Feuchtgruber H, Lellouch E, de Graauw T, Bézard B, Encrenaz T, Griffin M
Max-Planck Institut für Extraterrestrische Physik, Garching, Germany.
Nature. 1997 Sep 11;389(6647):159-62. doi: 10.1038/38236.
The atmospheres of the giant planets are reducing, being mainly composed of hydrogen, helium and methane. But the rings and icy satellites that surround these planets, together with the flux of interplanetary dust, could act as important sources of oxygen, which would be delivered to the atmospheres mainly in the form of water ice or silicate dust. Here we report the detection, by infrared spectroscopy, of gaseous H2O in the upper atmospheres of Saturn, Uranus and Neptune. The implied H2O column densities are 1.5 x 10(15), 9 x 10(13) and 3 x 10(14) molecules cm(-2) respectively. CO2 in comparable amounts was also detected in the atmospheres of Saturn and Neptune. These observations can be accounted for by external fluxes of 10(5)-10(7) H2O molecules cm(-2) s(-1) and subsequent chemical processing in the atmospheres. The presence of gaseous water and infalling dust will affect the photochemistry, energy budget and ionospheric properties of these atmospheres. Moreover, our findings may help to constrain the injection rate and possible activity of distant icy objects in the Solar System.
巨行星的大气层具有还原性，主要由氢、氦和甲烷组成。但是环绕这些行星的光环和冰卫星，以及行星际尘埃流，可能成为重要的氧气来源，这些氧气将主要以水冰或硅酸盐尘埃的形式输送到大气层中。在此，我们报告通过红外光谱法在土星、天王星和海王星的高层大气中检测到气态水。其隐含的水汽柱密度分别为1.5×10¹⁵、9×10¹³和3×10¹⁴分子·厘米⁻²。在土星和海王星的大气层中还检测到了等量的二氧化碳。这些观测结果可以通过10⁵ - 10⁷个水分子·厘米⁻²·秒⁻¹的外部通量以及随后大气层中的化学过程来解释。气态水和下落尘埃的存在将影响这些大气层的光化学、能量平衡和电离层特性。此外，我们的发现可能有助于限制太阳系中遥远冰质天体的注入速率和可能的活动。
