135 Hertha
Encyclopedia
135 Hertha is a large main-belt
asteroid
. Named Hertha
, another name for Nerthus, a Germanic fertility goddess. It orbits among the Nysa
asteroid family but its classification as an M-type asteroid
does not match the more common F-type asteroid
for this family, suggesting that it may be an interloper. Spectroscopic analysis indicates the possible presence of hydrated silicate
s indicating that 135 Hertha should possibly be reclassified from its present M-type to the proposed W-type.
Lightcurve data from Hertha indicates a flattened body, and radar
observations indicate that Hertha is non-metallic. One occultation
of a star
by the asteroid has been observed, in 2000.
on February 18, 1874, in Clinton, New York
. Further observations were carried out in 1883 by W. T. Sampson
and communicated to Astronomische Nachrichten
on his behalf by Rear Admiral R. W. Shufeldt.
reported observations of Hertha's brightness indicating a variation of half a magnitude and a short period.
In October 1992 Dotto et al. performed 20 hours of observations spread over 6 nights to investigate 135 Hertha's rotational period, approximate shape, and the coordinates of its rotational axis. They were able to confirm a rotational period of 8.398 ± .001 hours as previously measured by Harris et al. published earlier in 1992. In the same study, Dotto et al. measured the asteroid's shape and rotational axis. The axes' ratios were found to be: a/b = 1.34 ± .03 and b/c = 1.22 ± .05. Two possible values were determined for the rotational axis, however further measurements at different ecliptic longitudes are required to determine which is correct.
In August 2003 Torppa et al. published their results on the shape and rotational properties of a number of asteroids, including 135 Hertha. Utilizing data from 42 lightcurves of 135 Hertha spanning from 1978 to 2002, a more refined set of axes' ratios was obtained and a detailed shape model was obtained through inversion. New values for the axes' ratios are: a/b = 1.1 and b/c = 1.5. Measurements of the pole direction were also obtained, however like Dotto et al. they were unable to differentiate between their two possible solutions of (β=+58°, λ=96°) and (β=+53° , λ=274°).
have raised the possibility of reclassification. The presence of a dip in the observed spectrum at 3 μm indicates that the surface is hydrated, suggesting that 135 Hertha should be reclassified as a W-type (a "wet M-type") asteroid. Based on work carried out by Salisbury and Walter, the Rivkin study estimated the water content of the asteroid to be between 0.14 and 0.27 percent by mass; it should be noted, however, that this estimate is based on laboratory measurements and may not be applicable to asteroids in space.
A more recent study by Rivkin et al. published in 2002 examined the dependence of spectral absorption on the asteroid's rotational phase. The study looked at the 0.7 μm band, which is also associated with hydrated silicates, and found that the reflectance changes as the asteroid rotates, suggesting that the surface is heterogeneous with some hydrated areas intermixed with dry areas.
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...
. Named Hertha
Hertha
Hertha can be:*Another name for Nerthus, a Germanic fertility goddess*135 Hertha, an asteroid*Hertha BSC, a German football club*Hertha Zehlendorf, a German football club*CFC Hertha 06, a German sports club...
, another name for Nerthus, a Germanic fertility goddess. It orbits among the Nysa
Nysa family
The Nysa or Nysian asteroids are a group of asteroids in the Main Belt orbiting the sun between 2.41 and 2.5 AU. Asteroids in this family have eccentricities between 0.12 and 0.21 and inclinations of 1.4 to 4.3...
asteroid family but its classification as an M-type asteroid
M-type asteroid
M-type asteroids are asteroids of partially known composition; they are moderately bright . Some, but not all, are made of nickel-iron, either pure or mixed with small amounts of stone. These are thought to be pieces of the metallic core of differentiated asteroids that were fragmented by impacts,...
does not match the more common F-type asteroid
F-type asteroid
F-type asteroids are a relatively uncommon type of carbonaceous asteroid, falling into the wider C-group.-Characteristics:Generally similar to the B-type asteroids, but...
for this family, suggesting that it may be an interloper. Spectroscopic analysis indicates the possible presence of hydrated 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...
s indicating that 135 Hertha should possibly be reclassified from its present M-type to the proposed W-type.
