EPOXI: Comet 103P/Hartley 2 Observations from a Worldwide Campaign

in Astrophysical Journal (2011), 734(Letters), 11-9

Earth- and space-based observations provide synergistic information for space mission encounters by providing data over longer timescales, at different wavelengths and using techniques that are impossible ... [more ▼]

Earth- and space-based observations provide synergistic information for space mission encounters by providing data over longer timescales, at different wavelengths and using techniques that are impossible with an in situ flyby. We report here such observations in support of the EPOXI spacecraft flyby of comet 103P/Hartley 2. The nucleus is small and dark, and exhibited a very rapidly changing rotation period. Prior to the onset of activity, the period was ~16.4 hr. Starting in 2010 August the period changed from 16.6 hr to near 19 hr in December. With respect to dust composition, most volatiles and carbon and nitrogen isotope ratios, the comet is similar to other Jupiter-family comets. What is unusual is the dominance of CO[SUB]2[/SUB]-driven activity near perihelion, which likely persists out to aphelion. Near perihelion the comet nucleus was surrounded by a large halo of water-ice grains that contributed significantly to the total water production. [less ▲]

H[SUB]2[/SUB] temperature and self-absorption: analysis of Jovian auroral spectra obtained with the FUSE satellite

in Bulletin of the American Astronomical Society (2001, November 01)

High-resolution spectra of the Jovian aurora have been obtained with unprecedented spectral resolution in the 900-1190 Ì· window with the the Far Ultraviolet Spectroscopic Explorer (FUSE), using the 30 ... [more ▼]

High-resolution spectra of the Jovian aurora have been obtained with unprecedented spectral resolution in the 900-1190 Ì· window with the the Far Ultraviolet Spectroscopic Explorer (FUSE), using the 30"x30" LWRS aperture. All observed features belong to the H[SUB]2[/SUB] transitions from the B, C, B', D, B" and D' electronic states to the ground-state. These emissions are excited by inelastic collisions of the primary and secondary auroral electrons with H[SUB]2[/SUB] molecules. The relative intensity distribution of the observed lines depends on the rotational temperature of the emitting layer and self-absorption. Below 1100 Ì· , the transitions leading to the v" = 0, 1 and 2 levels of ground-state are partially or totally absorbed by H[SUB]2[/SUB], giving indications about the vibrational H[SUB]2[/SUB] distribution and overlying column. After a validation with an unabsorbed and a self-absorbed laboratory spectrum obtained in controlled conditions (100K, 300 eV), this study compares the observations and synthetic spectra, generated by a code including the B, C and B', D, B" and D' Rydberg states. The rotational and vibrational H[SUB]2[/SUB] temperatures are determined as well as the overlying H[SUB]2[/SUB] column. The combination of these parameters is used to determine the depth of the auroral energy deposition. This work is based on data obtained for the Guaranteed Time Team by the NASA-CNES-CSA FUSE mission operated by the Johns Hopkins University. French participants are supported by CNES. Financial support to U.S. participants has been provided by NASA contract NAS5-32985. [less ▲]