First detection of the 63 μm atomic oxygen line in the thermosphere of Mars with GREAT/SOFIA
First detection of the 63 μm atomic oxygen line in the thermosphere of Mars with GREAT/SOFIA
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DOI：
10.1051/0004-6361/201526377
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发表时间：
2015-08-01
影响因子：
6.5
通讯作者：
Honingh, N.
中科院分区：
文献类型：
--
作者：
Rezac, L.;Hartogh, P.;Honingh, N.
上下文平流层红外天文观测台（索菲亚）及其2.5米望远镜为远红外波长范围内行星大气的光谱观测提供了新的科学机会。本文介绍了2014年5月14日使用德国太赫兹天文接收器（GREAT）仪器在4.7 THz下对火星大气进行观测的第一批结果。原子氧63 μ m的过渡，OI，在对火星连续吸收检测，具有高的信号噪声比（类似于35）。采用全球环流模式的束流平均氧原子作为输入，对观测线区域的辐射传输进行模拟，并采用网格搜索法得到了柱密度的新估计。在最小二乘意义上，最小化计算和观察到的谱线强度之间的差异，得到原子氧柱密度为（1.1 +/- 0.2）x 10（17）cm（2）。这个数值大约是现代火星光化学模型预测的两倍。辐射传输模拟结果表明，该谱线形成于70-120 km的高空大气区。首次在火星大气中探测到原子氧谱线的远红外跃迁。吸收深度提供了柱密度的估计，这种测量提供了额外的手段来约束全球环流模型和气辉研究中的光化学模型。由于缺乏监测火星高层大气中原子氧的其他手段，索菲亚天文台今后的观测非常可取。
Context. The Stratospheric Observatory for Infrared Astronomy (SOFIA) with its 2.5 m telescope provides new science opportunities for spectroscopic observations of planetary atmospheres in the far-infrared wavelength range.Aims. This paper presents first results from the 14 May, 2014 observing campaign of the Martian atmosphere at 4.7 THz using the German REceiver for Astronomy at Terahertz frequencies (GREAT) instrument.Methods. The atomic oxygen 63 mu m transition, OI, was detected in absorption against the Mars continuum, with a high signal-to-noise ratio (similar to 35). A beam-averaged atomic oxygen from a global circulation model was used as input to the radiative transfer simulations of the observed line area and to obtain a new estimate on the column density using a grid-search method.Results. Minimizing differences between the calculated and observed line intensities in the least-square sense yields an atomic oxygen column density of (1.1 +/- 0.2) x 10(17) cm(2). This value is about twice as low as predicted by a modern photochemical model of Mars. The radiative transfer simulations indicate that the line forms in the upper atmospheric region over a rather extended altitude region of 70-120 km.Conclusions. For the first time, a far-infrared transition of the atomic oxygen line was detected in the atmosphere of Mars. The absorption depth provides an estimate on the column density, and this measurement provides additional means to constrain the photochemical models in global circulation models and airglow studies. The lack of other means for monitoring the atomic oxygen in the Martian upper atmosphere makes future observations with the SOFIA observatory highly desirable.