21 Lutetia

21 Lutetia

Infobox Planet | discovery=yes | physical_characteristics = yes | bgcolour=#FFFFC0
name=21 Lutetia
discoverer=Hermann M. S. Goldschmidt
discovered=November 15, 1852
mp_category=Main belt
epoch=January 30, 2005 (JD 2453400.5)
semimajor=364.277 Gm (2.435 AU)
perihelion=304.600 Gm (2.036 AU)
aphelion=423.955 Gm (2.834 AU)
period=1387.902 d (3.80 a)
avg_speed=18.96 km/s
dimensions=120×100×80 km [http://www.psi.edu/pds/archive/astdata04/simps04/diamalb.tab Supplemental IRAS Minor Planet Survey] ] cite journal | author= J. Torppa et al.| title= "Shapes and rotational properties of thirty asteroids from photometric data"| journal= Icarus| year= 2003| volume= 164| pages= 346| url= http://www.rni.helsinki.fi/~mjk/thirty.pdf| doi= 10.1016/S0019-1035(03)00146-5] cite journal | author= M. Mueller et al.| title= "The size and albedo of Rosetta fly-by target 21 Lutetia from new IRTF measurements and thermal modeling"| journal= Astronomy & Astrophysics| year= 2006| volume= 447| pages= 1153| url= http://www.edpsciences.org/articles/aa/pdf/2006/09/aa3742-05.pdf?access=ok| doi= 10.1051/0004-6361:20053742]
density=~2.7 g/cm³ cite journal | author= G. A. Krasinsky et al.| title= "Hidden Mass in the Asteroid Belt"| journal= Icarus| year= 2002| volume= 158| pages= 98| doi= 10.1006/icar.2002.6837]
surface_grav=~0.025 m/s²
escape_velocity=~0.05 km/s
rotation=0.3402 d (8.165 h) [http://www.psi.edu/pds/archive/lc.html PDS lightcurve data] ]
spectral_type=M [http://www.psi.edu//pds/resource/taxonomy.html PDS spectral class data] ]
magnitude = 9.24 (brightest)
abs_magnitude=7.29 cite journal | author= C. Magri et al.| title= "Mainbelt Asteroids: Results of Arecibo and Goldstone Radar Observations of 37 Objects during 1980-1995"| journal= Icarus| year= 1999| volume= 140| pages= 379| url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999Icar..140..379M&db_key=AST&data_type=HTML&format=&high=444b66a47d20870| doi= 10.1006/icar.1999.6130 ]
single_temperature=~172 K
"max:" 266 K (-7 °C)

21 Lutetia (pronEng|ljuˈtiːʃiə, _la. Lutētia) is a large Main belt asteroid of the M spectral type, about 100 kilometers in diameter. It will be the subject of a flyby by the "Rosetta" space probe in 2010.

The name Lutetia derives from the Latin name for Paris.


The composition of Lutetia has puzzled astronomers for some time, and its investigation has picked up in recent years in anticipation of the upcoming "Rosetta" flyby. While classified as the M spectral type, it is one of the anomalous members which do not display much evidence of metal on their surface. In fact, there are various indications of a non-metallic surface: A flat low frequency spectrum similar to that of carbonaceous chondrites and C-type asteroids,cite journal | author= Birlan, M., et al.| title= "Near-IR spectroscopy of asteroids 21 Lutetia, 89 Julia, 140 Siwa, 2181 Fogelin and 5480 (1989YK8) " [sic ] ", potential targets for the Rosetta mission; remote observations campaign on IRTF"| journal= New Astronomy| year= 2004| volume= 9| pages= 343| url= http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004NewA....9..343B&db_key=AST&data_type=HTML&format=&high=444b66a47d20870| doi= 10.1016/j.newast.2003.12.005] and not at all like that of metallic meteorites, a low radar albedo whereas strongly metallic asteroids like e.g. 16 Psyche have a high one, evidence of hydrated materials on its surface,cite journal | author= M. Lazzarin et al.| title= "Visible spectral properties of asteroid 21 Lutetia, target of Rosetta Mission"| journal= Astronomy and Astrophysics| year= 2004| volume= 425| pages= L25| url= http://www.edpsciences.org/articles/aa/pdf/2004/38/aagf171.pdf?access=ok| doi= 10.1051/0004-6361:200400054] abundant silicates,cite journal | author= M. A. Feierberg et al.| title= "Detection of silicate emission features in the 8- to 13 micrometre spectra of main belt asteroids"| journal= Icarus| year= 1983| volume= 56| pages= 393| url= http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1983Icar...56..393F&db_key=AST&data_type=HTML&format=&high=444b66a47d20870| doi= 10.1016/0019-1035(83)90160-4] and a thicker regolith than most asteroids.cite journal | author= A. Dollfus & J. E. Geake| title= "Polarimetric properties of the lunar surface and its interpretation. VII - Other solar system objects"| journal= Proceedings of the 6th Lunar Science Conference, Houston, Texas, March 17-21 | year= 1975| volume= 3| pages= 2749| url= http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1975LPSC....6.2749D&link_type=ARTICLE&db_key=AST]

Lightcurve analysis indicates that Lutetia's pole points towards either ecliptic coordinates (β, λ) = (3°, 40°) or (β, λ) = (3°, 220°) with a 10° uncertainty.cite journal | author= J. Torppa et al.| title= "Shapes and rotational properties of thirty asteroids from photometric data"| journal= Icarus| year= 2003| volume= 164| pages= 346| url= http://www.rni.helsinki.fi/~mjk/thirty.pdf | doi= 10.1016/S0019-1035(03)00146-5] This gives an axial tilt of 85°, or 89°, respectively, meaning that Lutetia spins at an approximately right angle to the ecliptic like e.g. Uranus.


Lutetia was discovered on November 15, 1852 by Hermann Mayer Salomon Goldschmidt from the balcony of his apartment in Paris.

On July 10, 2010, the European "Rosetta" comet probe will pass the asteroid with a minimum distance of 3000 km and a velocity of 15 kilometres per second on its way to 67P/Churyumov-Gerasimenko. [cite journal
title = Rosetta Asteroid Targets: 2867 Steins and 21 Lutetia
author = M. A. Barucci, M. Fulchignoni and A. Rossi
journal = Space Science Reviews
volume = 128
issue = 1-4
pages = 67–78
year = 2007
url =
doi = 10.1007/s11214-006-9029-6
] In the run-up to this event the attention of astronomers has been drawn to Lutetia.

The flyby will be important for the understanding of the asteroids, since Lutetia will be the first M-type asteroid to be visited by a spacecraft.

There have been two reported stellar occultations by Lutetia: from Malta (1997) and Australia (2003), with only one chord each, roughly agreeing with IRAS measurements.


External links

* [http://www.rni.helsinki.fi/~mjk/thirty.pdf shape model deduced from lightcurve]
* [http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=21;orb=1 Orbital simulation] from JPL (Java) / [http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=sb&sstr=21 Ephemeris]

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