10 Hygiea
Encyclopedia
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. It is the largest of the class of dark C-type asteroid
s with a carbonaceous
surface.
Despite its size, due to its dark surface and larger-than-average distance from the Sun
, it appears very dim when observed from Earth. For this reason several smaller asteroids were observed before Annibale de Gasparis
discovered Hygiea on April 12, 1849. At most oppositions, Hygiea has a magnitude
that is four orders lower than Vesta's, and observing it will require at least a 100 mm (4-inch) telescope
, while at a perihelic opposition, it may be observable with 10x50 binoculars
.
on April 12, 1849, in Naples
, Italy
. It was the first of his nine asteroid discoveries. The director of the Naples observatory, Ernesto Capocci, named the asteroid. He chose to call it Igea Borbonica ("Bourbon
Hygieia") in honor of the ruling family of the Kingdom of the Two Sicilies where Naples was located.
However, in 1852, John Russell Hind
wrote that "it is universally termed Hygeia, the unnecessary appendage 'Borbonica' being dropped." The name comes from Hygieia
, the Greek goddess
of health, daughter of Asclepius
(Aesculapius for the Romans). The name was often spelled Hygeia in the nineteenth century, for example in the Monthly Notices of the Royal Astronomical Society.
Hygiea's surface is composed of primitive carbonaceous
material similar to the chondrite
meteorite
s. Aqueous alteration products have been detected on its surface, which could indicate the presence of water ice in the past which was heated sufficiently to melt. The primitive present surface composition would indicate that Hygiea had not been melted during the early period of Solar system formation, in contrast to other large planetesimal
s like 4 Vesta
.
It is the main member of the Hygiea family
and contains almost all the mass in this family (well over 90%). It is the largest of the class of dark C-type asteroid
s with a carbonaceous
surface that are dominant in the outer asteroid belt
—which lie beyond the Kirkwood gap
at 2.82 AU. Hygiea appears to have a noticeably oblate spheroid shape, with an average diameter of 444 ± 35 km and a semimajor axis ratio of 1.11. This is much more than for the other objects in the "big four"—the dwarf planet
Ceres and the asteroids 2 Pallas
and 4 Vesta
. Aside from being the smallest of the four, Hygiea, like Ceres, has a relatively low density, which is more comparable to the icy satellites of Jupiter
or Saturn
than to the terrestrial planet
s or the stony asteroids.
While it is the largest body in its region, due to its dark surface and larger-than-average distance from the Sun it appears very dim when observed from Earth. In fact, it is the third dimmest of the first twenty-three asteroids discovered, only 13 Egeria
and 17 Thetis
having lower mean opposition magnitude
s. At most oppositions, Hygiea has a magnitude
of around +10.2, which is as much as four orders fainter than Vesta, and will require at least a 4 inches (101.6 mm) telescope
to resolve. At a perihelic opposition, however, Hygiea can reach +9.1 and may just be resolvable with 10x50 binoculars
, unlike the next two largest asteroids in the asteroid belt, 704 Interamnia
and 511 Davida
, which are always beyond binocular visibility.
At least 5 stellar
occultation
s by Hygiea were tracked by Earth-based observers, but all with few observing independent measurements so that much was not learned of its shape. The Hubble Space Telescope
was able to resolve the asteroid, and to rule out the presence of any orbiting companions larger than about 16 km in diameter.
than those of Ceres, Pallas or Interamnia, but is less circular than Ceres or Vesta with an eccentricity of around 12%. Its perihelion
is at a quite similar longitude to those of Vesta and Ceres, though its ascending and descending nodes are opposite to the corresponding ones for those objects. Although its perihelion is extremely close to the mean distance of Ceres and Pallas, a collision between Hygiea and its larger companions is impossible because at that distance they are always on opposite sides of the ecliptic. Though in 2056, Hygiea will pass 0.025AU from Ceres, and then in 2063, Hygiea will pass 0.020AU from Pallas. At aphelion
Hygiea reaches out to the extreme edge of the asteroid belt at the perihelia of the Hilda family
which is in 3:2 resonance with Jupiter.
It is an unusually slow rotator, taking 27 hours and 37 minutes for a revolution, whereas 6 to 12 hours are more typical for large asteroids. Its direction of rotation is not certain at present, due to a twofold ambiguity in lightcurve data that is exacerbated by its long rotation period—which makes single-night telescope observations span at best only a fraction of a full rotation—but it is believed to be retrograde
. Lightcurve analysis indicates that Hygiea's pole points towards either ecliptic coordinates
(β, λ) = (30°, 115°) or (30°, 300°) with a 10° uncertainty. This gives an axial tilt
of about 60° in both cases.
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...
located in the asteroid 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...
. 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. It is the largest of the class of dark 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...
s with a 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....
surface.
