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Lessons from 21 Lutetia

Lessons from 21 Lutetia. M.A. Barucci LESIA - Observatoire de Paris. ESA Rosetta mission. Journey to comet Churyumov-Gerasimenko. First rendezvous to a comet, ambitious ESA mission, cornerstone aimed at the deciphering of our origins. Comet RdV maneuver : 2014/05

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Lessons from 21 Lutetia

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  1. Lessonsfrom 21 Lutetia M.A. Barucci LESIA - Observatoire de Paris

  2. ESA Rosetta mission Journey to comet Churyumov-Gerasimenko • First rendezvous to a comet, ambitious ESA mission, cornerstone aimed at the deciphering of our origins • CometRdVmaneuver : 2014/05 • Insertion intocometorbit : 2014/09 • Lander : 2014/11 • Mission end : 2015/12 • Stein flyby: 2008/9/5 • Lutetiaflyby: 2010/7/10 Launch by Ariane 5G+ March, 2nd, 2004

  3. 500.000 km -9:30h 400.000 km -7:30h 215.000 km -4:00h 300.000 km –5:30h 81.000 km -1:30h 160.000 km -3:00h 40.000 km -0:46h 63.000 km -1:10h

  4. Is (21) Lutetia a C-type or M-type asteroid? Spectrum: Moderatelyredslope (0.3-0.75 m), generally flat (0.75-2.5 m), possible absorption band at 3 m. Albedo = 0.16-0.22 (Barucci et al. 2005, A&A 430, 313)

  5. OSIRIS data

  6. V albedo = 0.19±0.01

  7. Opposition Images 26.000 km -0:30h 20.000 km -0:22h 17.000 km -0:19h 16.000 km -0:18h α = 4.1° α = 2.0° α = 0.6°α = 0.15°

  8. (Sierks et al. 2011)

  9. Surface age: 100 Ma-3.6Ga by S. Marchi (OCA)

  10. grooves Matteo Massironi, UPD

  11. Fascinating area with multiple cross-cutting and incising of craters Cut the groove-like structure - depressions A

  12. Regolith Thickness • First estimation of d/D for different "old" regions between 0.13 and 0.3, similar to what has been measured on other planetary surfaces. • "Young" region shows craters completely buried under the regolith blanket. • If the region was similar to the rest of the asteroid before the resurfacing, these craters must be at least 600m deep, which gives a lower limit on the regolith thickness. • Craterdiameter: 70 pixels ~ 4.5 km • Blanketthickness: • ~600 m (for d/D = 0.13) • Work by Jean-Baptiste Vincent, MPS

  13. Reflectance uniform within < 5% All the variation is limited to the thermal contribution above 3500nm

  14. Temperature map from VIRTIS • Thermal Inertia : I ~20-30 SI units • Thick regolith (Coradini et al. 2011)

  15. Temperature Vs Morphological Features

  16. Spectroscopy of Lutetia: VIRTIS-M • Extremely homogeneous, less than 5% variability • No obvious spectral signature No 1 µm band (pyroxenes)

  17. Spectroscopy of Lutetia: VIRTIS-H • Calibration in progress… No 3 µm band (hydrated minerals) No 3.6 µm band (C-H in organics) No 2 µm band (pyroxenes)

  18. Conclusions from VIRTIS • No spectral signature identified • • No Fe-rich pyroxene / olivine • • No hydrated minerals • • No organics • • No unexpected absorption • => Mostly matches some primitive meteorites (chondrites) • Thermal studies • • Temperature map + reflectance spectrum & variability • Max T ~ 245K • • Thermal map implies low thermal inertia (I ~20-30 SI units) • => thick regolith at surface

  19. MIRO : Microwave Instrument for Rosetta Orbiter P.I. S. Gulkis (JPL) LESIA coIs: J. Crovisier, E. Lellouch,, D. Bockelee-Morvan, T. Encrenaz, N. Biver Radio-telescope of 30 cm: 190 GHz (1,6 mm) : continuum 563 GHz (0,5 mm) : continuum + spectro • Small thermal inertia: • I ~10-30 J/(K m2 s0.5) • (comparable Moon regolith: ~25 SI) • Subsurface (depths from ~ 2 mm to ~ 2 cm) temperatures ranged from ~ 193 K on the sunlit hemisphere to ~ 60 K on the dark hemisphere.

