Techniques d'observation spectroscopique d'astéroïdes
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Techniques d'observation spectroscopique d'astéroïdes

Techniques d'observation spectroscopique d'astéroïdes Techniques d'observation spectroscopique d'astéroïdes

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22.01.2014 Views

118 CHAPTER 7. SPECTRAL PROPERTIES OF MAIN BELT ASTEROIDS spectrum of 9147 Kourakuen is almost identical with the spectrum of a sample from Pavlovka meteorite (Fig. 7.1c). This meteorite sample is of type achondrite howardite already studied so far [Olsen et al., 1990, Labotka & Papike, 1980]. The bulk composition of the chondrules from this meteorite contains SiO 2 (50.1%), MgO(23.7%), FeO(15%), Al 2 O 3 (6.2%), CaO(3.8%) [Olsen et al., 1990]. Other meteorite laboratory spectra similar to the spectrum of (9147) Kourakuen are those of the meteorites Roda (Achondrite Diogenite), Le Teilleul (Achondrite, Howardite) and Kapoeta (Basaltic HED Howardite). The first fifty solutions that matched our spectrum are HED (Howardite Eucrite Diogenite) meteorites. These are basaltic meteorites believed to result from large asteroids that melted to form a metallic core and basaltic magma after the formation. tel-00785991, version 1 - 7 Feb 2013 Another solution of this application is a spectrum of a man-made mixture of Pyroxene Hypersthene Plagioclase Bytownite Ilmenite (Fig. 7.1d). This man-made mixture reproduces quite well the natural composition of volcanic rocks or melting rock of volcanic beds, and is consistent to the V-type mineralogical composition of asteroids. In all laboratory spectra proposed by M4AST to match this asteroid spectrum, the majority corresponds to HED achondrite meteorites. While the standard deviation measures the overall matching between the two spectra, the correlation coefficient finds those spectra for which the spectral features positions and shapes are very close. In the case of spectrum of (9147) Kourakuen, a very high correlation coefficient (more than 0.99) characterize the first matching solutions (Table 7.4). Since only the NIR part of the spectrum is available, we can only compute the band minima. The high signal to noise ratio of this spectrum ensures that there is a small error in computing the band minima. The first minimum is at 0.9217 ± 0.0005 µm and the second minimum is at 1.9517±0.0062 µm, which imply a band separation of 1.03 µm. The band separation provides a way of estimating the iron content. Cloutis et al. [1990] noted that the band separation is a linear function of the BII minimum for orthopyroxenes and that both parameters increase with the iron content. If we refer to the relation obtained by de Sanctis et al. [2011b], the parameters that we found match their formula y = 0.801∗x−0.536, where y is the band separation and x is the BII minimum. These parameters correspond to an iron content of around 40 wt%. However, the laboratory calibrations suggest that the correspondence is true for a number of low aluminum orthopyroxenes but invalid for mixtures of olivine, metal, and both ortho- and clino-pyroxenes [de Sanctis et al., 2011b]. Concluding this section, based on an accurate near-infrared spectrum of the asteroid (9147) Kourakuen a description of its surface composition was made. The comparisons with meteorites spectra which revealed a spectral matching with HED type meteorites (in particular with the spectrum of Pavlovka meteorite) agrees and is complementary to the taxonomical classification and to the mineralogical solution found.

CHAPTER 7. SPECTRAL PROPERTIES OF MAIN BELT ASTEROIDS 119 Table 7.4: Summary of results obtained by matching the main belt asteroids spectra with spectra from Relab database. The most relevant matches are presented. The comparison coefficients are given together with some details related to the laboratory samples. tel-00785991, version 1 - 7 Feb 2013 Spectrum std. dev. corr. coef. Meteorite/Sample Sample ID Type 9147 0.01884 0.99477 Pavlovka MR-MJG-094 Achondrite(AHOW) 0.02244 0.99207 Mixture SC-EAC-039 Man-made 0.02731 0.99048 Roda MR-MJG-099 Achondrite(ADIO) 854 0.01894 0.98847 "ALHA76005,85" MB-TXH-066-A HED Eucrite 0.01917 0.98842 "Y-793591,90" MT-TXH-043-A HED Eucrite 0.02396 0.98332 "ALH-78132,61" MB-TXH-072-A HED Eucrite 1333 0.02065 0.97005 Saratov MR-MJG-046 OC/L4 0.02248 0.97188 Hamlet #1 MR-MJG-069 OC/LL4 0.02413 0.95487 Paranaiba MB-CMP-010-D OC/L6 1333 0.01774 0.93893 Denver TB-TJM-072 OC/L6 De-reddened 0.02841 0.94397 Hamlet #1 MR-MJG-069 OC/LL4 3623 0.04344 0.83962 Gabbro 50S RG-CMP-057 Rock/Igneous Plutonic 0.04334 0.83360 14321,150P LS-JBA-097 Rock/Polymict Breccia 3623 0.03296 0.79520 Fayetteville MB-CMP-007-L OC/H4 De-reddened 0.04093 0.79900 Gabbro Ns RG-CMP-017 Rock/Igneous Plutonic 1048 0.08761 0.93656 PYX:OLV:PLG:ILM SC-EAC-045 Man - Made 0.09487 0.93345 Mixture SC-EAC-060 Man - Made 31569 0.04156 0.96088 Pasamonte MR-MJG-090 HED Eucrite 0.04112 0.95996 Mineral SB-RGB-001 Pigeonite 0.04433 0.95991 Macibini Clast 3 TB-RPB-027 HED Eucrite 7.3 A binary asteroid: (854) Frostia The number of known multiple systems among asteroids has increased significantly in recent years. In the past, the binarity and multiplicity of asteroids was suggested by several authors [van Flandern et al., 1979] based on occultations of stars (for example in the articles of Binzel [1978] 2 , and Donnison [1979] 3 ) or photometry [Tedesco, 1979, Binzel & van Flandern, 1979, Dunlap & Gehrels, 1969]. These observational facts were at the origin of theoretical problems related to spin evolution and stability [Wijesinghe & Tedesco, 1979, Zappala et al., 1980, Leone et al., 1984]. Analytical and numerical simulations of catastrophic collisions among small bodies, using several hypothesis, are published regularly by several teams [Dell’Oro & Cellino, 2007, Durda et al., 2004, Holsapple & Michel, 2008]. This topic remains open despite an important acquisition of knowledge from laboratory experiments and numerical tests. The most important conclusion of these works is that elongated shapes, binarity or multiplicity could be explained for both large objects (≈100 km in size) and relatively small ones (kilometer-size asteroids). For instance, a doublet system is a binary system where both bodies are of nearly equal sizes. Their origin is not well understood, but several such systems have been reported (ex: (90) Antiope, (617) Patroclus, (69230) Hermes, 1998 WW31). Theoretical studies concerning the 2 The article also presents historical facts of occultation of stars by asteroids. 3 This satellite was not confirmed by direct imaging. [Storrs et al., 1999]

