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I. Abstract Infrared Spectra of Asteroid 243 Ida and Its Satellite Dactyl Have

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I. Abstract Infrared Spectra of Asteroid 243 Ida and Its Satellite Dactyl Have #1045 A Comparison of Ordinary Chondrites With 243 Ida and Dactyl #1045 By IV. 243 Ida and Dactyl NIMS Spectra Band I/Band Area Ratio Plot S Asteroid Classification 1.15 1.15 James Granahan idu019radiance Reflectance Spectrum Figure 2 plots the reflectance 3 Science Application International Corporation Olivine Field 2.5 1.1 1.1 spectra derived from the SI 10932 Blake Lane 2 Olivine-Orthopyroxene Mixing Line Bealeton, VA 22712 1.5 radiance spectral data products 1.05 1.05 1 m) m) SII µ 243 Ida µ e-mail: [email protected] Reflectance Scaled 0.5 along with corresponding Dactyl 243 Ida 0 SIII Dactyl 0 1 2 3 4 5 6 Band I CenterBand ( 1 Ordinary Chondrite Field I CenterBand ( 1 Wavelength (µm) Galileo mission Solid State I. Abstract idu020radiance Reflectance Spectrum Imager (SSI) imagery of 243 Ida SIII SV 4.5 0.95 Basaltic Achondrite Field 0.95 4 3 SIV 3.5 and Dactyl. The reflectance SVI 3 2.5 SVII 0.9 0.9 Infrared spectra of asteroid 243 Ida and its satellite Dactyl have 2 spectra were created by ratioing 0 0.5 1 1.5 2 2.5 3 0 0.5 1 1.5 2 2.5 3 1.5 Band Area Ratio (Band II/ Band I) Band Area Ratio (Band II/ Band I) Scaled Reflectance Scaled 1 features that are similar to those of L6 and LL4 chondrite meteorites. 0.5 the radiance spectra by solar 0 0 1 2 3 4 5 6 Figure 4. Meteorite, 243 Ida, Figure 5. 243 Ida, Dactyl, and The 243 Ida and Dactyl data are from Galileo spacecraft Near Wavelegnth (µm) spectra from the Infrared 4 and Dactyl mineral values S asteroid subtypes Infrared Mapping Spectrometer (NIMS) observations obtained on idu035radiance Reflectance Spectrum Handbook and normalized at 1 2.5 August 28, 1993. This NIMS data has been radiometrically calibrated 2 1.5672 micrometers. Figure 3 VI. A Comparison with Ordinary Chondrites during an effort to create spectral data products for the NASA 1.5 1 is a plot of the radiance spectra Planetary Data System (PDS) and now can be compared to existing Reflectance Scaled 0.5 that were used in the creation Figure 6 compares 243 Ida and Dactyl spectral features with ordinary 0 0 1 2 3 4 5 6 2 meteorite measurements. A comparison of one- and two-micrometer Wavelength (µm) of the reflectance spectra chondrite values collected by Dunn et al. The bulk of 243 Ida band centers and band areas of these recently calibrated 243 Ida idu028radiance Reflectance Spectrum illustrated in Figure 2. spectra map to values that are consistent with those of L chondrites, 2.5 and Dactyl data correspond to measurements of ordinary chondrite 2 243 Ida and Dactyl Radiance Spectra specifically within the L6 chondrite values. Dactyl and 243 Ida 600 meteorite spectra.2 This abstract describes the effort to create 243 Ida 1.5 spectra from the vicinity of Vienna Regio have values that correspond 1 500 and Dactyl radiance spectral archive products and their comparison Reflectance Scaled 0.5 IDU005 to those of LL chondrites. The Dactyl measurements are closest to IDU006 0 400 IDU007 0 1 2 3 4 5 6 IDU019 with known meteorite measurements. Wavelength (µm) those of LL4 chondrites. These finding suggest that Dactyl may be IDU020 300 IDU022 idu022radiance Reflectance Spectrum IDU028 a fragment of 243 Ida derived from impact disruption of materials IDU032 II. Introduction 2.5 200 IDU033 Radiance (µWatt/cm2*Sr*µm) Radiance 2 IDU035 near Afron crater. L and LL chondrites have different degrees of Dactyl002 1.5 6 100 ida_nims_002 oxidation. This suggests that 243 Ida was assembled from ordinary ida_nims_004 Asteroid 243 Ida and satellite Dactyl (Figure 1) 3 1 Scaled Reflectance Scaled 0.5 0 0 1 2 3 4 5 6 chondrite materials that were derived from two different portions of 0 Wavelength (µm) • S-class asteroid 0 1 2 3 4 5 6 the solar nebula. Wavelength (µm) Figure 3. 