Comet spectrum

The recent close-encounter, especially with comet Hale-Bopp, focused the attention of the ground-based telescopes in all regions of the electromagnetic spectrum to produce the molecular inventory shown in Table 6.4. Chemical network models for... 

Spectra of comet Hale-Bopp, showing features attributable to silicate minerals, (a) Profile of fine structure in the 10 silicate emission feature a peak at 11.2 and a shoulder at 11.9 are due to olivine, and a slope change at 9.2 results from pyroxene, (b) Expanded infrared spectrum exhibiting a number of sharp peaks due to magnesian olivine and pyroxene. The region of (a) is bounded by a small box. Modified from Crovisier et al. (2000) and Hanner and Bradley (2003). 

The ground state C1(Xl L ) is a primary product of acetylene photolysis. The r/ ll state is formed from the photolysis of bromoacetylene in the vacuum ultraviolet. It is also formed in flame and discharges through carbon containing compounds. The Swan system is a major feature of emission spectrum from the heads of comets. 

Figure 6.5 Comparison of the 10 pm Si-O stretching bands of a GEMS-rich IDP and astronomical silicates. (A) Chondritic IDP L2008V42A. Profile derived from transmittance spectrum. (B) Comet Halley (Campins Ryan 1989). (C) Comet Hale-Bopp (Hayward et al. 2000). (D) Late-stage Herbig Ae/Be star HD 163296 (Sitko et al. 1999). The structure at 9.5 qm in (B), (C), and (D) is due to telluric O3. Figure from Bradley et al. (1999).

Ultraviolet spectra of Comet Seargent 1978 XV taken from the lUE satellite. Exposure times for the low-resolution spectra are 180 and 165 min. The high-resolution spectrum shows the rotational structure of the (0,0) OH band (from Jackson, W. M., Icarus 41, 147, 1980)... 

Two stable molecules which can be regarded as primary constituents of the nucleus were identified in the microwave spectrum of Comet Kohoutek, namely HCN at 3.4 mm (Huebner et al. and CHjCN at 2.7 mm (Ulich and Conclin Up to now these identifications could not be repeated in other comets. Production rates are estimated to be some 10 mol/s at 1 a. u., in the range of the visual radicals. The search for these molecules and also for CO which had been detected in the UV spectrum of Comet West was unsuccessful in Comet Bradfield 1978 VII, probably because the production rates of this comet were lower (F. P. Schioerb et al. Upper limits for the column density of HCN and CH3CN were less than those derived for Kohoutek, while the upper limit for the CO production was comparable to that inferred from Comet West. Also the very important detection of the 1.35 cm line of HjO in Comet Bradfield 1974 III by Jackson et al. has not yet been confirmed in other comets. 

The 3.2-3.6 p emission band is observed with moderate spectral resolution in some comets. This band is the signature of both aliphatic and aromatic unsaturated carbonaceous compounds. In particular, the 3.28 p band is cliaracter-ized by aromatics. Moreels et al. [26] identified phenanthrene in the recorded visible spectrum of comet Halley. 

Comet assay 3D human reconstructed skin models DNA damage in cells or tissues Broad spectrum of damage Genotoxicity hazard identification... 

Today astronomers routinely study the chemical composition of a planet by analyzing sunlight reflected off its surface and atmosphere. The same method is used to analyze the chemical composition of other bodies in the solar system, such as comets, meteors, and planetary satellites. This process is challenging since, in some cases, relatively modest amounts of light are reflected from a planet or other body. Also, the spectrum observed is likely to be very complex, with the lines of many elements and compounds present in the pattern. 

Noble gases are intrinsically difficult to detect by spectroscopy. For example, solar photospheric spectra, which form the basis for solar abundance values of most elements, do not contain lines from noble gases (except for He, but this line cannot be used for abundance determinations). Yet, ultraviolet spectroscopy is the only or the major source of information on noble gas abundances in the atmospheres of Mercury and comets. In the Extreme Ultraviolet (EUV), photon energies exceed bond energies of molecules and the first ionization potential of all elements except F, He, and Ne, so that only these elements are visible in this part of the spectrum (Krasnopolsky et al. 1997). Other techniques can be used to determine the abundance of He where this element is a major constituent. Studies of solar oscillations (helioseismology) allow a precise determination of the He abundance in the solar interior, and the interferometer on the Galileo probe yielded a precise value for the refractive index and hence the He abundance in the upper atmosphere of Jupiter (see respective sections of this chapter). 

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