Despite its size, due to its dark surface and larger-than-average distance from the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
, it appears very dim when observed from Earth. For this reason several smaller asteroids were observed before Annibale de Gasparis
Annibale de Gasparis
Annibale de Gasparis was an Italian astronomer. From 1864 to 1889 he was the director of the Astronomical Observatory of Capodimonte in Naples.He won the Gold Medal of the Royal Astronomical Society in 1851....
discovered Hygiea on April 12, 1849. At most oppositions, Hygiea has a 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...
that is four orders lower than Vesta's, and observing it will require at least a 100 mm (4-inch) telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
, while at a perihelic opposition, it may be observable with 10x50 binoculars
Binoculars
Binoculars, field glasses or binocular telescopes are a pair of identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes when viewing distant objects...
.
Discovery and name
Hygiea was discovered by Annibale de GasparisAnnibale de Gasparis
Annibale de Gasparis was an Italian astronomer. From 1864 to 1889 he was the director of the Astronomical Observatory of Capodimonte in Naples.He won the Gold Medal of the Royal Astronomical Society in 1851....
on April 12, 1849, in Naples
Naples
Naples is a city in Southern Italy, situated on the country's west coast by the Gulf of Naples. Lying between two notable volcanic regions, Mount Vesuvius and the Phlegraean Fields, it is the capital of the region of Campania and of the province of Naples...
, Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
. It was the first of his nine asteroid discoveries. The director of the Naples observatory, Ernesto Capocci, named the asteroid. He chose to call it Igea Borbonica ("Bourbon
House of Bourbon
The House of Bourbon is a European royal house, a branch of the Capetian dynasty . Bourbon kings first ruled Navarre and France in the 16th century. By the 18th century, members of the Bourbon dynasty also held thrones in Spain, Naples, Sicily, and Parma...
Hygieia") in honor of the ruling family of the Kingdom of the Two Sicilies where Naples was located.
However, in 1852, John Russell Hind
John Russell Hind
John Russell Hind FRS was an English astronomer.- Life and work :John Russell Hind was born in 1823 in Nottingham, the son of lace manufacturer John Hind, and was educated at Nottingham High School...
wrote that "it is universally termed Hygeia, the unnecessary appendage 'Borbonica' being dropped." The name comes from Hygieia
Hygieia
In Greek and Roman mythology, Hygieia , was a daughter of the god of medicine, Asclepius. She was the goddess/personification of health , cleanliness and sanitation. She also played an important part in her father's cult...
, the Greek goddess
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...
of health, daughter of Asclepius
Asclepius
Asclepius is the God of Medicine and Healing in ancient Greek religion. Asclepius represents the healing aspect of the medical arts; his daughters are Hygieia , Iaso , Aceso , Aglæa/Ægle , and Panacea...
(Aesculapius for the Romans). The name was often spelled Hygeia in the nineteenth century, for example in the Monthly Notices of the Royal Astronomical Society.
Physical characteristics
Carbonate
In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....
material similar to the chondrite
Chondrite
Chondrites are stony meteorites that have not been modified due to melting or differentiation of the parent body. They formed when various types of dust and small grains that were present in the early solar system accreted to form primitive asteroids...
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. Aqueous alteration products have been detected on its surface, which could indicate the presence of water ice in the past which was heated sufficiently to melt. The primitive present surface composition would indicate that Hygiea had not been melted during the early period of Solar system formation, in contrast to other large planetesimal
Planetesimal
Planetesimals are solid objects thought to exist in protoplanetary disks and in debris disks.A widely accepted theory of planet formation, the so-called planetesimal hypothesis of Viktor Safronov, states that planets form out of cosmic dust grains that collide and stick to form larger and larger...
s like 4 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....
.
It is the main member of the Hygiea family
Hygiea family
The Hygiea family of asteroids is a grouping of dark, carbonaceous C-type and B-type asteroids in outer main belt, the largest member of which is 10 Hygiea. About 1% of all known main belt asteroids belong to this family.-Characteristics:...
and contains almost all the mass in this family (well over 90%). It is the largest of the class of dark 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...
s with a 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....
surface that are dominant in the outer asteroid 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...
—which lie beyond the Kirkwood gap
Kirkwood gap
A 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 2.82 AU. Hygiea appears to have a noticeably oblate spheroid shape, with an average diameter of 444 ± 35 km and a semimajor axis ratio of 1.11. This is much more than for the other objects in the "big four"—the dwarf planet
Dwarf planet
A dwarf planet, as defined by the International Astronomical Union , is a celestial body orbiting the Sun that is massive enough to be spherical as a result of its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite...
Ceres and the asteroids 2 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%...
and 4 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....
. Aside from being the smallest of the four, Hygiea, like Ceres, has a relatively low density, which is more comparable to the icy satellites of 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,...
or Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
than to the terrestrial planet
Terrestrial planet
A terrestrial planet, telluric planet or rocky planet is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets are the inner planets closest to the Sun...
s or the stony asteroids.
