Atmospheric Circulation and Evolution of Short-Period Extrasolar Giant Planets

AST 0307664 Showman在其他恒星周围发现的巨行星中，有五分之一的行星与恒星的距离小于0.1天文单位。这些行星的小轨道增加了从地球上看它们过境恒星的可能性。其中一颗行星HD 209458 b已经被观测到每3.5天经过它的星星。当这颗行星从它的星星前面经过时，恒星的光线变暗，我们现在知道这颗行星的半径是木星的1.35倍。预计在未来几年内还会有数十次凌日探测，从而可以计算出更多行星的半径，并可能直接测量太阳辐射、昼夜温差和大气成分。 此外，定于2006年发射的开普勒使命任务应能推断出至少100个凌日热彗星的半径和半径。要了解这些测量结果，就需要了解可能的大气环流状况。昼夜温差取决于平流的速度（即，风）穿越地球。云的密度取决于云的形成位置，而可凝结物质（如硅酸盐或碱性化合物）的丰度则取决于环流的几何形状。此外，了解半径需要了解环流。半径代表了行星冷却和收缩的历史，这是通过环流对温度剖面，云丰度和内部能量传输的影响而受到环流的影响。HD209458b的演化模型使用现实的大气温度预测的半径太小，这表明计算中缺少一些热源。最好的假设是，大气热力发动机产生的动能被输送到内部，在那里抵消了导致行星收缩的能量损失。在这个项目中，亚利桑那大学的亚当·肖曼博士将研究大气环流和短周期行星（所谓的“热彗星”）的演变。Showman博士和合作者将对HD 209458 b的大气环流进行三维非线性数值模拟（和其他热行星），以确定（i）环流的性质，包括风速，昼夜温差和垂直结构，以及这些行星的红外光曲线，（ii）云形成的位置，的影响，并在整个地球上的空间变化，以及（iii）的幅度和深度的动能生产和耗散，这是至关重要的，在评估是否大气热机可以“膨胀”的半径HD209458b足以满足其测量值。这些模拟将与现有和即将进行的观测紧密联系在一起，并且是第一批研究动力学对这些行星可观测特性的影响的模拟之一。该项目的更广泛影响是：（一）将对太阳系外行星进行与模拟一致的图形可视化，以显示这些行星的可能样子。这些将用于公共和科学演示和采访，以增加公众对太阳系外行星的兴趣。(ii)研究结果将通过科学讲座、公开演讲和采访向科学界和公众广泛传播。(iii)一个研究生将完成这里描述的博士学位的工作。论文(iv)肖曼博士将利用这项研究来说明他所教授的研究生和本科生课程中发现的兴奋。

AST 0307664ShowmanOne fifth of the giant planets discovered around other stars are orbiting at distances less than 0.1 Astronomical Unit from their stars. These planets' small orbits increase the likelihood that they will transit their stars as viewed from Earth. One such planet, HD209458b, has already been observed to transit its star every 3.5 days. From the dimming of the stellar light as the planet passes in front of its star, we now know that the planet's radius is 1.35 times that of Jupiter. Dozens more transit detections are expected within the next several years, allowing additional planets' radii to calculated, and direct measurements of albedo, day-night temperature differences, and atmospheric composition are also likely. Furthermore, the Kepler mission, scheduled for launch in 2006, should allow the radii and albedos of at least 100 transiting hot Jupiters to be inferred. An understanding of these measurements will require knowledge of possible atmospheric circulation regimes. The day-night temperature difference depends on the speed of advection (i.e., winds) across the planet. The albedo depends on where clouds form, and the abundance of condensible species such as silicates or alkali compounds depends on the geometry of the circulation. Furthermore, understanding the radius will require knowledge of the circulation. The radius represents the planet's history of cooling and contraction, which is affected by the circulation through the circulation's influence ontemperature profile, cloud abundance, and internal energy transport. Evolution models of HD209458b that use realistic atmospheric temperatures predict a radius that is too small, which suggests that some heat source is missing from the calculations. The best hypothesis is that kinetic energy produced by the atmospheric heat engine is transported into the interior, where it counteracts the loss of energy that causes planetary contraction. In this project Dr. Adam Showman, University of Arizona, will investigate the atmospheric circulation and evolution of short-period planets (the so-called "hot Jupiters"). Dr. Showman and collaborators will conduct three-dimensional, nonlinear numerical simulations of the atmospheric circulation of HD209458b (and other hot Jupiters) to determine (i) the nature of the circulation, including wind speeds, day-night temperature differences, and vertical structure, with implications for the infrared light curve of these planets, (ii) locations of cloud formation, with implications for albedo and its spatial variation across the planet, and (iii) the magnitude and depth of kinetic energy production and dissipation, which is crucial in evaluating whether the atmospheric heat engine can "inflate" the radius of HD209458b enough to satisfy its measured value. The simulations will be tightly linked to existing and upcoming observations and are among the first to investigate the effects of dynamics on the observable properties of these planets. Broader impacts of the project are: (i) Graphic visualization of extrasolar planets will be performed,consistent with the simulations, to show what these planets may look like. These will be used in public and scientific presentations and interviews to increase public interest in extrasolar planets. (ii) The results of the research will be widely disseminated to the scientific community and general public through scientific talks, public presentations, and interviews. (iii) A graduate student will perform the work described here for a Ph.D. thesis. (iv) Dr. Showman will use the research to illustrate the excitement of discovery in the graduate and undergraduate courses that he teaches.***