  20. Complementary informations Herschel observed Lutetia ! O'Rourke, L. et al. SPIRE 250, 350 & 500 µm 11 jul. 2010 PACS 70, 100 & 160 µm 21 dec. 2009

  21. Inhomogeneities on the surface of 21 Lutetia (Perna, D. et al. 2010, A&A 513, 4) Aqueous altered materials ? ferric iron spin-forbidden absorptions, phyllosilicates (jarosite…)? Lazzarin et al.2006

  22. CV3 (red) CI (green) E6 (Blue) (Nudelcu et al. 2007) (Birlan et al. 2006)

  23. (Rivkin et al. 2011, Icarus) Birlan et al., 2006, A&A, 454, 677 Birlan et al. 2006 and Rivkin et al. (2000) observed the 3 micron band diagnostic of water of hydratation; new data of Birlan et al. 2010 do not confirm this detection (different observed area), new data by Rivkin et al. 2011 confirm the band. Birlan et al., 2006

  24. 21 LUTETIA: Emissivity - SPITZER CV meteorite CO3 carb. chondrite ___0-20 micron. Iron meteorite … 20-50 micron. • The Lutetia emissivity spectrum is completely different from that of the iron meteorites • Low thermal inertia: I ≤ 30 JK−1 m−2 s−1/2 , typical of main belt asteroids; Lutetia is likely covered by a thick regolith layer • Lutetia is similar to CV3 and CO3 carbonaceous chondrites, meteorites which experienced some aqueous alteration ___0-20 micron. --- 50-100 micron. CV3 carb. chondrite ___100-150 micron. --- >150 micron. Enstatite chondrites C peakat 8.3 µm (Izawa et al. 2010) (Barucci et al., 2008)

  25. Polarimetric properties of Lutetia’s surface • Lutetia’s has particular polarimetric properties as compared to all asteroids observed so far. • Large inversion angle is indicative of • small particle size and/or • high refractory material or inclusions • Only few asteroids (mainly L-type) have wider negative branch of polarization. (Belskaya et al., 2010, A&A 515, 29)

  26. COMPARISON WITH METEORITES

  27. COMPARISON WITH METEORITES

  28. Lutetia ground observations on the cilindrical projection 0.4-0.9 µm 0.8-2.5 µm 2-3.5 µm 5-38 µm Barucci et al. (2011)

  29. V albedo = 0.19±0.01

  30. o = hemispherical+ = bidirectionalmeasurements

  31. Lutetiadensity 3.40± 0.21 g/cm3(Weiss et al. 2011) • surface similar to chondrite; • apparent high density (exceeds that of most known chondrite meteorites)

  32. Kaidunmeteorite 8-µm particle from comet 81P/Wild 2. sulphide pyrrhotite, enstatite grain and fine-grained porous aggregate material with chondritic composition This Kaidun meteorite (Yemen in 1980) is a mixture of “incompatible “ materials: principal carbonaceous chondrites (CV, CI, CM, CR) and estatitechondrites (EH and EL) and other peculiar materials. Therefore, in a single particle, materials which formed in different regions in a protoplanetary disk can co-exist, which was not expected.

  33. AlmahataSittaasteroid 2008 TC3 Sudandesert

  34. Summary (21 Lutetia) • Lutetia is clearly an old object with a surface age of 3.5 Ga with a • primitive chondrite crust and a possible partial differentiation with a metallic core. • The surface is a mixture of "incompatible'' types of materials: • carbonaceous chondrite (for the majority) and enstatitechondrite (in minor percentage). • This are the consequence of impacts that are at the origin of the present composition. • We need to put together all the pieces of puzzle • Only in situ or a Lutetia sample return will allow knowing the real surface composition of this intriguing object.

  35. ENSTATITE CHONDRITES • crushed meteorites with grain sizes less than 500 µm (Gaffey 1976) • spectral feature at 0.87-0.90 µm

  36. (a) Average densities of meteorites for C type asteroids: 2.9 – 3.5 g/cm3 (b) Average densities of meteorites for S type asteroids: 3.19 – 3.40 g/cm3 (c) Average densities of aubrites2.97 – 3.27 g/cm3

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