Scientific rationale for Saturn׳s in situ exploration

Remote sensing observations meet some limitations when used to study the bulk atmospheric composition of the giant planets of our solar system. A remarkable example of the superiority of in situ probe measurements is illustrated by the exploration of Jupiter, where key measurements such as the determination of the noble gases׳ abundances and the precise measurement of the helium mixing ratio have only been made available through in situ measurements by the Galileo probe. This paper describes the main scientific goals to be addressed by the future in situ exploration of Saturn placing the Galileo probe exploration of Jupiter in a broader context and before the future probe exploration of the more remote ice giants. In situ exploration of Saturn׳s atmosphere addresses two broad themes that are discussed throughout this paper: first, the formation history of our solar system and second, the processes at play in planetary atmospheres. In this context, we detail the reasons why measurements of Saturn׳s bulk elemental and isotopic composition would place important constraints on the volatile reservoirs in the protosolar nebula. We also show that the in situ measurement of CO (or any other disequilibrium species that is depleted by reaction with water) in Saturn׳s upper troposphere may help constraining its bulk O/H ratio. We compare predictions of Jupiter and Saturn׳s bulk compositions from different formation scenarios, and highlight the key measurements required to distinguish competing theories to shed light on giant planet formation as a common process in planetary systems with potential applications to most extrasolar systems. In situ measurements of Saturn׳s stratospheric and tropospheric dynamics, chemistry and cloud-forming processes will provide access to phenomena unreachable to remote sensing studies. Different mission architectures are envisaged, which would benefit from strong international collaborations, all based on an entry probe that would descend through Saturn׳s stratosphere and troposphere under parachute down to a minimum of 10 bar of atmospheric pressure. We finally discuss the science payload required on a Saturn probe to match the measurement requirements.

Scientific Rationale of a Saturn Probe Mission

We describe the main scientific goals to be addressed by future in situ exploration of Saturn.

Molecular nitrogen in comet 67P/Churyumov-Gerasimenko indicates a low formation temperature

Molecular nitrogen (N2) is thought to have been the most abundant form of nitrogen in the protosolar nebula. It is the main N-bearing molecule in the atmospheres of Pluto and Triton and probably the main nitrogen reservoir from which the giant planets formed. Yet in comets, often considered the most primitive bodies in the solar system, N2 has not been detected. Here we report the direct in situ measurement of N2 in the Jupiter family comet 67P/Churyumov-Gerasimenko, made by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis mass spectrometer aboard the Rosetta spacecraft. A N2/CO ratio of Embedded Image (2σ standard deviation of the sampled mean) corresponds to depletion by a factor of ~25.4 ± 8.9 as compared to the protosolar value. This depletion suggests that cometary grains formed at low-temperature conditions below ~30 kelvin.

Time variability and heterogeneity in the coma of 67P/Churyumov-Gerasimenko

Comets contain the best-preserved material from the beginning of our planetary system. Their nuclei and comae composition reveal clues about physical and chemical conditions during the early solar system when comets formed. ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) onboard the Rosetta spacecraft has measured the coma composition of comet 67P/Churyumov-Gerasimenko with well-sampled time resolution per rotation. Measurements were made over many comet rotation periods and a wide range of latitudes. These measurements show large fluctuations in composition in a heterogeneous coma that has diurnal and possibly seasonal variations in the major outgassing species: water, carbon monoxide, and carbon dioxide. These results indicate a complex coma-nucleus relationship where seasonal variations may be driven by temperature differences just below the comet surface.

Cometary Isotopic Measurements

Isotopic ratios in comets provide keys for the understanding of the origin of cometary material, and the physical and chemical conditions in the early Solar Nebula. We review here measurements acquired on the D/H, N-14/N-15, O-16/O-18, C-12/C-13, and S-32/S-34 ratios in cometary grains and gases, and discuss their cosmogonic implications. The review includes analyses of potential cometary material available in collections on Earth, recent measurements achieved with the Herschel Space Observatory, large optical telescopes, and Rosetta, as well as recent results obtained from models of chemical-dynamical deuterium fractionation in the early solar nebula. Prospects for future measurements are presented.

HIV disclosure decisions and social support among African-American women in Houston, Texas

African Americans make up 12.3% of the population but account for over half of the new HIV cases and 39% of the AIDS cases in 2003 (Centers for Disease Control and Prevention [CDC], 2003). African American women in particular accounted for 64% of these cases of HIV and 60% of the AIDS cases (Leigh & Huff, 2003). This study contributed to the knowledge about the disclosure process of women living with HIV/AIDS by documenting the relationship between social support and the disclosure process in the African American HIV/AIDS population.^ The study aims were to: (1) discuss the participants' self concept of support; (2) describe the common characteristics of the disclosure process; and (3) evaluate the common characteristics of support sought in a potential disclosure source. The ethnographic qualitative methodology was utilized to elicit participant narratives of HIV disclosure and social support. The researcher utilized a key informant interview methodology building on existing social and organizational relationships (Krueger, 1994) to gain access to the population. ^ Semi-structured interviews are a widely used and accepted qualitative research method for use with hard to reach populations and sensitive topics. Ten participants completed a 45 to 60 minute, one on one semi-structured interview covering social support and disclosure variables. Inclusion and exclusion criteria included: (1) self identified as a person living with HIV/AIDS; (2) African American); (3) female; (4) age 18-64 years old, (5) residence in Houston or surrounding counties.^ Themes generated from the interviews were (1) nondisclosure, (2) experiences with disclosure, (3) timing, (4) disclosure sources, and (5) coping. The themes suggest African American women living with HIV/AIDS come from different lifestyles but share similar experiences. Women utilize different strategies such as deciphering whom to trust and determining how much information to divulge in order to protect themselves or others.^ Although the sample group was small for this study, the results inform us about the various experiences each woman goes through as it relates to social support and disclosure and that each woman has to customize her response to the type of support she is receiving and her personal attitude about her disease.^