6 Hebe
Encyclopedia
6 Hebe is a large main-belt asteroid
, containing around half a percent of the mass of the belt. Its apparently high bulk density (greater than that of the Earth's Moon
or even Mars
), however, means that by volume it does not rank among the top twenty asteroids. 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
s.
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.
Hebe is probably the parent body of the H chondrite
meteorites, which account for a remarkable 40% of all meteorite
s striking the Earth.
Hebe was the sixth asteroid
to be discovered, on July 1, 1847 by Karl Ludwig Hencke
. It was the second and final asteroid discovery by Hencke, who had previously found 5 Astraea
. The name Hebe
, goddess of youth, was proposed by Carl Friedrich Gauss
.
meteorite
s and the IIE iron meteorite
s.
Remarkably, this would imply that it is the source of about 40% of all meteorites striking the Earth. Evidence for this connection includes the following (after Michael Gaffey and Sarah L. Gilbert.):
(β, λ) = (45°, 339°) with a 10° uncertainty. This gives an axial tilt
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 rocks mixed with pieces of nickel
-iron
metal
. A likely scenario for the formation of the surface metal is as follows:
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" (see Heebie Jeebies
). However, the discovery has not been confirmed.
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
, containing around half a percent of the mass of the belt. Its apparently high bulk density (greater than that of the Earth's Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
or even Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
), however, means that by volume it does not rank among the top twenty asteroids. 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
Rubble pile
In astronomy, rubble pile is the informal name for an object that is not a monolith, consisting instead of numerous pieces of rock that have coalesced under the influence of gravity...
s.
In brightness
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
, Hebe is the fifth brightest object in the asteroid belt after Vesta
4 Vesta
Vesta, formally designated 4 Vesta, is one of the largest asteroids, with a mean diameter of about . It was discovered by Heinrich Wilhelm Olbers on March 29, 1807, and is named after the Roman virgin goddess of home and hearth, Vesta....
, Ceres, Iris
7 Iris
7 Iris is a large main-belt asteroid. Among the S-type asteroids, it ranks fifth in geometric mean diameter after Eunomia, Juno, Amphitrite and Herculina....
and Pallas
2 Pallas
Pallas, formally designated 2 Pallas, is the second asteroid to have been discovered , and one of the largest. It is estimated to constitute 7% of the mass of the asteroid belt, and its diameter of 530–565 km is comparable to, or slightly larger than, that of 4 Vesta. It is however 20%...
. It has a mean opposition magnitude of +8.3, about equal to the mean brightness of Titan
Titan (moon)
Titan , or Saturn VI, is the largest moon of Saturn, the only natural satellite known to have a dense atmosphere, and the only object other than Earth for which clear evidence of stable bodies of surface liquid has been found....
and can reach +7.5 at an opposition near perihelion.
Hebe is probably the parent body of the H chondrite
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 the chondrites....
meteorites, which account for a remarkable 40% of all meteorite
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
s striking the Earth.
Discovery
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
to be discovered, on July 1, 1847 by Karl Ludwig Hencke
Karl Ludwig Hencke
Karl Ludwig Hencke was a German amateur astronomer. He is sometimes confused with Johann Franz Encke, another German astronomer....
. It was the second and final asteroid discovery by Hencke, who had previously found 5 Astraea
5 Astraea
5 Astraea is a large main-belt asteroid. Its surface is highly reflective and its composition is probably a mixture of nickel-iron with magnesium- and iron-silicates....
. The name Hebe
Hebe (mythology)
In Greek mythology, Hēbē is the goddess of youth . 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 ; her successor was the young Trojan prince Ganymede...
, goddess of youth, was proposed by Carl Friedrich Gauss
Carl Friedrich Gauss
Johann Carl Friedrich Gauss was a German mathematician and scientist who contributed significantly to many fields, including number theory, statistics, analysis, differential geometry, geodesy, geophysics, electrostatics, astronomy and optics.Sometimes referred to as the Princeps mathematicorum...
.
Major meteorite source
6 Hebe is the probable parent body of the H chondriteH 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 the chondrites....
meteorite
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
s and the IIE iron meteorite
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....
s.
Remarkably, this would imply that it is the source of about 40% of all meteorites striking the Earth. Evidence for this connection includes the following (after Michael Gaffey and Sarah L. Gilbert.):
- 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 differentiatedPlanetary differentiationIn planetary science, planetary differentiation is the process of separating out different constituents of a planetary body as a consequence of their physical or chemical behaviour, where the body develops into compositionally distinct layers; the denser materials of a planet sink to the center,...
asteroid. - The IIE irons and H chondrites likely come from the same parent body, due to similar trace mineral and oxygen isotopeIsotopeIsotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
ratios. - Asteroids with spectra similar to the ordinary chondriteOrdinary chondriteThe Ordinary chondrites are a class of stony chondritic meteorites. They are by far the most numerous group and comprise about 87% of all finds...
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 gapKirkwood gapA Kirkwood gap is a gap or dip in the distribution of main-belt asteroids with semi-major axis , as seen in the histogram below...
at 2.50 AUAstronomical unitAn astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
and the nearby
secular resonanceSecular resonanceA secular resonance is a type of orbital resonance.Secular resonances occur when the precession of two orbits is synchronised . A small body in secular resonance with a much larger one will precess at the same rate as the large body...
which determines the high-inclination edge of the asteroid beltAsteroid beltThe asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets...
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?
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 coordinatesEcliptic coordinate system
The ecliptic coordinate system is a celestial coordinate system that uses the ecliptic for its fundamental plane. The ecliptic is the path that the sun appears to follow across the celestial sphere over the course of a year. It is also the intersection of the Earth's orbital plane and the celestial...
(β, λ) = (45°, 339°) with a 10° uncertainty. This gives an axial tilt
Axial tilt
In astronomy, axial tilt is the angle between an object's rotational axis, and a line perpendicular to its orbital plane...
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
Silicate
A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...
chondritic rocks mixed with pieces of nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
-iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
. 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.
Moon
On March 5, 1977 Hebe occultedOccultation
An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...
Kaffaljidhma (γ Ceti
Gamma Ceti
Gamma Ceti is a star in the constellation Cetus. It has the traditional name Kaffaljidhma. The title Kaffaljidhma was derived from Arabic الكف الجذماء Al Kaff al Jidhmah, "The cut-short hand", the association of this star, along with α Cet , δ Cet, λ Cet , μ Cet, ξ1 Cet and ξ2 Cet..According to...
), a moderately bright 3rd magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
. No other observed occultations by Hebe have been reported.
As a result of that occultation, a small Hebean moon
Natural satellite
A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....
was reported by Paul D. Maley. It was nicknamed "Jebe" (see Heebie Jeebies
Heebie Jeebies
Heebie-jeebies or heebie jeebies may refer to:*Heebie-jeebies , used to describe a feeling of anxiety, apprehension, depression or illness.*"Heebie Jeebies" , a 1926 single by Louis Armstrong and his Hot Five...
). However, the discovery has not been confirmed.
External links
- shape model deduced from lightcurve
- MNRAS 7 (1847) 283 (discovery announcement)
- MNRAS 8 (1848) 103