135 Hertha

Infobox Planet
width = 25em
name = 135 Hertha
symbol =
background = #FFFFC0


caption =
discovery_ref = Cite journal | title = Observations of the Planet Hertha (135), made at the Litchfield Observatory of Hamilton College | last = Peters | first = C.A.F. | date = 1874 | journal = Astronomische Nachrichten | volume = 84 | issue = 2001 | pages = 129 | url = http://adsabs.harvard.edu/abs/1874AN.....84..129P | doi = 10.1002/asna.18740840902]
discoverer = Christian Heinrich Friedrich Peters
discovered = February 18, 1874
discovery_site = Litchfield Observatory, Clinton, New York
mp_name =
mp_category = Nysa
alt_names =
orbit_ref = JPL Small Body]
epoch = 2008-05-14 (JD 2454600.5)
aphelion = 2.9287124854 ± 4.995e-09 AU
perihelion = 1.92827931 ± 2.0509e-07 AU
semimajor = 2.4284958975 ± 4.1419e-09 AU
eccentricity = .205977942 ± 8.4222e-08
period = 3.78 ± 9.682e-09 y
avg_speed = 18.91 km/s
mean_anomaly = 16.444645 ± 2.1094e-05°
inclination = 2.3051442 ± 9.8708e-06°
asc_node = 343.84267 ± 1.901e-4°
arg_peri = 339.91983 ± 1.9113e-4°
satellites =
dimensions = 79.24 km
mass =
density =
surface_grav =
escape_velocity =
rotation = 8.40061Cite journal | title = Shapes and rotational properties of thirty asteroids from photometric data | last = Torppa | first = J. | coauthors = "et al." | date = August 2003 | journal = Icarus | volume = 164 | issue = 2 | pages = 346–383 | doi = 10.1016/S0019-1035(03)00146-5]
sidereal_day =
axial_tilt =
pole_ecliptic_lat =
pole_ecliptic_lon =
albedo = 0.1436
temp_name1 =
mean_temp_1 =
max_temp_1 =
temp_name2 =
max_temp_2 =
spectral_type = MCite journal | title = M-type Asteroids: Rotational properties of 16 Objects | last = Dotto | first = E. | coauthors = "et al." | date = October 1992 | journal = Astronomy and Astrophysics Supplement Series | volume = 95 | issue = 2 | pages = 195–211 | url = http://adsabs.harvard.edu/abs/1992A&AS...95..195D]
abs_magnitude = 8.23

135 Hertha is a large main belt asteroid. It orbits among the Nysa asteroid family however its classification as an M-type asteroid does not match the more common F-type asteroid for this clan, suggesting that it may be an interloper. [Cite journal | title = Asteroid 'clans': Super-families or multiple events? | last = Cellino | first = A. | coauthors = Vincenzo, Z. | date = October 1993 | journal = Celestial Mechanics and Dynamical Astronomy | volume = 57 | issue = 1-2 | pages = 34–37 | url = http://adsabs.harvard.edu/abs/1993CeMDA..57...37C] Spectroscopic analysis indicates the possible presence of hydrated silicates indicating that 135 Hertha should possibly be reclassified from its present M-type to the proposed W-type.Cite journal | title = The Puzzling Case of the Nysa–Polana Family | last = Cellino | first = A. | coauthors = "et al." | date = August 2001 | journal = Icarus | volume = 152 | issue = 2 | pages = 225–237 | doi = 10.1006/icar.2001.6634]

Lightcurve data from Hertha indicates a flattened body, and radar observations indicate that Hertha is non-metallic.Cite journal | title = More Results from a Long-Term Radar Survey of M-Class Asteroids | last = Shepard | first = M.K. | coauthors = "et al." | date = September 2006 | journal = Bulletin of the American Astronomical Society | volume = 38 | pages = 626 | url = http://adsabs.harvard.edu/abs/2006DPS....38.7101S] One occultation of a star by the asteroid has been observed, in 2000.

Discovery

Hertha was discovered by C. H. F. Peters 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 [http://www.arlingtoncemetery.net/rwshufeldt-usn.htm R. W. Shufeldt] . [Cite journal | title = Observations of (135) Hertha made at the Naval Observatory Washington with 9.6 inch equatorial | last = Sampson | first = W.T. | coauthors = Shufeldt, R. W. | date = 1884 | journal = Astronomische Nachrichten | volume = 107 | pages = 323 | url = http://adsabs.harvard.edu/abs/1884AN....107..323S | doi = 10.1002/asna.18841072006]

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. Hill reported observations of Hertha's brightness indicating a variation of half a magnitude and a short period.Cite journal | title = Variability of (135) Hertha | last = Hill | first = G.W. | date = March 1904 | journal = Astronomical Journal | volume = 24 | issue = 557 | pages = 42 | url = http://articles.adsabs.harvard.edu/full/1904AJ.....24...42H | doi = 10.1086/103543]

In October of 1992 Dotto "et al." performed 20 hours of observations spread over 6 nights to investigate 135 Hertha's rotational period, approximate shape, 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.Cite journal | title = Asteroid lightcurve observations from 1981 | last = Harris | first = A.W. | coauthors = "et al." | date = January 1992 | journal = Icarus | volume = 95 | issue = 1 | pages = 115–147 | doi = 10.1016/0019-1035(92)90195-D] 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 of 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°).

pectral 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 Observatory 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.Cite journal | title = The Nature of M-Class Asteroids from 3-μm Observations | last = Rivkin | first = A.S. | coauthors = "et al." | date = June 2000 | journal = Icarus | volume = 145 | issue = 2 | pages = 351–368 | doi = 10.1006/icar.2000.6354] 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.Cite journal | title = Hydrated Minerals on Asteroids: The Astronomical Record | last = Rivkin | first = A.S. | coauthors = "et al." | date = March 2002 | journal = Technical Report, Massachusetts Institute of Technology | url = http://www.lpi.usra.edu/books/AsteroidsIII/pdf/3031.pdf]

External links

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* JPL data sets for object [http://pdsproto.jpl.nasa.gov/catalog/target/Results.CFM?resultsselbox=135%20HERTHA 135 Hertha]

* IAU ephemeris for [http://cfa-www.harvard.edu/iau/Ephemerides/Bright/2008/00135.html 135 Hertha]

Further reading

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References