School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA.
Astrobiology. 2009 Dec;9(10):965-78. doi: 10.1089/ast.2008.0316.
Phyllosilicates are hydrous minerals formed by interaction between rock and liquid water, and are commonly found in meteorites that originate in the asteroid belt. Collisions between asteroids contribute to zodiacal dust, which therefore reasonably could include phyllosilicates. Collisions between planetesimals in protoplanetary disks may also produce dust that contains phyllosilicates. These minerals possess characteristic emission features in the mid-infrared and could be detectable in extrasolar protoplanetary disks. We have determined whether phyllosilicates in protoplanetary disks are detectable in the infrared, using instruments such as those on board the Spitzer Space Telescope and the Stratospheric Observatory for Infrared Astronomy (SOFIA). We calculated opacities for the phyllosilicates most common in meteorites and, using a two-layer radiative transfer model, computed the emission of radiation from a protoplanetary disk. We found that phyllosilicates present at the 3% level lead to observationally significant differences in disk spectra and should therefore be detectable with the use of infrared observations and spectral modeling. Detection of phyllosilicates in a protoplanetary disk would be diagnostic of liquid water in planetesimals in that disk and would demonstrate similarity to our own Solar System. We also discuss use of phyllosilicate emission to test the "water worlds" hypothesis, which proposes that liquid water in planetesimals should correlate with the inventory of short-lived radionuclides in planetary systems, especially (26)Al.
层状硅酸盐是由岩石与液态水相互作用形成的含水矿物，常见于起源于小行星带的陨石中。小行星之间的碰撞会产生黄道尘，因此黄道尘中很可能含有层状硅酸盐。原行星盘中星子之间的碰撞也可能产生含有层状硅酸盐的尘埃。这些矿物在中红外波段具有特征发射特征，在系外原行星盘中可能是可探测的。我们使用斯皮策太空望远镜和平流层红外天文观测台 (SOFIA) 等仪器，确定了原行星盘中的层状硅酸盐在红外波段是否可探测。我们计算了陨石中最常见的层状硅酸盐的不透明度，并使用两层辐射传输模型计算了原行星盘辐射的发射。我们发现，含量为 3%的层状硅酸盐会导致盘光谱的观测差异显著，因此应该可以通过红外观测和光谱建模来探测到。在原行星盘中探测到层状硅酸盐将表明该盘中的星子中存在液态水，并且与我们自己的太阳系相似。我们还讨论了利用层状硅酸盐的发射来测试“水世界”假说的可行性，该假说提出行星系统中短寿命放射性核素（特别是 26Al）的丰度应与星子中的液态水相关。
