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1.
VJHK measurements of J6 Himalia and S9 Phoebe, using the new NASA IRTF telescope, show that these objects have carbonaceous chondritic type colors in the 0.5- to 2.2-μm region. For Phoebe, this is in contrast to the JHK colors published by Cruikshank (1980), which indicated that the satellite's surface was unlike the material found on asteroids and on the dark side of Iapetus. J6 is known to have a low albedo from thermal infrared studies (Cruikshank, 1977), and the new VJHK observations of S9 imply that it also has a low albedo. The H and K reflectances of S9 are slightly lower than those of J6, suggesting some slight difference in surface composition or a contamination by foreign material. The conjectured low albedo of S9 can be tested with measurements in the thermal infrared. 相似文献
2.
Robert Hamilton Brown 《Icarus》1983,56(3):414-425
New reflectance spectra at 3.5% resolution have been obtained for Ariel, Titania, Oberon, and Hyperion in the 0.8- to 1.6-μm spectral region. The new spectra show no absoptions other than the 1.5-μm water-ice feature (within the precision of the data), and demonstrate extension into the 0.8- to 1.6-μm region of the 1.5- to 2.5-μm spectral similarity of Ariel to Hyperion (R. H. Brown and D. P. Cruikshank (1983). Icarus55,93-92). The new data confirm the presence of dark, spectrally bland component on/in the water-ice surfaces of the Uranian satellites, which, with some reservations, has spectral similarities to the dark substance on the leading side of Iapetus and the dark material on/in the surface of Hyperion, as well as other dark, spectrally neutral substances such as charcoal. Attempts were made to match the spectra of Ariel, Titania, and Oberon with additive reflectance mixes (areal coverage) of fine-grained water frost and various dark components such as charcoal, lampblack, and charcoal-water-ice mixtures. The results were broad limits on the amounts of possible areal coverage of a charcoal-like spectral component on the surfaces of the Uranian satellites, but the data are not of sufficient precision to conclusively determine whether the dominant mode of contaminant dispersal is areal or voluminal. The effect of highly variegated albedos on the diameters derived by R. H. Brown, D. P. Cruikshank, and D. Morrison (1982a) (Nature300, 423–425) is found to be small. 相似文献
3.
Bonnie J. Buratti 《Icarus》1985,61(2):208-217
A radiative transfer model, derived largely from the work of B.W. Hapke (1981, J. Geophys. Res.86, 3039–3054) and J.D. Goguen (1981, Ph.D. thesis, Cornell University, Ithaca, N.Y.), is fit to Voyager imaging observations of Europa, Mimas, Enceladus, and Rhea. It is possible to place constraints on the single-scattering albedo, the porosity of the optically active upper regolith, the single-particle phase functions, and, in the cases of Europa and Mimas, the mean slope angle of macroscopic surface features. The texture of the surfaces of the Saturnian satellites appears to be similar to the Earth's moon. However, Europa is found to have a distinctly more compact regolith and a more forward-scattering single-particle phase function. 相似文献
4.
John Caldwell 《Icarus》1975,25(3):384-396
Broadband filter photometry from 2100 to 4300 Å has been obtained by OAO-2 for the following objects: The Galilean satellites; Titan; the rings of Saturn; and three asteroids. Agreement with independent ground-based photometry in the region of overlap is good. The previously known decrease in reflectivity from visual to ground-based ultraviolet wavelengths continues to 2590 Å for all these objects. Europa's reflectivity continues to decline towards 2110 Å, and the rings' reflectivity levels off from 2590 to 2110 Å. Other targets were too faint at 2110 Å to be measured reliably by OAO-2.The low ultraviolet albedo of Titan has important implications for that planet's atmospheric structure (Caldwell, Larach, and Danielson, 1973; Danielson, Caldwell, and Larach, 1973; Caldwell, 1974b). The ultraviolet reflectivity of Saturn's rings is suggestive of a two-component system, one being pure H2O particles. The ultraviolet albedos of the Galilean satellites are consistent with existing upper limits for atmospheric abundances, but require either that former estimates of the fractional coverage of H2O frost are too high, an unlikely circumstance, or that the frost has been darkened by some external agent in the space environment. 相似文献
5.
