The Rosetta Asteroid Targets M.A. Barucci LESIA Observatoire de Paris Padova, 31/01/2006 M.A. Barucci

Rosetta mission: double Asteroid flyby (V= 139 m/s) 2867 Steins --- September 5th, 2008 rel. V = 8.6 km/s 21 Lutetia --- July 10th, 2010 rel. V = 15 km/s

Asteroid 21 Lutetia SEMIMAJOR AXIS = 2.435 AU ECCENTRICITY = 0.164, INCLINATION = 3.064 DIAMETER: 96 km 109 km 130 x 104 x 74 km (IRAS) (radiometry) (radar data) It is large enough to allow the mass and bulk density Evaluation by the radio science experiment ALBEDO: 0.22±0.02 0.17±0.07 0.11 0.09 (IRAS) (radar data) (radiometry) (polarimetry) PREVIOUS TAXONOMICAL CLASSIFICATION: M (Tholen), M0 (Barucci& Tholen) , W (Rivkin) , Xk (Bus)

Asteroid 21 Lutetia Rotational period = 8.17  0.01h Pole solution: RADAR OBS. (Magri et al, 1999) prograde rotation, axis ratio: 1.26:1.15:1.0 pole: 1= 228o  11,  1= +13o  5 or 2= 48o  11,  2= +5o  5 Pole solution: LIGHTCURVES ANALYSIS (Torppa et al., 2003) prograde rotation, axis ratio: 1.4:1.2:1.0 pole: 1= 220o  11,  1= +3o  10 or 2= 39o  10,  2= +3o  10 (Torppa et al., 2003)

21 Lutetia Spectrum: Moderately red slope (0.3-0.75 m), generally flat (0.75-2.5 m), possible absorption band at 3 m. Meteorite analogs: carbonaceous chondrites

Birlan et al. 2003 IRTF obs, 30 March 2003: IR featureless spectrum. Visible spectra from Busarev (2003) and Lazzarin et al. 2004 show faint abs. features (440 and 670 nm) possibly due to hydrated silicates. Rivkin et al. (2000) observed the 3 micron band diagnostic of water of hydratation

Birlain et al. 2005

Birlain et al. 2005

Vigarano is CV meteorite: Chondrules (30%-50%), chondrite fragments, metal, sulfate grains, and magnetite and metallic iron (2-3%) - Low porosity (1-10%)

Absorption bands

21 Lutetia Polarization: The inversion angle is the largest ever observed for asteroids. Lutetia has the lower radar albedo measured for any M type class

2867 Steins SEMIMAJOR AXIS: 2.364 AU ECCENTRICITY = 0.146, INCLINATION: 9.944o DIAMETER: 17.5 - 5.5 km ALBEDO: ? (0.04-0.4) Period=6.06+/-0.05 hrs (Hicks & Bauer, 2004) Ld P=6.048 +/-0.007 hrs (Weissmann et al. 2005)

2867 Steins sharp 0.5 m band faint 0.9 m band (sulfides, troilite or oldhamite) faint 0.9 m band (iron bearing pyroxene, orthopyr. or forsterite) Type E EII type, Angelina like partial melts derived from enstatite chondrite like parent bodies. ALBEDO determination needed!!!! --- EL6 enstatite chondrite Atlanta .…entatite achondrite (aubrite) (Barucci et al., 2004)

E-type asteroid E type surface composition seems to be dominated by iron-free or iron-poor silicates as enstatite, forsterite or feldspar, and resembles the aubrite meteorites spectra. They are a small population (around 20 asteroids classifies as E type up to now) located mainly in the inner main belt) -0.5 micron band (Burbine et al, 1999; Fornasier & Lazzarin, 2001):this band is very peculiar and its origin not yet fully understood. It might be due to sulfides such as oldhamite or troilite (sulfides are known constituent of the aubrite meteorites) -0.9 and 1.8 micron bands: due to iron bearing pyroxene such as orthopyroxene or forsterite (Clark et al., 2004)

Waiting for 2008……. New Observations: VLT SPITZER To determine the albedo + To determine the rotational axis and the best shape model

Thermal observations of Steins and Lutetia at ESO Steins - VISIR at UT3 Lutetia - TIMMI2 at La Silla 3.6m N band spectrum 7.5-13.9 mm, R=160 2006-01-09

Lutetia: 2m Faulkes 2005-12-11 (3.5 h)? 2005-12-14 (2 h)? Spitzer Space Telescope (IR Spectra + Photometry): Steins - 2005-11-22 Lutetia - 2005-12-10 Light curves Steins: ESO NTT 2005-11-28 (4 h) 2006-12-22 (2 h) Lutetia: 2m Faulkes 2005-12-11 (3.5 h)? 2005-12-14 (2 h)?

Asteroid fly-by What we need: - Maximum coverage of the surface - Observations at 0 phase angle To be in agreement with the Radio science for Lutetia to determine the mass and the density

Fly-by geometry for Lutetia   The sun vector,  , is in the fly-by plane. The angles , , ,  are as follows:  = 18.9°;  = 3.7°;  = 9.6°;  = 0.5°

Nominal fly-by geometry for Steins  The sun vector  is in the fly-by plane. The angles , , ,  are as follows:  = 23.8°;  = 5.9°;  = 50.2°;  = 0.5°

Birlain et al. 2005

Physical characterisation of igneous asteroids (E-M-X type) E type surface composition seems to be dominated by iron-free or iron-poor silicates as enstatite, forsterite or feldspar, and resembles the aubrite meteorites spectra. They are a small population (around 20 asteroids classifies as E type up to now) located mainly in the inner main belt M type are probably composed of metals such as iron and nickel and presumed to be the progenitors both of differentiated meteorites such as iron meteorites and of undifferentiated meteorites like the enstatite chondrites From 1995 some absorption bands have been identified on E and M type asteroids: - 3 micron band (Rivkin et al 1995, 2000): surprising as typically due to the first overtone of H2O and to OH vibrational fundamentals on hydrated silicates if really due to hydrated silicates, E and M type object might not be all anhydrous and igneous as previously believed and the thermal scenario in the inner main belt might be revised.

Priorities for Double Asteroid Mission SWT 15th (12/2003) Rhodia Lutetia 159 m/s Luichewoo Lutetia 129 m/s Steins Lutetia 139 m/s Baetsle Izvekov 73 m/s Baetsle Fogelin 79 m/s Luichewoo Izvekov 32 m/s Rhodia Izvekov 112 m/s Rodhia Fogelin 113 m/s Steins Izvekov 77 m/s Sofala Izvekov 146 m/s Steins Fogelin 83 m/s Luichewoo Fogelin 35 m/s

Barucci et al. 2004

Barucci et al. 2004

Mission to 67P/Churyumov-Gerasimenko Launch: 2004/03/2 Earth1 2005/03 Mars 2007/03 Earth2 2007/11 Steins 2008/09 Earth3 2009/11 Lutetia 2010/06 Comet 2014/05 RDV 2015/08 (4 UA)

Hayabusa mission: -Itokawa hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh