Ro etta at teins and toward utetia S Marcello FulchignoniVenezia, April 1 st, 2009 L

Rosetta A Comet rendezvous Mission

11 Orbiter Instruments/ (Instrument Packages)  18 Experiments Payload Mass: ~170 kg + Lander: ~110 kg 10 Lander Instruments/ (Instrument Packages) => 16 Experiments Rosetta Scientific Payload Payload Mass: ~27 kg

Rosetta was also seen from the Earth

B S S S C 3840 Mimistrobel 2530 Shipka 2703 Rodari 4979 Otawara 140 Siwa

E C 2867 Steins 21 Lutetia 2004

2867 Steins SEMIMAJOR AXIS: AU ECCENTRICITY = INCLINATION: o Ld Period=6.06+/-0.05 hrs (Hicks & Bauer, 2004) P= / hrs (Weissmann et al. 2005)

SHAPE & POLE OF STEINS Lamy et al., 2008 λ 1 = 250° ± 5° β 1 = - 89° ± 5° Shape:Pole coordinates: a=5.73 km b=4.95 km c=4.58 km

Light Curve and Modelled Shape Distance to Steins 12 Mio. km on 20. Aug. 2008Shape model of Steins α = 33° OSIRIS Observations

2867 Steins sharp 0.5  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. --- EL6 enstatite chondrite Atlanta.…entatite achondrite (aubrite) (Barucci et al. 2005)

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 (25 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) E-type asteroid

Polarimetric results on 2867 Steins Polarimetric properties are consistent with high albedo E-type asteroids Tx slope inv Steins E S M C Albedo = 0.45  0.1 (Fornasier et al., 2006)

SPITZER DATA OF 2867 STEINS Lamy et al. (2008)A=0.34 ± 0.06

SPITZER DATA OF 2867 STEINS (PI P. Lamy) 6 hours of full coverage on 22 November 2005, with IRS, for a total of 14 spectra [5-38 micron ]. Observing conditions: D Spitzer = 1.60A Phase =27.2° D Sun = AU Emissivity spectra were obtained dividing the Spitzer spectra by the SED (calculated using the thermal model presented Lamy et al., 2008) (Barucci et al., 2008)

SPITZER DATA OF 2867 STEINS aubrite meteorites enstatite mineral Steins emissivity spectrum is very similar to that of the aubrite meteorites (enstatite achondrites, which have the E-type asteroids as parent bodies) and of the enstatite mineral (Barucci et al., 2008)

Enstatite chondrites

Steins Fly-by Overview 4 August 2008 to 3 October 2008 Closest approach: 5 Sept :58 r H = 2.14 AU, Δ = 2.41 AU Relative velocity: 8.62 km/s Targeted minimum flyby distance: 800 km

Final fly-by scenario: a complex matter S/C flip started 40 min before closest approach 20 minutes duration Phase angle coverage: 0-140° Phase angle at approach: 38.5 deg Phase angle zero at 1280 km

NAC best res. Image (100m/px) 5Sept UT: 18:28, dist:5200 km, phase=30° WAC best res. Image (80m/px) 5Sept UT: 18:38:15 dist:806km,phase=50 ° WAC res. 100 m/px 5Sept UT: 18:36:45, dist=1029 km,phase=12°

Colour images

Steins Albedo: 0.38 ± 0.05

WAC Spectrophotometry 24

Virtis H Steins Spectrum in radiance units (still relative – absolute calibration waiting for filling factor accurate estimates from final pointing)

VIRTIS-M 288 spectral bands ( micron) spatial resolution is ~ 300 m/pix

Temperature (left)and emissivity( right) Maps for ε =

Temps après l'approche maxi ->  Froid Chaud  Signal mm Signal submm Signal continuum détecté par MIRO peu après l'approche maximale à Steins le 5.78 Septembre 2008

Asteroid (Type) Gaspra (S)Mathilde (C)Ida (S)Eros (S)Itokawa (S)Steins (E) Diameter 12 km53 km31 km17 km0.35 km6.7 x 5.9 x 4.3 km Period 7.09 hr d4.634 hr5.267 hr hr6.047 hr Age 200 My2-4.5 Gy1 Gy2 Gy1-100 My My Density 2.7g/cm 3 (b)1.3 g/cm 3 (a)2.6 g/cm 3 (b)2.67 g/cm 3 (b) 1.95 g/cm 3 (b)? ( c ) Porosity ?55 – 63 %18 – 24 %16 – 21 %39 – 43 %? Meteorite ordinary chondrite carbonaceous chondrite ordinary chondrite aubrite Objective Fly-By Galileo (1991) Res=54m/px Fly-by NEAR (1997) Res=180m/px Fly-by Galileo (1993) Res=25m/px 1 year-RD NEAR (2000) Res=cm/px Hovering Hayabusa (2005) Res<1cm/px Fly-by Rosetta (2008) Res<80 m/px Science return -First asteroid with young age (200 Myr) -Absence of large craters -First asteroid with low density - Large craters (5 with D> 5 km) suggest porous bodies have much higher impact strength than expected - First discovery of a satellite (Dactyl) - Age estimate (1 Byr) - First estimate of density of S-type - First constraints on mechanical properties - Larger amount of boulders than expected - Lack of very small craters - First evidence of thick regolith - First evidence of rubble-pile structure - First S-type with low bulk density - Amount of large boulders - Lack of small craters (<10 m) requires unknown process -- First chunk of e highly differentiated object --First visit to of a body shaped by the YORP effect?

SEMIMAJOR AXIS = AU ECCENTRICITY = 0.164, INCLINATION = 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 determination by the radio science experiment ALBEDO: 0.22± ± (IRAS) (radar data) (radiometry) (polarimetry) D= 98.3 ± 5.9 km A=0.208 ± (Mueller et al. 2006) PREVIOUS TAXONOMICAL CLASSIFICATION: M (Tholen), M0 (Barucci & Tholen), W (Rivkin), Xk (Bus) Asteroid 21 Lutetia

Asteroid comparative sizes 21 Lutetia 2867 Steins

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 = 228 o  11,  1 = +13 o  5 or 2 = 48 o  11,  2 = +5 o  5 Shape and pole solution: LIGHTCURVES ANALYSIS (Torppa et al., 2003) prograde rotation, axis ratio: 1.4:1.2:1.0 pole: 1 = 220 o  11,  1 = +3 o  10 or 2 = 39 o  10,  2 = +3 o  10

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

Aqueous altered materials ? ferric iron spin-forbidden absorption phyllosilicates (jarosite…) oxidised iron Lazzarin et al. 2004

Birlan et al and Rivkin et al. (2000) observed the 3 micron band diagnostic of water of hydratation

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

8 hours of full coverage on 10 December 2005 with IRS, for a total of 14 spectra [5-38 micron]. 21 LUTETIA SPITZER DATA 21 LUTETIA SPITZER DATA

21 Lutetia the STM applied to Spitzer data gives albedo = 0.18 beam. factor=1.49 Also Mueller et al. (2006) with ground based thermal observations determined a similar albedo value A=0.208 ± D= 98.3 ± 5.9 km

21 LUTETIA The Lutetia emissivity spectrum is completely different from that of the iron meteorites, so the possible metallic nature for Lutetia is rejected! Lutetia is similar to CV3 and CO3 carbonaceous chondrites, meteorites which experienced some aqueous alteration

THE END RdV : 21 Lutetia 10 July 2010