While it is the largest body in its region, due to its dark surface and larger-than-average distance from the Sun it appears very dim when observed from Earth. In fact, it is the third dimmest of the first twenty-three asteroids discovered, only 13 Egeria
13 Egeria
13 Egeria is a large main-belt G-type asteroid.It was discovered by A. de Gasparis on November 2, 1850, and was named by Urbain J. J. Le Verrier, whose computations led to the discovery of Neptune. Egeria was a goddess of Aricia, in Italy, and the wife of Numa Pompilius, second king of...
and 17 Thetis
17 Thetis
17 Thetis is a large main-belt asteroid. It is an S-type asteroid, therefore giving it a relatively bright silicate surface.It was discovered by R. Luther on April 17, 1852. It was his first asteroid discovery. Its name comes from Thetis, the mother of Achilles in Greek mythology.One Thetidian...
having lower mean opposition magnitude
Magnitude (astronomy)
Magnitude is the logarithmic measure of the brightness of an object, in astronomy, measured in a specific wavelength or passband, usually in optical or near-infrared wavelengths.-Background:...
s. At most oppositions, Hygiea has a 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...
of around +10.2, which is as much as four orders fainter than Vesta, and will require at least a 4 inches (101.6 mm) telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
to resolve. At a perihelic opposition, however, Hygiea can reach +9.1 and may just be resolvable with 10x50 binoculars
Binoculars
Binoculars, field glasses or binocular telescopes are a pair of identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes when viewing distant objects...
, unlike the next two largest asteroids in the asteroid belt, 704 Interamnia
704 Interamnia
704 Interamnia is a very large asteroid, with an estimated diameter of 350 kilometres. Its mean distance from the Sun is 3.067 . It was discovered on October 2, 1910 by Vincenzo Cerulli, and named after the Latin name for Teramo, Italy, where Cerulli worked...
and 511 Davida
511 Davida
511 Davida is a large main-belt C-type asteroid. It was discovered by R. S. Dugan in 1903. It is one of the ten most massive asteroids. It is approximately 270–310 km in diameter and comprises an estimated 1.5% of the total mass of the asteroid belt...
, which are always beyond binocular visibility.
At least 5 stellar
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...
occultation
Occultation
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...
s by Hygiea were tracked by Earth-based observers, but all with few observing independent measurements so that much was not learned of its shape. The Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
was able to resolve the asteroid, and to rule out the presence of any orbiting companions larger than about 16 km in diameter.
Orbit and rotation
Generally Hygiea's properties are the most poorly known out of the "big four" objects in the asteroid belt. Its orbit is much closer to the plane of the eclipticEcliptic
The ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...
than those of Ceres, Pallas or Interamnia, but is less circular than Ceres or Vesta with an eccentricity of around 12%. Its perihelion
Apsis
An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...
is at a quite similar longitude to those of Vesta and Ceres, though its ascending and descending nodes are opposite to the corresponding ones for those objects. Although its perihelion is extremely close to the mean distance of Ceres and Pallas, a collision between Hygiea and its larger companions is impossible because at that distance they are always on opposite sides of the ecliptic. Though in 2056, Hygiea will pass 0.025AU from Ceres, and then in 2063, Hygiea will pass 0.020AU from Pallas. At aphelion
Apsis
An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...
Hygiea reaches out to the extreme edge of the asteroid belt at the perihelia of the Hilda family
Hilda family
The Hilda asteroids consists of asteroids with a semi-major axis between 3.7 AU and 4.2 AU, an eccentricity less than 0.3, and an inclination less than 20°. They do not form a true asteroid family, in the sense that they do not descend from a common parent object. Instead, this is a dynamical...
which is in 3:2 resonance with Jupiter.
It is an unusually slow rotator, taking 27 hours and 37 minutes for a revolution, whereas 6 to 12 hours are more typical for large asteroids. Its direction of rotation is not certain at present, due to a twofold ambiguity in lightcurve data that is exacerbated by its long rotation period—which makes single-night telescope observations span at best only a fraction of a full rotation—but it is believed to be retrograde
Retrograde
-Retrograde:* Retrograde motion, in astronomy, describes retrograde motions of celestial bodies relative to a gravitationally central object* Apparent retrograde motion, in astronomy, is the apparent motion of planets as observed from a particular vantage point...
. Lightcurve analysis indicates that Hygiea's pole points towards either ecliptic coordinates
Ecliptic 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) = (30°, 115°) or (30°, 300°) 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 about 60° in both cases.
External links
- Shape model deduced from lightcurve
- A simulation of the orbit of Hygiea
- Asteroid Database—Detailed View—10 Hygiea — Horizons can be used to obtain a current ephemeris. (displays Elong from Sun and V magApparent magnitudeThe 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...
for 2011)