/TNO Companions''
/ref> It was nicknamed "Jebe" (see
heebie-jeebies Heebie-jeebies is a phrase, widely attributed to Billy DeBeck, meaning a feeling of anxiety, apprehension, depression or illness. Heebie-jeebies or heebie jeebies may also refer to: *Heebie Jeebies (composition), "Heebie Jeebies" (composition), ...
). This was the first modern-day suggestion that asteroids have satellites. It was 17 years later when the first asteroid moon was formally discovered (Dactyl, the satellite of 243 Ida). The discovery of Hebe's moon was never confirmed. Detailed observations by many telescopes including the
Very Large Telescope The Very Large Telescope (VLT) is a telescope facility operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. It consists of four individual telescopes, each with a primary mirror 8.2 m across, ...
and the
Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most ver ...
have consistently failed to detect any satellites around the asteroid, casting doubt on such a moon existing.


See also

* Former classification of planets


Notes


References


External links


shape model deduced from lightcurve


(discovery announcement)


JPL Ephemeris
* * {{DEFAULTSORT:000006 Background asteroids Hebe Hebe S-type asteroids (Tholen) S-type asteroids (SMASS) 18470701 Objects observed by stellar occultation