The Tunguska event on 30 June 1908 has been subjected to much speculation within different fields of research. Publication of the results of the 1961 expedition to the Tunguska area (Florensky, 1963) supports that a cometary impact caused the event. Based on this interpretation, calculations of the impactor energy release and explosion height have been reported by Ben-Menahem (1975), and velocity, mass, and density of the impactor by Petrov and Stulov (1975). Park (1978) and Turco et al., 1981, Turco et al., 1982, used these numbers to calculate a production of ca. 30 × 106 tons of NO during atmospheric transit. This paper presents a high-resolution study of nitrate concentration in the Greenland ice sheet in ca. 10 years covering the Tunguska event. No signs of excess nitrate are found in three ice cores from two different sites in Greenland in the years following the Tunguska event. By comparing these results with results for other aerosols generally found in the ice, the lack of excess NO3? following the Tunguska event can be interpreted as indicating that the impactor nitrate production calculated by Park (1978) and Turco et al., 1981, Turco et al., 1982 are 1–2 orders of magnitude too high. To explain this it is suggested, from other lines of reasoning, that the impactor density determined by Petrov and Stulov (1975) probably is too low. 相似文献
6.
Olav L. Hansen 《Icarus》1977,31(4):456-482
A new radiometric model for disk-integrated photometry of asteroids is presented. With empirical support from photometry of Mercury and the Moon, the model assumes that observed sunward beaming of the infrared emission is due to craters. In contrast to earlier theoretical studies of the lunar emission, the observable flux ratio between a cratered sphere and a smooth sphere is calculated for large ranges in wavelength, temperature, and phase angle. Revised diameters and albedos based on the crater model are given for 84 asteroids. The revised values are in good agreement with Morrison's (1977) radiometric results. It is shown that the systematic discrepancy between radiometric and polarimetric albedos (Zellner and Gradie, 1976) is probably a double-valued function of albedo. Some typical geometric albedos from this paper, Morrison (1977), and Zellner and Gradie (1976), respectively, are: Ceres (0.050 ± 0.005, 0.053 ± 0.004, 0.068), Vesta (0.235 ± 0.032, 0235 ± 0.11, 0.271), mean C type (0.031 ± 0.009, 0.035 ± 0.009, 0.061 ± 0.005), mean S type (0.117 ± 0.030, 0.136 ± 0.032, 0.181 ± 0.23), and mean M type (0.105 ± 0.037, 0.115 ± 0.033, 0.157 ± 0.079). Areas of disagreement between radiometry and polarimetry are underscored, and research to resolve them is suggested. 相似文献
7.
New spectrophotometry from 1.5 to 2.5 μm is reported for the Uranian satellites Titania, Oberon, and Umbriel. A spectrum of the rings of Uranus from 2.0 to 2.4 μm is also reported. No evidence is found for frost covering the surface of the ring material, consistent with the low albedo of the rings (PK = 0.03) previously reported by Nicholson and Jones (1980). The surfaces of the satellites are found to be covered by dirty water frost. Assuming albedos of the frost and gray components covering the Uranian satellites to be the same as the light and dark faces of Iapetus, radii are derived that are roughly twice those inferred from the assumption of a visual albedo of 0.5. 相似文献
8.
Absolute spectrophotometry of Neptune from 3390 to 7800 Å, with spectral resolution of 10 Å in the interval 3390–6055 and 20 Å in the interval 6055–7800 Å, is reported. The results are compared with filter photometry (Appleby, 1973; Wamsteker, 1973; Savage et al., 1980) and with synthetic spectra computed on the basis of a parameterization proposed by Podolak and Danielson (1977) for aerosol scattering and absorption. A CH4/H2 ratio of is derived for the convectively mixed part of Neptune's atmosphere, and constrains optical properties of hypothetical aerosol layers. 相似文献
9.
L.H. Wasserman 《Icarus》1974,22(1):105-110
The nightime cooling of the Jovian atmosphere near the occulation level of 1014cm?3 is calculated using the models of Strobel (1973) and Strobel and Smith (1973). The amount of cooling is found to depend on χ, the methane mixing ratio; μ the mean molecular weight; and the sunrise temperature. Using the range of sunrise (emersion) temperatures observed by Veverka et al. (1974), the overnight cooling is calculated to be 1.5–5.5°K, if reasonable assumptions are made for χ and μ. The argument may be reversed to show that the agreement in measured sunrise and sunset temperatures obtained by other observers of the β Sco occulation implies that χ cannot be significantly greater than the generally accepted value of 7 ×10?4. 相似文献
10.
The 5ν1 absorption band of NH3 is displayed from 6418 to 6550 Å. The total band intensity has been measured: SB = 0.66 cm?1m?1amagat?1. Line intensities and self-broadening coefficients have been measured for some of the prominent lines. Our line intensities are in good agreement with those of Rank et al. (1966), but are about 2 times greater than those of Mason (1970). The spectrum displayed was obtained photoelectrically at a pressure of 0.061 atm, and shows many more lines than the spectrum obtained by McBride and Nicholls (1972a) at a pressure of 0.39 atm. Therefore, our new measurements can provide the basis for making a more complete rotational analysis than those of McBride and Nicholls (1972a).Since the total band absorption has previously been measured by others on moderate resolution photoelectric scans of the spectra of Jupiter and Saturn, we can use the band intensity to derive the NH3 abundance in the atmospheres of these two planets. The NH3 abundances in a single vertical path obtained by this method are about 10m amagat for Jupiter and 2m amagat for Saturn. These results are in agreement with previous results obtained from higher resolution photographic spectra. 相似文献
11.