CHAPTER 7. SPECTRAL PROPERTIES OF MAIN BELT ASTEROIDS 119<br />

Table 7.4: Summary of results obtained by matching the main belt asteroids spectra with spectra from Relab<br />

database. The most relevant matches are presented. The comparison coefficients are given together with some<br />

details related to the laboratory samples.<br />

tel-00785991, version 1 - 7 Feb 2013<br />

Spectrum std. dev. corr. coef. Meteorite/Sample Sample ID Type<br />

9147 0.01884 0.99477 Pavlovka MR-MJG-094 Achondrite(AHOW)<br />

0.02244 0.99207 Mixture SC-EAC-039 Man-made<br />

0.02731 0.99048 Roda MR-MJG-099 Achondrite(ADIO)<br />

854 0.01894 0.98847 "ALHA76005,85" MB-TXH-066-A HED Eucrite<br />

0.01917 0.98842 "Y-793591,90" MT-TXH-043-A HED Eucrite<br />

0.02396 0.98332 "ALH-78132,61" MB-TXH-072-A HED Eucrite<br />

1333 0.02065 0.97005 Saratov MR-MJG-046 OC/L4<br />

0.02248 0.97188 Hamlet #1 MR-MJG-069 OC/LL4<br />

0.02413 0.95487 Paranaiba MB-CMP-010-D OC/L6<br />

1333 0.01774 0.93893 Denver TB-TJM-072 OC/L6<br />

De-reddened 0.02841 0.94397 Hamlet #1 MR-MJG-069 OC/LL4<br />

3623 0.04344 0.83962 Gabbro 50S RG-CMP-057 Rock/Igneous Plutonic<br />

0.04334 0.83360 14321,150P LS-JBA-097 Rock/Polymict Breccia<br />

3623 0.03296 0.79520 Fayetteville MB-CMP-007-L OC/H4<br />

De-reddened 0.04093 0.79900 Gabbro Ns RG-CMP-017 Rock/Igneous Plutonic<br />

1048 0.08761 0.93656 PYX:OLV:PLG:ILM SC-EAC-045 Man - Made<br />

0.09487 0.93345 Mixture SC-EAC-060 Man - Made<br />

31569 0.04156 0.96088 Pasamonte MR-MJG-090 HED Eucrite<br />

0.04112 0.95996 Mineral SB-RGB-001 Pigeonite<br />

0.04433 0.95991 Macibini Clast 3 TB-RPB-027 HED Eucrite<br />

7.3 A binary asteroid: (854) Frostia<br />

The number of known multiple systems among asteroids has increased significantly in recent<br />

years. In the past, the binarity and multiplicity of asteroids was suggested by several authors<br />

[van Flandern et al., 1979] based on occultations of stars (for example in the articles of Binzel<br />

[1978] 2 , and Donnison [1979] 3 ) or photometry [Tedesco, 1979, Binzel & van Flandern, 1979,<br />

Dunlap & Gehrels, 1969]. These observational facts were at the origin of theoretical problems<br />

related to spin evolution and stability [Wijesinghe & Tedesco, 1979, Zappala et al., 1980,<br />

Leone et al., 1984].<br />

Analytical and numerical simulations of catastrophic collisions among small bodies, using<br />

several hypothesis, are published regularly by several teams [Dell’Oro & Cellino, 2007,<br />

Durda et al., 2004, Holsapple & Michel, 2008]. This topic remains open despite an important<br />

acquisition of knowledge from laboratory experiments and numerical tests. The most important<br />

conclusion of these works is that elongated shapes, binarity or multiplicity could be explained<br />

for both large objects (≈100 km in size) and relatively small ones (kilometer-size asteroids).<br />

For instance, a doublet system is a binary system where both bodies are of nearly equal sizes.<br />

Their origin is not well understood, but several such systems have been reported (ex: (90)<br />

Antiope, (617) Patroclus, (69230) Hermes, 1998 WW31). Theoretical studies concerning the<br />

2 The article also presents historical facts of occultation of stars by asteroids.<br />

3 This satellite was not confirmed by direct imaging. [Storrs et al., 1999]

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