Lightcurve data from Hertha indicates a flattened body, and radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
observations indicate that Hertha is non-metallic. One 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...
of a 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...
by the asteroid has been observed, in 2000.
Discovery
Hertha was discovered by C. H. F. PetersChristian Heinrich Friedrich Peters
Christian Heinrich Friedrich Peters was a German-American astronomer, and one of the first to discover asteroids....
on February 18, 1874, in Clinton, New York
Clinton, Oneida County, New York
Clinton is a village in Oneida County, New York, United States. The population was 1,952 at the 2000 census. It was named for George Clinton, a royal governor of the colony of New York....
. Further observations were carried out in 1883 by W. T. Sampson
William T. Sampson
William Thomas Sampson was a United States Navy rear admiral known for his victory in the Battle of Santiago de Cuba during the Spanish-American War.-Biography:...
and communicated to Astronomische Nachrichten
Astronomische Nachrichten
Astronomische Nachrichten , one of the first international journals in the field of astronomy, was founded in 1821 by the German astronomer Heinrich Christian Schumacher. It claims to be the oldest astronomical journal in the world that is still being published...
on his behalf by Rear Admiral R. W. Shufeldt.
Physical properties
After its discovery in 1874 and subsequent observations in 1884 had established Hertha's orbit, astronomers began investigation of its physical properties. As early as 1904 G. W. HillGeorge William Hill
George William Hill , was an American astronomer and mathematician.Hill was born in New York City, New York to painter and engraver John William Hill. and Catherine Smith Hill. He moved to West Nyack with his family when he was eight years old. After attending high school, Hill graduated from...
reported observations of Hertha's brightness indicating a variation of half a magnitude and a short period.
In October 1992 Dotto et al. performed 20 hours of observations spread over 6 nights to investigate 135 Hertha's rotational period, approximate shape, and the coordinates of its rotational axis. They were able to confirm a rotational period of 8.398 ± .001 hours as previously measured by Harris et al. published earlier in 1992. In the same study, Dotto et al. measured the asteroid's shape and rotational axis. The axes' ratios were found to be: a/b = 1.34 ± .03 and b/c = 1.22 ± .05. Two possible values were determined for the rotational axis, however further measurements at different ecliptic longitudes are required to determine which is correct.
In August 2003 Torppa et al. published their results on the shape and rotational properties of a number of asteroids, including 135 Hertha. Utilizing data from 42 lightcurves of 135 Hertha spanning from 1978 to 2002, a more refined set of axes' ratios was obtained and a detailed shape model was obtained through inversion. New values for the axes' ratios are: a/b = 1.1 and b/c = 1.5. Measurements of the pole direction were also obtained, however like Dotto et al. they were unable to differentiate between their two possible solutions of (β=+58°, λ=96°) and (β=+53° , λ=274°).
Spectral classification
Although 135 Hertha has long been classified as an M-type asteroid based on its spectral properties, observations carried out by Rivkin et al. in 1996 using the IRTF at Mauna Kea ObservatoryMauna Kea Observatory
The Observatories at Mauna Kea, , are an independent collection of astronomical research facilities located on the summit of Mauna Kea on the Big Island of Hawai'i, USA. The facilities are located in a special land use zone known as the "Astronomy Precinct," which is located in the Mauna Kea...
have raised the possibility of reclassification. The presence of a dip in the observed spectrum at 3 μm indicates that the surface is hydrated, suggesting that 135 Hertha should be reclassified as a W-type (a "wet M-type") asteroid. Based on work carried out by Salisbury and Walter, the Rivkin study estimated the water content of the asteroid to be between 0.14 and 0.27 percent by mass; it should be noted, however, that this estimate is based on laboratory measurements and may not be applicable to asteroids in space.
A more recent study by Rivkin et al. published in 2002 examined the dependence of spectral absorption on the asteroid's rotational phase. The study looked at the 0.7 μm band, which is also associated with hydrated silicates, and found that the reflectance changes as the asteroid rotates, suggesting that the surface is heterogeneous with some hydrated areas intermixed with dry areas.
External links
- JPL data sets for object 135 Hertha
- MPC ephemeris for 135 Hertha