类月卫星对类地行星轨道红外线曲线的影响
The Effect of Lunar-like Satellites on the Orbital Infrared Light Curves of Earth-analog Planets
摘要：
我们研究了类月卫星对类地太阳系外行星红外轨道光变曲线的影响。这样的光变曲线将由NASA的类地行星探测器（TPF）和欧空局的达尔文任务获得，作为重复观测的结果，以确认一个假定的行星的伴星状态。我们使用的能量平衡模型来计算磁盘平均红外（测热）通量从行星卫星系统在一个完整的轨道周期（一年）。这些卫星被认为缺乏大气层，具有像月球一样的低热惯性，并且跨越一系列合理的半径。行星被假定有热和轨道性质，模仿地球，而他们的行星和轨道半径的劣合仍然是自由参数。即使行星的总体热特性可以独立地受到限制（例如通过光谱学或来自表面海洋的镜面反射的可见波长检测），也只有最大的（大约火星大小）类月卫星可以通过类似TPF的仪器（即在红外波长处达到10-20的光度学信噪比的仪器）的光变曲线数据来检测。未探测到类月卫星会混淆对特定系统的红外线曲线的解释，因此它可能类似于一个具有高密度、相对于下合点的春分轨道经度不同以及在某些情况下热特性截然不同的单一行星。如果这颗行星的热性质不能独立确定，那么就不能从红外数据推断出类似月球的卫星的存在，从而表明光变曲线只能用于太阳系外类地行星的初步研究。
英文摘要：
We investigate the influence of lunar-like satellites on the infrared orbital light curves of Earth-analog extra-solar planets. Such light curves will be obtained by NASA's Terrestrial Planet Finder (TPF) and ESA's Darwin missions as a consequence of repeat observations to confirm the companion status of a putative planet. We use an energy balance model to calculate disk-averaged infrared (bolometric) fluxes from planet-satellite systems over a full orbital period (one year). The satellites are assumed to lack an atmosphere, have a low thermal inertia like that of the Moon and span a range of plausible radii. The planets are assumed to have thermal and orbital properties that mimic those of the Earth while their obliquities and orbital longitudes of inferior conjunction remain free parameters. Even if the gross thermal properties of the planet can be independently constrained (e.g. via spectroscopy or visible-wavelength detection of specular glint from a surface ocean) only the largest (approximately Mars-size) lunar-like satellites can be detected by light curve data from a TPF-like instrument (i.e. one that achieves a photometric signal-to-noise of 10-20 at infrared wavelengths). Non-detection of a lunar-like satellite can obfuscate the interpretation of a given system's infrared light curve so that it may resemble a single planet with high obliquity, different orbital longitude of vernal equinox relative to inferior conjunction and in some cases drastically different thermal characteristics. If the thermal properties of the planet are not independently established then the presence of a lunar-like satellite cannot be inferred from infrared data, thus demonstrating that photometric light curves alone can only be used for preliminary study of extra-solar Earth-like planets.
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