Ro etta at teins and toward utetia

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Marcello Fulchignoni Venezia, April 1st , 2009

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1986 1987

1988

1989

1991

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 PayloadScientific 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

1993

1996

1998

E

C

2867 Steins

21 Lutetia

2004

2867 SteinsSEMIMAJOR AXIS: 2.364 AUECCENTRICITY = 0.146INCLINATION: 9.944o

LdPeriod=6.06+/-0.05 hrs(Hicks & Bauer, 2004)

P=6.048 +/-0.007 hrs(Weissmann et al. 2005)

SHAPE & POLE OF STEINSLamy et al., 2008

λ1 = 250° ± 5° β1 = - 89° ± 5°

Shape: Pole coordinates:

a=5.73 kmb=4.95 kmc=4.58 km

Light Curve and Modelled Shape

Distance to Steins 12 Mio. km on 20. Aug. 2008 Shape 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 likepartial 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 SteinsPolarimetric results on 2867 Steins

Polarimetric properties are consistent with high Polarimetric properties are consistent with high albedo E-type asteroidsalbedo E-type asteroids

Tx slope inv

Steins 0.037 17.3 Steins 0.037 17.3

E 0.04 17.8E 0.04 17.8

S 0.09 20.1S 0.09 20.1

M 0.09 23.5M 0.09 23.5

C 0.28 20.5C 0.28 20.5

Albedo = 0.45Albedo = 0.450.10.1

(Fornasier et al., 2006)

SPITZER DATA OF 2867 STEINS SPITZER DATA OF 2867 STEINS

Lamy et al. (2008) A=0.34 ± 0.06

SPITZER DATA OFSPITZER DATA OF 2867 STEINS (PI P. Lamy)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: DSpitzer = 1.60A Phase =27.2° DSun= 2.130 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 STEINSSPITZER DATA OF 2867 STEINS

Steins emissivity spectrum is very similar to that of the aubrite meteoritesaubrite meteorites (enstatite achondrites, which have the E-type asteroids as parent bodies) and of the enstatite mineralenstatite mineral

(Barucci et al., 2008)

Enstatite chondrites

Steins Fly-by OverviewSteins Fly-by Overview

4 August 2008 to 3 October 2008Closest approach:5 Sept. 2008 18:58

rH = 2.14 AU, Δ = 2.41 AURelative velocity: 8.62 km/sTargeted 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/px5Sept 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 ( 0.25-5 micron)

spatial resolution is ~ 300 m/pix

Temperature (left)and emissivity( right) Maps for ε =1

200 230

Temps après l'approche maxi ->

Fro

id

C

hau

d

Fro

id

C

hau

d

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 km 53 km 31 km 17 km 0.35 km 6.7 x 5.9 x 4.3 km

Period 7.09 hr 17.406 d 4.634 hr 5.267 hr 12.132 hr 6.047 hr

Age 200 My 2-4.5 Gy 1 Gy 2 Gy 1-100 My 100-150 My

Density 2.7g/cm3 (b) 1.3 g/cm3 (a) 2.6 g/cm3 (b) 2.67 g/cm3

(b)1.95 g/cm3 (b) ? ( c )

Porosity ? 55 – 63 % 18 – 24 % 16 – 21 % 39 – 43 % ?

Meteorite ordinarychondrite

carbonaceous chondrite

ordinary chondrite

ordinary chondrite

ordinary chondrite

aubrite

Objective Fly-By Galileo (1991) Res=54m/px

Fly-by NEAR (1997)

Res=180m/px

Fly-byGalileo (1993)Res=25m/px

1 year-RDNEAR (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 = 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 determination

• by the radio science experiment

• ALBEDO: 0.22±0.02 0.17±0.07 0.11 0.09

• (IRAS) (radar data) (radiometry) (polarimetry)

• D= 98.3 ± 5.9 km A=0.208 ± 0.025 (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 LutetiaRotational 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

Shape and 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

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

Aqueous altered materials ?

ferric iron spin-forbidden absorptionphyllosilicates (jarosite…)

oxidised iron

Lazzarin et al. 2004

Birlan et al. 2006 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 valueA=0.208 ± 0.025 D= 98.3 ± 5.9 km

21 LUTETIA21 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