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Planetary Science Institute PLANETARY SCIENCE INSTITUTE N7'6-3qo84 (NAS A'-CR:1'V7! 3 ) ASTEROIDAL AND PLANETARY ANALYSIS Final Report (Planetary Science Ariz.) 163 p HC $6.75 Inst., Tucson, CSCL 03A Unclas G3/89 15176 i-'' NSA tiFACIWj INP BRANC NASW 2718 ASTEROIDAL AND PLANETARY ANALYSIS Final Report 11 August 1975 Submitted by: Planetary Science Institute 252 W. Ina Road, Suite D Tucson, Arizona 85704 William K. Hartmann Manager TASK 1: ASTEROID SPECTROPHOTOMETRY AND INTERPRETATION (Principal Investigator: Clark R. Chapman) A.* INTRODUCTION The asteroid research program during 1974/5 has three major goals: (1) continued spectrophotometric reconnaissance of the asteroid belt to define compositional types; (2) detailed spectrophotometric observations of particular asteroids, especially to determine variations with rotational phase, if any; and (3) synthesis of these data with other physical studies of asteroids and interpretation of the implications of physical studies of the asteroids for meteoritics and solar system history. The program has been an especially fruitful one, yielding fundamental new insights to the nature of the asteroids and the implications for the early development of the terrestrial planets. In particular, it is believed that the level of understanding of the asteroids has been reached, and sufficiently fundamental questions raised about their nature, that serious consideration should be given to possible future spacecraft missions directed to study a sample of asteroids at close range. Anders (1971) has argued that serious consideration of asteroid missions should be postponed until ground-based techniques for studying asteroids had been sufficiently exploited so that we could intelligently select appropriate asteroids for spacecraft targeting. It is clear that that point has been reached, ,and now that relatively inexpensive fly-by missions have been discovered to be possible by utilizing Venus and Earth gravity assists (Bender and Friedlander, 1975), serious planning for such missions ought to begin. This final report will not repeat the numerous results already presented in the first three Quarterly Reports. Reference is made to those reports and to papers that have been published or are in press that are based on this work. We begin with a brief description of the work conducted in the fourth quarter, and conclude with a summary of the entire year's effort. B. FOURTH QUARTERLY REPORT During the fourth quarter, progress was made in several areas includ­ ing further data reduction and preparation of manuscripts for publication. In addition, preparations were conducted for a major spectrophotometric observing program at the Mauna Kea Observatory that will be underway during the final days of the quarter. Reduction of February Data Although the spectrophotometric asteroid measurements made in February were reduced in a preliminary fashion during the previous quatter, final reduction was completed during the present quarter. The qualitative results are unchanged, however. Numerous C-type (carbonaceous) objects were observed, plus a few of very distinctive composition. It is intended that a manuscript will -1- ' TASK I: ASTEROID SPECTROPHOTOMETRY AND INTERPRETATION­ (Principal Investigator: Clark R. Chapman) A.* INTRODUCTION The asteroid research program during 1974/5 has three major goals: (1) continued spectrophotometric reconnaissance of the asteroid belt to define compositional types; (2) detailed spectrophotometric observations of particular asteroids, especially to determine variations with rotational phase, if any; and (3) synthesis of these data with other physical studies of asteroids and interpretation of the implications of physical studies of the asteroids for meteoritics and solar system history. The program has been an especially fruitful one, yielding fundamental new insights to the nature of the asteroids and the implications for the early development of the terrestrial planets. In particular, it is believed that the level of understanding of the asteroids has been reached, and sufficiently fundamental questions raised about their nature, that serious consideration should be given to possible future spacecraft missions directed to study a sample of asteroids at close range. Anders (1971) has argued that serious consideration of asteroid missions should be postponed until ground-based techniques for studying asteroids had been sufficiently exploited so that we could intelligently select appropriate asteroids for spacecraft targeting. It is clear that that point has been reached, and now that relatively inexpensive fly-by missions have been discovered to be possible by utilizing Venus and Earth gravity assists (Bender and Friedlander, 1975), serious planning for such missions ought to begin. This