Scientific objectives and observational requirements of spectrometers for main belt Comet 133P/Elst-Pizarro exploration

Abstract

The discoveries of main belt comets (MBC) in early twentieth century have attracted great interests of the planetary society, as the water ice and other volatile rich MBCs are located in the main belt and thus may have played a fundamental role in supplying waters to the early Earth. Therefore, MBCs are very interesting and important candidate objects for near future deep space exploration missions. We first summarize the scientific objectives of visible and infrared spectrometers for a flyby mission. Then we propose the major technical specifications for the spectrometers, based on the optical and thermal properties of one of the major targets, 133P/Elst-Pizarro. Our proposed spectral coverage is from 0.4 to 50 μm, which is realized by two spectrometers covering 0.4-5 μm and 5-50 μm, respectively. Visible and infrared imaging spectrometer (VIIS) is a grating spectrometer covering 0.4 to 5 μm with a spectral resolution of 5 nm in the VIS/NIR band and 10 nm in the SWIR/MWIR band. The spatial resolution of the VIIS is 0.5 m at an observational distance of 5 km. The signal to noise ratio of the spectrometer is better than 100 using cryogenic optics technology. Thermal emission spectrometer (TES) is a time modulated Fourier transform spectrometer which covers5-50 μmby one single interferometer. The spectral resolution of TES is 8 cm-1. The spatial resolution of TES is 10 m at an observational distance of 5 km.