Hygiea family
Encyclopedia
The Hygiea family of asteroids
is a grouping of dark, carbonaceous
C-type
and B-type
asteroid
s in outer main belt, the largest member of which is 10 Hygiea
. About 1% of all known main belt asteroids belong to this family.
By far the largest member is 10 Hygiea
, a 400 km diameter C-type asteroid
that is the fourth largest in the belt. The remaining members are relatively much smaller so Hygiea contains about 94-98% of the mass in the family (depending on the exact criteria for inclusion). The two next largest members are 333 Badenia
, and 538 Friederike
, both just over 70 km in diameter. After that, the remaining members have diameters of less than 30 km.
The family is thought to be of the cratering type, implying that it was formed as a result of a giant impact that excavated the much smaller family members from Hygiea (Zappala 1995, Farinella 1996). However, the two 70 km diameter bodies are still surprisingly large to have been excavated in an impact that did not disrupt the parent body (compare e.g. to the Vesta family
, which contains no members above around 10 km diameter). They may be interlopers (see below) despite having a similar spectral type to Hygiea, as dark carbonaceous asteroids dominate the outer main belt anyway.
The family contains a significant number of objects of the otherwise rare B spectral type
(Mothé-Diniz 2001). The largest of these is the previously mentioned 538 Friederike
.
There are some indications that this family is relatively quite old (Tanga 1999).
lie in the approximate ranges
! !! ap
!! ep !! ip
>
min
3.06 AU
0.109
4.2°
max
3.22 AU
0.163
5.8°
At the present epoch
, the range of osculating
orbital elements
of these core members is
The Zappalà 1995 analysis found 103 core members, while a search of a recent proper element database (AstDys)for 96944 minor planet
s in 2005 yielded 1043 objects lying within the rectangular-shaped region defined by the first table above. This would give about 1% of all main belt asteroids.
S-
and D-type
members: 100 Hekate
, 108 Hecuba
, 1109 Tata
, 1209 Pumma
, and 1599 Giomus
.
In fact, some of the other asteroids of the C spectral type are probably interlopers as well, due to the prevalence of this spectral type in the region. Possible candidates include 333 Badenia
and 538 Friederike
, based on their unusually large size for cratering family members.
52 Europa
, a very large 300 km diameter asteroid orbits nearby with a proper inclination of 6.37°, and was sometimes considered part of the Hygiea family in the past, but it is an unrelated asteroid. A better sampling of asteroids in the area in recent years has clearly shown that it orbits well beyond the Hygiea family clump.
Asteroid family
An asteroid family is a population of asteroids that share similar proper orbital elements, such as semimajor axis, eccentricity, and orbital inclination. The members of the families are thought to be fragments of past asteroid collisions...
is a grouping of dark, carbonaceous
Carbonaceous
Carbonaceous is the defining attribute of a substance rich in carbon. Particularly, carbonaceous hydrocarbons are very unsaturated, high-molecular-weight hydrocarbons, having an elevated carbon:hydrogen ratio....
C-type
C-type asteroid
C-type asteroids are carbonaceous asteroids. They are the most common variety, forming around 75% of known asteroids, and an even higher percentage in the outer part of the asteroid belt beyond 2.7 AU, which is dominated by this asteroid type...
and B-type
B-type asteroid
B-type asteroids are a relatively uncommon type of carbonaceous asteroid, falling into the wider C-group. In the asteroid population, B-class objects are abundant in the outer asteroid belt, and also dominate the high-inclination Pallas family which includes the second-largest asteroid 2 Pallas...
asteroid
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...
s in outer main belt, the largest member of which is 10 Hygiea
10 Hygiea
10 Hygiea is an asteroid located in the asteroid belt. With somewhat oblong diameters of 350–500 km, and a mass estimated to be 2.9% of the total mass of the belt, it is the fourth largest asteroid by volume and mass...
. About 1% of all known main belt asteroids belong to this family.
Characteristics
10 Hygiea
10 Hygiea is an asteroid located in the asteroid belt. With somewhat oblong diameters of 350–500 km, and a mass estimated to be 2.9% of the total mass of the belt, it is the fourth largest asteroid by volume and mass...
, a 400 km diameter C-type asteroid
C-type asteroid
C-type asteroids are carbonaceous asteroids. They are the most common variety, forming around 75% of known asteroids, and an even higher percentage in the outer part of the asteroid belt beyond 2.7 AU, which is dominated by this asteroid type...
that is the fourth largest in the belt. The remaining members are relatively much smaller so Hygiea contains about 94-98% of the mass in the family (depending on the exact criteria for inclusion). The two next largest members are 333 Badenia
333 Badenia
333 Badenia is a large C-type asteroid in the outer asteroid belt.It was discovered by Max Wolf on August 22, 1892 in Heidelberg.-References:###...
, and 538 Friederike
538 Friederike
- References :# # # #...
, both just over 70 km in diameter. After that, the remaining members have diameters of less than 30 km.
The family is thought to be of the cratering type, implying that it was formed as a result of a giant impact that excavated the much smaller family members from Hygiea (Zappala 1995, Farinella 1996). However, the two 70 km diameter bodies are still surprisingly large to have been excavated in an impact that did not disrupt the parent body (compare e.g. to the Vesta family
Vesta family
The Vesta or Vestian family of asteroids is a large and prominent grouping of mostly V-type asteroids in the inner asteroid belt in the vicinity of 4 Vesta...