final report will not repeat the numerous results already presented in the first three Quarterly Reports. Reference is made to those reports and to papers that have been published or are in press that are based on this work. We begin with a brief description of the work conducted in thefourth quarter, and conclude with a summary of the entire year's effort. B. FOURTH QUARTERLY REPORT During the fourth quarter, progress was made in several areas includ­ ing further data reduction and preparation of manuscripts for publication. In addition, preparations were conducted for a major spectrophotometric observing program at the Mauna Kea Observatory that will be underway during the final days of the quarter. Reduction of February Data Although the spectrophotometric asteroid measurements made in February were reduced in a preliminary fashion during the previous quarter, final reduction was completed during the present quarter. The qualitative results are unchanged, however. Numerous C-type (carbonaceous) objects were observed, plus a few of very distinctive composition. It is intended that a manuscript will -I­ be prepared by McCord and Chapman (to be the third part of the series published earlier this year in the Astrophysical Journal (McCord and Chapman, 1975a,b), based on the data obtained last summer, in February 1975, May 1975, and the present observing run in Hawaii. 43a Eros Campaign Chapman concluded final reduction of lros spectrophotometry obtained on 13 February at Kitt Peak National Observatory (replacing the preliminary reduction reported in the previous Quarterly fteport). Chapman worked jointly with C. Pieters, M. Gaffey, and T. McCord (MIT) in developing an interpreta­ tion of these data combined with similar data obtained by Pieters at Cerro Tololo. A paper has beenwritten and submitted to Icarus -(see Appendix A). The fundamental conclusion is that-Eros'seems to-becomposed of an assemblage of moderately high temperature minerals (including ioli, olivifie, and pyroxene) such as the H or L-tipe ordinary chodrite . H6wever, detailed -interpretation of the spectrum reveals .that the particle size of -the iron on Eros' surface must be much finer than that produced by hand-crushing of a meteorite sample in the labotatory. -In the absence of appropriate laboratory work it would be premature to assert categorically that Eros is.hn ordinary ch6ndiite, but'it does seem probable. No major compositional variations with rotation were detected.on Eros. March Radiometry - Chapman assisted D. Morrison- (U. of Hawaii) on an observing-run during mid-March .during which 10 mic-ron measurements were obtained of 22 asteroids. During the present quarter, Morrisonand Chapman prepared a manu­ script (submitted to the-Astrophysical Journal, see Appendix B) summarizing the results. The first small main-belt asteroids to be measured radiometrically were sampled during this -un. Chapman will present a joint paper on these data at the San Diego meeting of the American Astronamical. Society. March .JHKL Spectropiotometry DuriAgthe final night of the Morrison/Chapman observing run in March, near infrared photometric measurements were made of eleven asteroids (plus two satellites of Saturn) in the J, H, K, and (for 2 asteroidS) L standard' filters. Although this portion of the reflection spectrum (1 to 3 microns) contains a number of diagnostic absorption bands, detailed'spectra have been measured .so far for only 2 asteroids' (4 Vesta, Larson and Fink, 1975,7and 433 Eros, Larson et al, 1975). While broadland-data-are less diagnostic of composit-iqn, they do have some interpretive value as shown by Johnson et al (19.75). Preliminary reduction has been completed of our own photonetry, although the calibration is subject to change. As shown in Fig. 1-1, color ratios indicate a moderate spread in asteroid colors over the K/J vs K/H plane; implying compositional differences that do not show a straightforward'cortelatipti with the C and S compositional types describe-d by Chapman et al (1975). Both -2­ 0,7 aOA RW - RAw-K/7" 129 Antigone and 6 Hebe, at opposite ends of this plot, seem otherwise to be typical S objects. Detailed intrepretation at this time is premature, but study of the spectral behavior of asteroids in this mid-infrared region is important because of the bearing it has on the metallicity of the S-type asteroids. Chapman and Morrison will be preparing a paper on this topic. May Spectrophotometry The spedtrophotometry reported in the previous Quarterly Report has now been reduced for most asteroids observed. Some representative spectral reflectance curves are illustrated in Fig. 1-2. The most significant discovery is that a second large asteroid in the main belt (471 Papagena) seems to have the composition of a metamorphosed ordinary
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