Eos family
Encyclopedia
The Eos or Eoan family is a prominent family
of main belt
asteroid
s that is believed to have formed as a result of an ancient catastrophic collision. Members of the family share similar orbits. The family is named after 221 Eos
.
In 1918, while the Japanese astronomer Kiyotsugu Hirayama
was studying at Yale University
, he began to examine asteroid motions. By plotting the mean motion, eccentricity
and inclination
of the asteroid orbits, he discovered that some of the objects formed groupings. In a 1918 paper, he described three such groups, including the Eos family with 19 members. Since that time, the number of members in the Eos family grouping has continued to grow, reaching 289 by 1993.
The Eos family asteroids have semi-major axes
between 2.99 and 3.03 Astronomical Unit
s, eccentricities
between 0.01 and 0.13, and inclination
s between 8° and 12°. Currently there are about 4,400 members known. The inner orbit of the family is bracketed by the 7/3 mean-motion resonance with Jupiter at 2.96 AU. The orbital range also includes the 9/4 mean-motion resonance with Jupiter at 3.03 AU. Most of the family members lie within the latter orbital distance. The distribution of asteroid sizes suggests that the family is about 1–2 billion years old.
Kiyotsugu Hirayama hypothesized that these asteroid families were formed by a catastrophic collision with a parent body. This interpretation is still accepted today by the astronomy community. Observations of the Eos family show that they have a similar spectroscopic signature. Variation in the spectra is interpreted as compositional variation resulting from the partial differentiation of the parent body. That is, prior to the breakup, the parent body was partly segregated with denser materials moving toward the core. Since the breakup, the family members have undergone space weathering
.
Asteroids in the Eos family resemble the S-type asteroid
category. However, examination of Eos and other family members in the infrared
show some differences with the S-type. As a result, the Eos family have been given their own category of K-type asteroids. In terms of meteorite
s collected on Earth, this category may be related to the CO3 or CV3 chondrites, instead of the OC type. Objects that share similar orbits with the Eos family but do not have this spectrum are assumed to be random interlopers.
The rotation rates of the Eos family asteroids are randomly distributed. This randomization resulted from subsequent collisions with other bodies, implying that the asteroids retain some "memory" of the rotation rate of the parent body. Thus the original object had a rotation rate of about 1–3 days. Evolutionary models of this spread in the rotation rate of the Eos family implies that this group may be comparable to the age of the Solar System
. Numerical simulations of the collision that created the Eos family suggest that the smaller body was about a tenth the mass of the parent and struck from a direction out of the ecliptic plane. The parent object had an estimated diameter of 240 km. The best fit model implies a family age of 1.1 billion years.
Members of the Eos family include the asteroids 221 Eos
, 339 Dorothea
, 450 Brigitta
, 513 Centesima
, 562 Salome
, 633 Zelima
, 639 Latona
, 651 Antikleia
, 653 Berenike
, 661 Cloelia
, 669 Kypria
, 742 Edisona
, 807 Ceraskia
, 876 Scott
and 890 Waltraut
. Not all fragments of the original parent body have remained in the orbital zone occupied by the Eos family. Spectroscopic analysis has shown that some of these asteroids are now located in the 9/4 mean-motion resonance with Jupiter
. These fugitives appear relatively young compared to the other family members.
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...
of main belt
Asteroid belt
The 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...
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 that is believed to have formed as a result of an ancient catastrophic collision. Members of the family share similar orbits. The family is named after 221 Eos
221 Eos
221 Eos is a rather large main-belt asteroid. It is classified as a K-type asteroid. It is a member of the extensive Eos asteroid family, which is named after it.Eos was discovered by Johann Palisa on January 18, 1882, in Vienna...
.
In 1918, while the Japanese astronomer Kiyotsugu Hirayama
Kiyotsugu Hirayama
was a Japanese astronomer, best known for his discovery that many asteroid orbits were more similar to one another than chance would allow, leading to the concept of asteroid families, now called "Hirayama families" in his honour....
was studying at Yale University
Yale University
Yale University is a private, Ivy League university located in New Haven, Connecticut, United States. Founded in 1701 in the Colony of Connecticut, the university is the third-oldest institution of higher education in the United States...
, he began to examine asteroid motions. By plotting the mean motion, eccentricity
Orbital eccentricity
The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
and inclination
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...
of the asteroid orbits, he discovered that some of the objects formed groupings. In a 1918 paper, he described three such groups, including the Eos family with 19 members. Since that time, the number of members in the Eos family grouping has continued to grow, reaching 289 by 1993.