Ronald C. Taylor 《Icarus》1985,61(3):490-496
Refinements to the pole-determination method photometric astrometry (PA) were completed in 1983 (R. C. Taylor and E. F. Tedesco, 1983, Icarus54, 13–22). A goal is to redo the pole analysis for every asteroid whose pole had been determined from earlier versions of PA: Previous PA poles are reviewed in this paper. Asteroid 433 Eros is in that collection and has redone. The result are prograde rotation; a sidereal period of 0.219588 ± 0.000005 day; and a north pole at 22° longitude, +9° latitude. The uncertainty of the pole is 10°. The pole position of Eros determined by C.D. Vesely (1971, In Physical Studies of Minor Planets (T. Gehrels, Ed.), pp. 133–140, NASA SP-267) and Dunlap (1976, Icarus28, 69–78), using earlier versions of photometric astrometry, were within 21 and 7°, respectively, of the present result. 相似文献
12.
Absolute spectrophotometry of four regions on the visible disk of Saturn (north and south polar regions, equatorial band, south “temperate” region) from 3390 to 8080 Å is reported. Spectral resolution is 10 Å in the interval 3390–6055 Å, and 20 Å; aperture size is 1.92 arcsec. The explicit purpose of our observations was to provide ground-based photometric calibration for the Pioneer Saturn Imaging Photopolarimeter (IPP). We also compare our data with earlier spectrophotometric measurements of Saturn (R.L. Younkin and G. Munch, 1963,Mem. Soc. Roy. Sci. Liege7, 123–136; W.M. Irvine and A.P. Lane, 1971,Icarus16, 10–26; T.B. McCord, T.V. Johnson, and J.H. Elias, 1971,Astrophys. J.165, 413–424) and with the M. Podolak and R.EE. Danielson (1977)Icarus30, 479–492) parameterization of “Axel Dust.” The latter reproduces the broad features but not the details of the observed spectral reflectivity (I/F). We find that large depths of clear molecular hydrogen (>14 km-am in the temperate regions) are needed to match the observed upturn in reflectivity shortward of 3800 Å. 相似文献
13.
Dale W. Smith 《Icarus》1975,25(3):447-451
Brinkmann (1973) has suggested that the Galilean satellites might briefly manifest a brightening at mid-eclipse due to a concentration of light refracted into the geometric umbra of Jupiter by the atmosphere around the terminator. Results obtained using two different models of the Jovian atmosphere indicate that such a brightening is unlikely even for Callisto due to the probable aerosol concentration in the Jovian atmosphere at the relevant altitudes. 相似文献
14.
A contradiction in the sulfuric acid cloud hypothesis of Venus, i.e., nondetection of 4.8 μm polarization by Landau (1975), is examined on the basis of the multiple scattering calculations for the cloud model of Hansen and Hovenier (1974) including an internal heat source. Results show that the polarized thermal component cannot depolarize the scattered sunlight, and therefore a large polarization of about 13% is expected at a phase angle of 110° and wavelength of 4.8 μm, in contrast with Landau's measurements. Our computations are, however, in agreement with the measurements by S. Sato et al. (in “Proceedings, 10th Lunar and Planetary Symposium,” pp. 179–182. Institute of Space and Aeronautical Science, University of Tokyo, July 11–13, 1977). 相似文献
15.
Dale P. Cruikshank 《Icarus》1980,41(2):240-245
The reflectance spectrum of Io is presented from 2.8 to 5.2 μm, extending the earlier results of D. P. Cruikshank, T. J. Jones, and C. B. Pilcher (1978, Astrophys. J. 225, L89–L92), and demonstrating the full extent of the broad and deep spectral absorption between 3.5 and 4.8 μm. Laboratory spectra of nitrates and carborates diluted with sulfur do not satisfactorily reproduce the Io spectrum, but new information based on the recently discovered volcanic activity on the satellite lead to consideration of other classes of compounds as reported in a companion paper (F. P. Fanale, R. H. Brown, D. P. Cruikshank, and R. N. Clark, 1979, Nature280, 761–763). 相似文献
16.
