James. R. Johnson

The 1.7- to 4.2-μm spectrum of asteroid 1 Ceres: Evidence for structural water in clay minerals

Abstract A high-resolution Fourier spectrum (1.7–3.5 μm) and medium-resolution spectrophotometry (2.7–4.2 μm) were obtained for Asteroid 1 Ceres. The presence of the 3-μm absorption feature due to water of hydration was confirmed. The 3-μm feature is compared with the 3-μm bands due to water of hydration in clays and salts. It is concluded that the spectrum of Ceres shows a strong absorption at 2.7–2.8 μm due to structural OH groups in clay minerals. The dominant minerals on the surface of Ceres are therefore hydrated clay minerals structurally similar to terrestrial montmorillonites. There is also a narrow absorption feature at 3.1 μm which is attributable to a very small amount of water ice on Ceres. This is the first evidence for ice on the surface of an asteroid.

Detection of a CH4 atmosphere on Pluto

A ratio spectrum of Pluto shows methane absorption bands at 6200, 7200, 7900, 8400, 8600, 8900, and 10,000 A. The heavy saturation of the 8900 band as compared to the other bands indicates a gaseous origin for the observed absorptions. A total methane abundance of 80 + or - 20 m-am is derived, and an upper limit to the total pressure of approximately .05 atm is set. The methane atmosphere would be stable if the mass of Pluto is increased 50% over its present value and its radius is 1400 km. A heavier gas mixed with the methane atmosphere would also aid its stability.

Charge coupled device (CCD) spectroscopy of comets: Tuttle, Stephan-Oterma, Brooks 2, and Bowell

Abstract Spectra of the four comets, Tuttle, Stephan-Oterma, Brooks 2, and Bowell, were taken with a prototype space telescope charge coupled device (CCD) camera using a 500 × 500 Texas Instruments chip. The spectra extended from 5600 to 10,400 A at a resolution of ∼25 A . The spatial coverage along the slit was 180⇑; its resolution was defined by the seeing ( 2–3 ⇑ ). Both absolute flux scales and spectral albedos were determined with the data reduction procedure which included flat fielding and sky subtraction. Comet Tuttle displayed extensive emissions by NH2, the red system of CN, and the C2 Swan bands as well as emissions by the forbidden oxygen lines [OI] 1D at 6300 and 6364 A, and the ionic species H2O+. A feature at 6851 A has been tentatively identified as the 3-0 band of CS+. Notable is the absence of the C2 Phillips bands whose transitions are optimally placed in our spectrum. The much dustier comet, Stephan-Oterma showed emissions by CN, NH2, and [OI] while only [OI] could be discerned in the noisier Brooks 2 spectrum. The fresh comet Bowell exhibited an unusually extended coma with an albedo times cross section two orders of magnitude larger than the other comets, a very flat albedo spectrum, and no emission features. For Tuttle and Stephan-Oterma, CN and NH2 column densities using a number of bands were calculated. The CN band intensity ratios show good agreement with theoretical fluorescence models. The spatial profiles for CN and NH2 were compared to two step Haser model decay calculations. The scale lengths most consistent with the data were compared with values previously reported and with values expected for various photodissociation reactions. Production rates were calculated for CN and NH2. These should be less model dependent because of the simultaneous collection of spectral and spatial information. The production rate ratios of the parents of CN and NH2 to the parent of OH are several orders of magnitude smaller than the solar abundance ratios of C/O and N/O.

Spectrophotometry and upper limit of gaseous CH4 for Triton

Abstract Spectra of Triton with a CCD spectrometer yielded a relative spectral reflectivity curve from 0.56 to 1.05 μm at a resolution of 25 A. Using low-temperature band model parameters from Fink et al. (1980), an upper limit for the one-way path gaseous CH4 abundance of 1 m-am was derived.