243 Ida and Dactyl • Koronis family member idu032radiance Reflectance Spectrum radiance spectra Ordinary Chondrite, 243 Ida, and Dactyl Plot 3.5 1.08 • 53.6 x 24.0 x 15.2 km 3 2.5 V. S-Type Asteroid Minerals • Semi-major Axis 2.86 AU 2 1.06 1.5 1 and Subtype Scaled Reflectance Scaled • Orbital period 4.84 years 0.5 1.04 LL4 Chondrite 0 • Encountered by Galileo on August 28, 1993 0 1 2 3 4 5 6 LL5 Chondrite Wavelength (µm) S-type asteroids can be 1.02 LL6 Chondrite idu033radiance Reflectance Spectrum L4 Chondrite 4 classified on the basis of 1 L5 Chondrite 3.5 3 L6 chondrite 2.5 observed spectral signatures Band I Center (µm) I Center Band 0.98 H4 Chondrite 2 1.5 IDU033 of silicate minerals. Gaffey H5 chondrite 1 Scaled Reflectance Scaled 0.5 5 0.96 H6 Chondrite 0 et al. used the measurement 0 1 2 3 4 5 6 243 Ida Wavelength (µm) of spectral absorption features 0.94 Dactyl idu006radiance Reflectance Spectrum 4 in the vicinity of 1 (Band I) 0.92 3.5 0 0.2 0.4 0.6 0.8 1 1.2 3 2.5 and 2 micrometers (Band Band Area Ration (Band II/Band I) 2 1.5 II) to identify minerals and 1 Figure 1. A false-color Image of 243 Ida and Dactyl (using 0.4, Reflectance Scaled 0.5 Figure 6. Ordinary chondrite values and 243 Ida and Dactyl 0 classes of S-type asteroids. 0.56, and 0.75 μm images at 105 m/pixel) 0 1 2 3 4 5 6 Wavelength (µm) measurements III. Data List Figure 4 illustrates that these idu005radiance Reflectance Spectrum VII. Conclusions and References 5 spectral measurements from 4.5 4 3.5 the previously described NIMS The current archive effort has created radiance spectra of asteroid 3 2.5 The NIMS spectral Galileo spacecraft observations of asteroid 2 1.5 data indicate that both 243 243 Ida and satellite Dactyl from archived uncalibrated data number Reflectance Scaled 1 0.5 243 Ida asteroid system indicate that it is composed of L and LL 0 Ida and Dactyl have silicate NIMS image files stored in the NASA PDS Imaging Node. The 0 1 2 3 4 5 6 Wavelength (µm) chondrite materials. Most of 243 Ida has values that are consistent calibrated data have been submitted to the NASA PDS Small Bodies mineral (pyroxene and olivine) idu007radiance Reflectance Spectrum with L6 chondrites. Measurements of 243 Ida in the Vienna Regio 3.5 abundances that correspond Node for archiving. The data number values were converted using 3 are similar to those of LL5 and LL6 chondrites. Dactyl is similar to 2.5 to those of ordinary chondrite calibration factors calculated for the Galileo NIMS observations 2 1.5 measurements of LL4 chondrites. These materials differ from each 1 meteorites. S asteroid subtypes of Europa and Callisto. Both point spectrum and spectral image Reflectance Scaled 0.5 other in the relative abundance of NiFe-to-silicate ratios and degrees 0 also are designated by the products were created. Point spectrum files are labeled with a prefix 0 1 2 3 4 5 6 Wavelength (µm) of oxidation. All are classified as the SIV subtype of S asteroids. The of “idu” or “dactyl.” Spectral image files have the prefix of “ida_ relative abundance of silicate ida_nims_004_radiance Reflectance similarity of the 243 Ida and Dactyl LL chondrite-like measurements nims.” The number in the file name matches the file numbering Spectrum Sample minerals. SI are asteroids with 4 suggests that the asteroid moon may be an impact fragment of 243 3.5 3 a dominant olivine signatures. found in the NASA PDS imaging node. Processing of the spectral 2.5 2 Ida. The existence of both L and LL chondrite-like signatures in 1.5 SII are objects where a high image products included spatial registration of NIMS pixels to 1 Scaled Reflectance Scaled 0.5 this asteroid system also suggests that these objects are derived from 0 olivine abundance exists with narrow-angle camera Galileo imagery of 243 Ida. The following are 0 1 2 3 4 5 6 Wavelength (µm) ordinary chondrite materials from two different sources. some calcic pyroxene. SIII the processed radiance data files: dactyl002radiance Reflectance Spectrum and SV are calcic pyroxene- File Name Channels Target Observation Target Pixel 2.5 This data archive and initial analysis work was made possible by support Start (UT) Distance (km) Size (km) 2 bearing asteroids. SIV are 1.5 from NASA’s Planetary Mission Data Analysis Program. The radiance idu019radiance 17 243 Ida 14:57:59 83244.2 48.819 1 asteroids with olivine and idu020radiance 17 243 Ida 15:21:13 66040.8 33.007 Reflectance Scaled data used for this poster has been submitted as Flexible Image Transport 0.5 pyroxene abundances similar idu035radiance 17 243 Ida 15:25:25 64069.1 32.021 0 7 0 1 2 3 4 5 6 System and text file formats for archival in the NASA PDS. idu028radiance 17 243 Ida 15:37:07 55639.0 27.806 Wavelength (µm) to those of ordinary chondrites. idu022radiance 17 243 Ida 15:44:29 33021.8 16.498 1Carlson, R. W., et al. (1994), Bulletin of the American Astronomical Society, 26, idu032radiance 17 243 Ida 15:48:39 47087.6 23.530 ida_nims_002_radiance Reflectance SVI are objects where Spectrum Sample 1156. idu033radiance 17 243 Ida 16:11:57 29819.8 14.896 4 orthopyroxene has a higher 2 3.5 Dunn, T.
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