Massalia family
Encyclopedia
The Massalia family of asteroids
is a grouping of S-type
asteroid
s in the inner main belt at very low inclination. About 0.8% of known asteroids belong to this family.
This is a definite cratering family consisting of 20 Massalia
and a mass of small fragments excavated from Massalia's surface by an impact. Massalia is by far the largest member with a diameter of about 150 km, while the next largest body, is only about 7 km in diameter. The mass of all the small members is negligible, less than about 1%, compared to Massalia.
The family is fairly young, estimated to have been created by an impact 150 to 200 million years ago. It has a distinctly two-lobed appearance in proper a--e space, with one lobe centered at semi-major axes of 2.38 AU, the other at about 2.43 AU, with the parent body Massalia itself located in between. The bodies in the lobes tend to be smaller on average than those in the central region. It has been shown that this structure is likely caused by slow drift of the semi-major axis caused by the Yarkovsky
and YORP effects. Details of the lobes were used to calculate the age of the family.
A strong 1:2 orbital resonance
with Mars
crosses the family at 2.42 AU
, and appears responsible for some "leakage" of family members away from the area into higher inclination orbits.
The Massalia family or a recent minor collision within it may be the source for the prominent α dust band
, the other candidate being a recent collision within the Themis family
.
with Mars
.
A HCM numerical analysis by Zappalà et al. determined a group of 'core' family members, whose proper orbital elements
lie in the approximate ranges
! !! ap
!! ep !! ip
>
min
2.37 AU
0.143
1.2°
max
2.45 AU
0.175*
1.75°
At the present epoch
, the range of osculating
orbital elements
of these core members is
The Zappalà 1995 analysis found 42 core members, while a search of a recent proper element database for 96944 minor planet
s in 2005 yielded 761 objects lying within the rectangular-shaped region defined by the first table above. This would give about 0.8% of all main belt asteroids.
and some other bodies were noted as interlopers during a detailed study of the family, while 2316 Jo-Ann
is seen to have the wrong spectrum by inspection of the PDS asteroid taxonomy data set. Muchachos is larger than any of the true family members apart from Massalia itself.
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 S-type
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:...
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 the inner main belt at very low inclination. About 0.8% of known asteroids belong to this family.
Characteristics
20 Massalia
20 Massalia is a large and fairly bright main-belt asteroid. It is also the largest member of the Massalia family of asteroids. Its name is the Greek name for Marseille, the city from which one of the two independent co-discovers, Jean Chacornac, first sighted it.- Characteristics :Massalia is an...
and a mass of small fragments excavated from Massalia's surface by an impact. Massalia is by far the largest member with a diameter of about 150 km, while the next largest body, is only about 7 km in diameter. The mass of all the small members is negligible, less than about 1%, compared to Massalia.
The family is fairly young, estimated to have been created by an impact 150 to 200 million years ago. It has a distinctly two-lobed appearance in proper a--e space, with one lobe centered at semi-major axes of 2.38 AU, the other at about 2.43 AU, with the parent body Massalia itself located in between. The bodies in the lobes tend to be smaller on average than those in the central region. It has been shown that this structure is likely caused by slow drift of the semi-major axis caused by the Yarkovsky
Yarkovsky effect
The Yarkovsky effect is a force acting on a rotating body in space caused by the anisotropic emission of thermal photons, which carry momentum...
and YORP effects. Details of the lobes were used to calculate the age of the family.
A strong 1:2 orbital resonance
Orbital resonance
In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of...
with 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...
crosses the family at 2.42 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
, and appears responsible for some "leakage" of family members away from the area into higher inclination orbits.
The Massalia family or a recent minor collision within it may be the source for the prominent α dust band
Interplanetary dust cloud
The interplanetary dust cloud is cosmic dust which pervades the space between planets in the Solar System and in other planetary systems...
, the other candidate being a recent collision within the Themis family
Themis family
The Themis or Themistian Asteroid Family is a Hirayama family of asteroids found in the outer portion of the main asteroid belt, between the orbits of Mars and Jupiter. At a mean distance of 3.13 AU from the Sun, it is one of the more populous asteroid families...
.
Location and size
The Massalian asteroids are located at very low inclinations, straddling the 1:2 resonancesOrbital resonance
In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of...
with 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...
.
A HCM numerical analysis by Zappalà et al. determined a group of 'core' family members, whose proper orbital elements
Proper 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....
- * The Zappalà core members only reach e=0.170 but inspection of more modern proper elements reveals that the family extends at least to e=0.175
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 | 2.37 AU Astronomical unit An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance.... |
0.124 | 0.4° |
| max | 2.45 AU | 0.211 | 2.35° |
The Zappalà 1995 analysis found 42 core members, while a search of a recent proper element database 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 761 objects lying within the rectangular-shaped region defined by the first table above. This would give about 0.8% of all main belt asteroids.
Interlopers
A number of interlopers have been identified, which share the same orbital elements as the true family members, but cannot have come from the same cratering event because of spectral (hence, compositional) differences. 2946 Muchachos2946 Muchachos
2946 Muchachos is a main-belt asteroid discovered on October 15, 1941 by L. Oterma at Turku.- External links :*...
and some other bodies were noted as interlopers during a detailed study of the family, while 2316 Jo-Ann
2316 Jo-Ann
2316 Jo-Ann is a main belt asteroid with an orbital period of 1402.5558542 days . The asteroid was discovered on September 2, 1980.-References:...
is seen to have the wrong spectrum by inspection of the PDS asteroid taxonomy data set. Muchachos is larger than any of the true family members apart from Massalia itself.