Saturn Helium Abundance: A Reanalysis of Voyager Measurements
Saturn Helium Abundance: A Reanalysis of Voyager Measurements
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土星氦丰度：对 Voyager 测量的重新分析
DOI：
10.1006/icar.1999.6265
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发表时间：
2000
期刊：
影响因子：
3.2
通讯作者：
D. Gautier
中科院分区：
文献类型：
--
作者：
B. Conrath;D. Gautier
利用旅行者木星射电掩星(RSS)计算的热发射光谱与旅行者红外光谱仪(IRIS)测量的光谱不一致，该温度分布重新定标为伽利略探测器的氦丰度值。亮度温度中的∼2K偏移量表明可能存在尚未确定的系统误差源。这引发了用同样的RSS-IRIS方法确定的旅行者号土星氦丰度的有效性的问题。我们通过开发一种仅从IRIS光谱同时反演温度、对氢分数和氦丰度的反演算法来解决这个问题。这种方法不能成功地应用于木星，因为光谱的低频端附近有强烈的气态NH3和云层不透明，但在土星温度较低的情况下，这种限制不那么严重。将该算法应用于土星光谱，得到体积混合比He/H2在0.11和0.16之间，对应于相对于土星大气中总氦和氢的氦质量分数Y=0.18-0.25。虽然这些反演依赖于对反演算法中的解的主观过滤，以减小氦值的非唯一性范围，但它们强烈建议He/H2的值明显大于Conrath等人先前获得的0.034±0.024的值。(Conrath，B.J.，D.Gautier，R.A.Hanel和J.S.Hornstein，1984，占星学。J.282,807-815)。
Thermal emission spectra calculated using Voyager Jupiter radio occultation (RSS) temperature profiles rescaled to the Galileo probe value of the helium abundance do not agree with the spectra measured by the Voyager infrared spectrometer (IRIS). The ∼2 K offset in brightness temperature suggests the possibility of a systematic error source yet to be identified. This raises the question of the validity of the Voyager Saturn helium abundance that was determined using the same RSS–IRIS approach. We address this issue by developing an inversion algorithm for the simultaneous retrieval of the temperature, the para H2 fraction, and the helium abundance from the IRIS spectra alone. This approach can not be successfully applied to Jupiter because of strong gaseous NH3 and cloud opacity near the low-frequency end of the spectrum, but this restriction is less severe at the lower temperatures of Saturn. Applications of the algorithm to Saturn spectra yield a volume mixing ratio He/H2 between 0.11 and 0.16 corresponding to a helium mass fraction relative to the total helium and hydrogen in Saturn's atmosphere of Y=0.18–0.25. Although these retrievals depend on subjective filtering of the solutions in the inversion algorithm to reduce the range of non-uniqueness for the helium values, they strongly suggest a value for He/H2 significantly larger than the value of 0.034±0.024 previously obtained by Conrath et al. (Conrath, B. J., D. Gautier, R. A. Hanel, and J. S. Hornstein 1984, Astrophys. J.282, 807–815) using the RSS–IRIS method.