Search

The likely existence of bodies orbiting the Sun with aphelia Q < 0.983 AU has been suggested by numerical simulations of the dynamical evolution of the near-Earth objects (NEOs) population. For obvious reasons, these hypothetical minor bodies are called inner-Earth objects (IEOs). While much progresses has been made in learning more about the Amor, Apollo, and Aten population from surveys optimized for their discovery, no large, systematic, and similar observation projects devoted to the search of IEOs have been started. For their own orbital nature, IEOs can be observed only at small solar elongations ( Keywords: Asteroids; Experimental techniques

lt has been suggested that phosphine ([PH.sub.3]) may contribute significantly to the microwave emission spectrum of Neptune, and to the centimeter-wavelength opacity measured by the Voyager 2 spacecraft at Neptune (D. R. DeBoer and P. G. Steffes 1996a, Icarus 123, 324-335). As a result, laboratory measurements of the microwave opacity and refractivity of [PH.sub.3] in an [H.sub.2]/He atmosphere have been conducted at 1.5 GHz (20 cm), 2.2 GHz (13.3 cm), 8.3 GHz (3.6 cm), 13.3 GHz (2.3 cm), and 21.6 GHz (1.4 cm) at pressures of 1, 3, and 5 bars at room temperature. Results indicate that current theories significantly understate the centimeter-wavelength opacity of [PH.sub.3]. This higher-than-expected opacity is likely due to a molecular inversion spectrum, of which no measurements have been reported. These results will elucidate the interpretation of centimeter-wavelength microwave observations from radio telescopes and spacecraft radio occultation measurements of the atmospheres of all four jovian planets. Key Words: abundances, atmospheres; atmospheres, composition; jovian planets; radio observations; spectroscopy.

Low-resolution spectrophotometry of Jupiter by Karkoschka (1994, Icarus 111, 174-192) revealed a weak apparent absorption feature in the spectrum of Jupiter at 920-940 nm. This is the wavelength of the strong 2[v.sub.1] + [v.sub.3] band of [H.sub.2]O, and Karkoschka tentatively identified the feature as jovian [H.sub.2]O absorption. If this spectral feature is indeed due to [H.sub.2]O absorption, it would offer the exciting possibility of monitoring the jovian [H.sub.2]O with visible band spectroscopy. This feature has been seen in previous low-resolution spectroscopy of Jupiter such as that of Woodman et al. (1979, Icarus 37, 73-83), but was not identified as jovian in origin because of uncertainties in extinction corrections for the very strong telluric [H.sub.2]O absorption. Cochran et al. (1995, Bull. Am. Astron. Soc. 27, 66) tentatively identified the feature as due to [NH.sub.3], an identification that was supported by further low-resolution spectrophotometry by Karkoschka (1998, Icarus 133, 134-146). Here we present high-resolution spectra (R = 155,000) of Jupiter using the 2dcoude spectrometer on the 2.7-m Harlan Smith Telescope at McDonald Observatory, in order to make a definitive identification of this absorption feature. Observations were obtained when Jupiter was near quadrature in order to Doppler shift potential jovian [H.sub.2]O features away from the corresponding telluric lines. We demonstrate conclusively that the absorption band identified by Karkoschka is not, in fact, due to [H.sub.2]O. We present further evidence that it is most likely to be an absorption band of [NH.sub.3]. We searched our spectra carefully to attempt to identify absorption lines which are actually due to [H.sub.2]O, without success. Key Words: Jupiter, atmosphere; spectroscopy; atmospheres, composition.