Observations of Saturn's satellites and external rings during the 1980 edge-on presentation were obtained with a focal coronograph. A faint satellite traveling in the orbit of Dione and leading it by 72° has been detected, together with the two inner satellites already suspected (cf. J. W. Fountain and S. M. Larson, 1978,Icarus36, 92–106). The external ring has been observed on both east and west sides; it may extend up to Saturn radii, and appears structured. 相似文献
17.
A convenient photometric function for many particulate surfaces is the generalization of the Lommel-Seeliger law derived by Hapke (1963) and Irvine (1966). This generalization accounts for the effects of mutual shadowing among particles, but still assumes that multiple scattering within the surface layer can be neglected—an assumption which is evidently valid for dark surfaces. We describe a series of laboratory measurements which test the range of validity of this basic assumption, and the applicability of the Hapke-Irvine photometric function, for particulate surfaces whose normal reflectances ranges from 0.04 to 1.04. We find that multiple-scattering effects can be neglected, and that the Hapke-Irvine function can be used, for particulate surfaces whose normal reflectance is about 0.3, or less. The function is definitely inapplicable to surfaces whose normal reflectance exceeds 0.4. 相似文献
18.
We report new visual and 20-μm photometry obtained when Hektor was seen nearly along its rotation axis. The visual amplitude was near its minimum, only 0.06 mag, confirming the Dunlap-Gehrels (1969) rotation model. The new observations confirm and refine the large size and low albedo assigned by Cruikshank (1977) from observations of the opposite rotation pole. The albedo of this pole is found to be pv = 0.022 ± 0.003, overlapping the uncertainty of Cruikshank's 0.03 value for the opposite pole. The low albedo makes Hektor roughly three times bigger than estimates of a few years ago. The light variations are interpreted as due to elongated shape. If this is correct, Hektor is both the largest and most elongated known Trojan, as well as being the most elongated known asteroid of its size. From considerations of Trojans' peculiar properties, we propose that Hektor is a somewhat dumbbell shaped object roughly 150 × 300 km in size, resulting from partial coalescence of two primitive spheroidal planetesimals during a relatively low-speed collision in the Trojan Lagrangian cloud, with energy too low for complete disruption. Calculations supporting this model indicate that Trojans may be less altered by collisions than belt asteroids. Observations in 1979 and 1980 can help test this model. A note added on July 17, 1978 relates our result to recent evidence of possible binary asteroid pairs, which may also arise from early low-velocity asteroid-asteroid interactions. 相似文献
19.
Kevin H. Baines 《Icarus》1983,56(3):543-559
High-resolution (0.1-Å) spectra of the 6818.9-Å methane feature obtained for Jupiter, Saturn, and Uranus by K. H. Baines, W. V. Schempp, and W. H. Smith ((1983). Icarus56, 534–542) are modeled using a doubling and adding code after J. H. Hansen ((1969). Astrophys. J.155, 565–573). The feature's rotational quantum number is estimated using the relatively homogeneous atmosphere of Saturn, with only J = 0 and J = 1 fitting the observational constraints. The aerosol content within Saturn's northern temperate region is shown to be substantially less than at the equator, indicating a haze only half as optically thick. Models of Jupiter's atmosphere are consistent with the rotational quantum-number assignment. Synthetic line profiles of the 6818.9-Å feature observed on Uranus reveal that a substantial haze exists at or above the methane condensation region with an optical depth eight times greater than previously reported. Seasonal effects are indicated. The methane column abundance is 5 ± 1 km-am. The mixing ratio of methane to hydrogen within the deep unsaturated region of the planet is 0.045 ± 0.025, based on an H2 column abundance of 240 ± 60 km-am (W. H. Smith, W. Macy, and C. B. Pilcher (1980). Icarus43, 153–160), thus indicating that the methane comprises between one-sixth and one-half of the planet's mass. However, proper reevaluation of H2 quadrupole features accounting for the haze reported here may significantly reduce the relative methane abundance. 相似文献
20.
The minor planet 164 Eva passed through opposition on December 1, 1975 with a magnitude Bopp = 11.3 mag. Photoelectric observations at the Observatory of Torino, Italy, were carried out in two nights on Oct. 27/28 and Nov. 11, each with a run of about 3 hr. Two further successful photoelectric observations were carried out at the OHP, France, each with a run of about 6 hr. From all observed parts of the lightcurve a resulting synodic period of rotation of about 27.3 hr can be deduced, with a range of the total amplitude of at least Δm = 0.07 mag. With this period of 27.3 hr the minor planet 164 Eva is one more long period object, falling now between 654 Zelinda (H. J. Schober, 1975, Astron. Astrophys.44, 85–89) and 139 Juewa (J. Goguen et al., 1976, Icarus29, 137–142), at the high end in the histogram of the distribution of minor planet rotation periods. 相似文献