The Eos family asteroids have semi-major axes
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...
between 2.99 and 3.03 Astronomical Unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
s, eccentricities
Orbital eccentricity
The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
between 0.01 and 0.13, and inclination
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...
s between 8° and 12°. Currently there are about 4,400 members known. The inner orbit of the family is bracketed by the 7/3 mean-motion resonance with Jupiter at 2.96 AU. The orbital range also includes the 9/4 mean-motion resonance with Jupiter at 3.03 AU. Most of the family members lie within the latter orbital distance. The distribution of asteroid sizes suggests that the family is about 1–2 billion years old.
Kiyotsugu Hirayama hypothesized that these asteroid families were formed by a catastrophic collision with a parent body. This interpretation is still accepted today by the astronomy community. Observations of the Eos family show that they have a similar spectroscopic signature. Variation in the spectra is interpreted as compositional variation resulting from the partial differentiation of the parent body. That is, prior to the breakup, the parent body was partly segregated with denser materials moving toward the core. Since the breakup, the family members have undergone space weathering
Space weathering
Space weathering is a blanket term used for a number of processes that act on any body exposed to the harsh space environment. Airless bodies incur many weathering processes:* collisions of galactic cosmic rays and solar cosmic rays,* irradiation, implantation, and sputtering from solar wind...
.
Asteroids in the Eos family resemble the S-type asteroid
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:...
category. However, examination of Eos and other family members in the infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
show some differences with the S-type. As a result, the Eos family have been given their own category of K-type asteroids. In terms of 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 collected on Earth, this category may be related to the CO3 or CV3 chondrites, instead of the OC type. Objects that share similar orbits with the Eos family but do not have this spectrum are assumed to be random interlopers.
The rotation rates of the Eos family asteroids are randomly distributed. This randomization resulted from subsequent collisions with other bodies, implying that the asteroids retain some "memory" of the rotation rate of the parent body. Thus the original object had a rotation rate of about 1–3 days. Evolutionary models of this spread in the rotation rate of the Eos family implies that this group may be comparable to the age of the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
. Numerical simulations of the collision that created the Eos family suggest that the smaller body was about a tenth the mass of the parent and struck from a direction out of the ecliptic plane. The parent object had an estimated diameter of 240 km. The best fit model implies a family age of 1.1 billion years.
Members of the Eos family include the asteroids 221 Eos
221 Eos
221 Eos is a rather large main-belt asteroid. It is classified as a K-type asteroid. It is a member of the extensive Eos asteroid family, which is named after it.Eos was discovered by Johann Palisa on January 18, 1882, in Vienna...
, 339 Dorothea
339 Dorothea
339 Dorothea is a typical Main belt asteroid.It was discovered by Max Wolf on September 25, 1892 in Heidelberg, Germany....
, 450 Brigitta
450 Brigitta
450 Brigitta is a typical Main belt asteroid.It was discovered by Max Wolf and A. Schwassmann on October 10, 1899 in Heidelberg....
, 513 Centesima
513 Centesima
513 Centesima is a minor planet orbiting the Sun....
, 562 Salome
562 Salome
-External links:*...
, 633 Zelima
633 Zelima
633 Zelima is a minor planet orbiting the Sun in the asteroid belt with a magnitude of 10.7.-External links:*...
, 639 Latona
639 Latona
-External links:* -References:...
, 651 Antikleia
651 Antikleia
651 Antikleia is a main-belt asteroid discovered on October 4, 1907 by August Kopff at the Heidelberg-Königstuhl State Observatory. It is named for Anticlea the mother of Odysseus.- References :...
, 653 Berenike
653 Berenike
653 Berenike is a main-belt asteroid discovered on November 27, 1907 by Joel Hastings Metcalf at Taunton, Massachusetts. It is named after Berenice II of Egypt, after whom the constellation Coma Berenices is also named.- References :...
, 661 Cloelia
661 Cloelia
-External links:*...
, 669 Kypria
669 Kypria
-External links:*...
, 742 Edisona
742 Edisona
-External links:*...
, 807 Ceraskia
807 Ceraskia
-External links:*...
, 876 Scott
876 Scott
-External links:*...
and 890 Waltraut
890 Waltraut
890 Waltraut is a minor planet orbiting the Sun. It was named for a character in Richard Wagner's opera, Götterdämmerung or Twilight of the Gods....
. Not all fragments of the original parent body have remained in the orbital zone occupied by the Eos family. Spectroscopic analysis has shown that some of these asteroids are now located in the 9/4 mean-motion resonance with Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
. These fugitives appear relatively young compared to the other family members.