, which contains no members above around 10 km diameter). They may be interlopers (see below) despite having a similar spectral type to Hygiea, as dark carbonaceous asteroids dominate the outer main belt anyway.
The family contains a significant number of objects of the otherwise rare B spectral type
B-type asteroid
B-type asteroids are a relatively uncommon type of carbonaceous asteroid, falling into the wider C-group. In the asteroid population, B-class objects are abundant in the outer asteroid belt, and also dominate the high-inclination Pallas family which includes the second-largest asteroid 2 Pallas...
(Mothé-Diniz 2001). The largest of these is the previously mentioned 538 Friederike
538 Friederike
- References :# # # #...
.
There are some indications that this family is relatively quite old (Tanga 1999).
Location and size
A HCM numerical analysis by (Zappala 1995) found a 'core' group of family members, whose proper orbital elementsProper orbital elements
The proper orbital elements of an orbit are constants of motion of an object in space that remain practically unchanged over an astronomically long timescale...
lie in the approximate ranges
Semi-major axis
The major axis of an ellipse is its longest diameter, a line that runs through the centre and both foci, its ends being at the widest points of the shape...
!! ep !! ip
Inclination
Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
>
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
At the present epoch
Epoch (astronomy)
In astronomy, an epoch is a moment in time used as a reference point for some time-varying astronomical quantity, such as celestial coordinates, or elliptical orbital elements of a celestial body, where these are subject to perturbations and vary with time...
, the range of osculating
Osculating orbit
In astronomy, and in particular in astrodynamics, the osculating orbit of an object in space is the gravitational Kepler orbit In astronomy, and in particular in astrodynamics, the osculating orbit of an object in space (at a given moment of time) is the gravitational Kepler orbit In astronomy,...
orbital elements
Orbital elements
Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are generally considered in classical two-body systems, where a Kepler orbit is used...
of these core members is
| a Semi-major axis The major axis of an ellipse is its longest diameter, a line that runs through the centre and both foci, its ends being at the widest points of the shape... | e | i Inclination Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit... |
|
|---|---|---|---|
| min | 3.06 AU Astronomical unit An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance.... |
0.088 | 3.5° |
| max | 3.24 AU | 0.191 | 6.8° |
The Zappalà 1995 analysis found 103 core members, while a search of a recent proper element database (AstDys)for 96944 minor planet
Minor planet
An asteroid group or minor-planet group is a population of minor planets that have a share broadly similar orbits. Members are generally unrelated to each other, unlike in an asteroid family, which often results from the break-up of a single asteroid...
s in 2005 yielded 1043 objects lying within the rectangular-shaped region defined by the first table above. This would give about 1% of all main belt asteroids.
Interlopers
This family contains quite a large number of identified interlopers. The following have been identified in a spectral survey (Mothé-Diniz 2001), and also by inspection of the PDS asteroid taxonomy data set forS-
S-type asteroid
S-type asteroids are of a stony composition, hence the name. Approximately 17% of asteroids are of this type, making it the second most common after the C-type.-Characteristics:...
and D-type
D-type asteroid
D-type asteroids have a very low albedo and a featureless reddish electromagnetic spectrum. It has been suggested that they have a composition of organic rich silicates, carbon and anhydrous silicates, possibly with water ice in their interiors...
members: 100 Hekate
100 Hekate
100 Hekate is a large main-belt asteroid. It orbits in the same region of space as the Hygiea asteroid family, though it is actually an unrelated interloper. Its albedo of 0.19 is too high, and it is of the wrong spectral class to be part of the dark carbonaceous Hygiea family.Hekate was the...
, 108 Hecuba
108 Hecuba
108 Hecuba is a fairly large and bright main-belt asteroid.Hecuba orbits within the Hygiea family of asteroids but is not otherwise related to other family members because it has a silicate composition; Hygieas are dark C-type asteroids....
, 1109 Tata
1109 Tata
1109 Tata is a main belt asteroid orbiting the Sun. It was discovered by Karl Wilhelm Reinmuth on February 5, 1929 at Heidelberg, Germany. Its provisional designation was 1929 CU. The origin of its name is unknown.-References:...
, 1209 Pumma
1209 Pumma
1209 Pumma is a main-belt asteroid discovered on April 22, 1927 by K. Reinmuth at Heidelberg.- External links :*...
, and 1599 Giomus
1599 Giomus
1599 Giomus is a main-belt asteroid discovered on November 17, 1950 by Boyer, L. at Algiers.- External links :*...
.
In fact, some of the other asteroids of the C spectral type are probably interlopers as well, due to the prevalence of this spectral type in the region. Possible candidates include 333 Badenia
333 Badenia
333 Badenia is a large C-type asteroid in the outer asteroid belt.It was discovered by Max Wolf on August 22, 1892 in Heidelberg.-References:###...
and 538 Friederike
538 Friederike
- References :# # # #...
, based on their unusually large size for cratering family members.
52 Europa
52 Europa
52 Europa is one of the larger asteroids in the asteroid belt, having a diameter of 300 km. It was discovered on February 4, 1858, by Hermann Goldschmidt from his balcony in Paris...
, a very large 300 km diameter asteroid orbits nearby with a proper inclination of 6.37°, and was sometimes considered part of the Hygiea family in the past, but it is an unrelated asteroid. A better sampling of asteroids in the area in recent years has clearly shown that it orbits well beyond the Hygiea family clump.