135 Hertha
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Hertha (
minor planet designation A formal minor-planet designation is, in its final form, a number–name combination given to a minor planet (asteroid, centaur, trans-Neptunian object and dwarf planet but not comet). Such designation always features a leading number (catalog o ...
: 135 Hertha) is an
asteroid An asteroid is a minor planet of the Solar System#Inner solar system, inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic o ...
from the inner region of the
asteroid belt The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, called ...
, approximately in diameter. Discovered on 18 February 1874 by German–American astronomer
Christian Peters Christian Heinrich Friedrich Peters (September 19, 1813 – July 18, 1890) was a German–American university teacher and astronomer at the Litchfield Observatory of Hamilton College, New York, and a pioneer in the study and visual discovery of ...
at the Litchfield Observatory near Clinton, New York, it was named after the Teutonic and Scandinavian goddess of fertility, Hertha, also known as
Nerthus In Germanic paganism, Nerthus is a goddess associated with a ceremonial wagon procession. Nerthus is attested by first century AD Roman historian Tacitus in his ethnographic work ''Germania''. In ''Germania'', Tacitus records that a group of Germ ...
. It orbits among the Nysa asteroid family, but its classification as a metallic M-type asteroid does not match the more common F-type asteroid for this family, suggesting that it may be an
interloper Interloper, Interlopers or The Interlopers may refer to: Entertainment * '' The Interloper: Lee Harvey Oswald Inside the Soviet Union'', a 2013 book by Peter Savodnik * Interloper (comics), a fictional character in the Marvel Comics universe * I ...
. Spectroscopic analysis indicates the possible presence of hydrated silicates indicating that ''Hertha'' should possibly be reclassified from its present M-type to the proposed W-type.
Lightcurve In astronomy, a light curve is a graph of light intensity of a celestial object or region as a function of time, typically with the magnitude of light received on the y axis and with time on the x axis. The light is usually in a particular frequ ...
data from ''Hertha'' indicates a flattened body, and
radar Radar is a detection system that uses radio waves to determine the distance ('' ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
observations indicate that ''Hertha'' is non-metallic. Five
occultation An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks ...
s of
star A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth make ...
s by the asteroid have been observed between 2000 and 2015.


Discovery

''Hertha'' was discovered by
C. H. F. Peters Christian Heinrich Friedrich Peters (September 19, 1813 – July 18, 1890) was a German–American university teacher and astronomer at the Litchfield Observatory of Hamilton College, New York, and a pioneer in the study and visual discovery of ...
on 18 February 1874, in Clinton, New York. Further observations were carried out in 1883 by W. T. Sampson and communicated to
Astronomische Nachrichten ''Astronomische Nachrichten'' (''Astronomical Notes''), one of the first international journals in the field of astronomy, was established in 1821 by the German astronomer Heinrich Christian Schumacher. It claims to be the oldest astronomical jou ...
on his behalf by Rear Admira
R. W. Shufeldt


Physical properties

After its discovery in 1874, subsequent observations in 1884 established ''Hertha'' orbit. Astronomers then began investigation of its physical properties. As early as 1904, G. W. Hill reported observations of ''Hertha'' 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 ''Hertha'' 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 longitude The ecliptic coordinate system is a celestial coordinate system commonly used for representing the apparent positions, orbits, and pole orientations of Solar System objects. Because most planets (except Mercury) and many small Solar System b ...
s 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 ''Hertha''. Utilizing data from 42 lightcurves of ''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°). In 2017, Hanuš ''et al.'' confirmed that the correct solution is β=°, λ=°. They also calculated the first non-convex shape model, based on lightcurve and stellar occultation data.


Spectral classification

Although ''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 Observatory The Mauna Kea Observatories (MKO) are a group of independent astronomical research facilities and large telescope observatories that are located at the summit of Mauna Kea on the Big Island of Hawaiʻi, United States. The facilities are located ...
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 ''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. 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 family

''Hertha'' is one of the core members of the Nysa family ( 405) also known as Herta family. The Nysa–Polana complex is the main-belt's largest grouping of asteroids with nearly 20,000 members.


Further reading

* *


References


External links


Lightcurve plot of 135 Hertha
Palmer Divide Observatory, '' B. D. Warner'' (2008)
2008-Dec-11 Occultation



Asteroid Lightcurve Database (LCDB)
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Dictionary of Minor Planet Names
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– Observatoire de Genève, Raoul Behrend

– Minor Planet Center * * {{DEFAULTSORT:Hertha 000135 Discoveries by Christian Peters Named minor planets 000135 000135 000135 18740218