Atmospheres and Climates of Exoplanets

系外行星的大气和气候

• 批准号: RGPIN-2014-03844
• 负责人: Menou, Kristen
• 金额: $ 3.28万
• 依托单位: University of Toronto
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2014
• 资助国家: 加拿大
• 起止时间: 2014-01-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=566126
• 关键词: Atmospheres; Climates; Exoplanets

In recent years, the study of exoplanets has shifted from their detection to the characterization of their physical properties, in particular their atmospheres. The work on exoplanets proposed here consists of using some of the basic tools and principles of atmospheric science, originally developed for Earth, to deepen our understanding of the diversity of atmospheric behaviors expected on exoplanets and to clarify how those might shape astronomical observables. 1) Hot Exoplanets Hot Jupiters/Saturns/Neptunes form the best characterized class of exoplanets and the next generation of astronomical observatories and surveys, such as TESS, JWST and ECho, will yield a wealth of new data on these planets over the next decade. Recently, it became clear that new physics in the form of magnetic induction plays an important role in the weakly-ionized atmospheres of many such planets, when temperatures exceed about 1300 K, leading to magnetic drag on the atmospheric winds and ohmic dissipation at depth (which results in radius inflation for these planets). Using a combination of analytical considerations and numerical models, we will focus our research program for this class of exoplanets on three specific topics designed to further test and consolidate the magnetic induction scenario. We will clarify expected trends for magnetic drag and ohmic dissipation with planet temperature for the ensemble population of known planets, which should be manifest given the exponential dependence of atmospheric ionization with temperature. For specific, well characterized planets, we will also explore the interplay between several planetary observables which are directly impacted by magnetic induction, such as dragged winds vs. the degree of radius inflation. Finally, we will study the possible role of an MHD runaway convergence of electric currents on the hot dayside to locally increase heating in those regions, a process which could be at the origin of the thermal inversions observationally inferred on several hot Jupiters. 2) Habitable worlds around M-dwarfs Terrestrial exoplanets orbiting in the habitable zone of low-mass M-dwarf stars are the focus of astronomical searches because several biases favor their detection and characterization. They may thus offer the first targets for atmospheric characterization of nearby habitable worlds in the next decade. Studying the rich climate dynamics of such worlds is important, to guide observational efforts and to provide an interpretation of the data when it becomes available. The use of adapted climate models to evaluate surface conditions on such remote worlds with permanent day and night sides is our preferred approach, given the inherent complexity of the climate system. Our work uses an advanced, yet versatile, Earth-system climate simulator, with a full hydrological cycle, adjustable land/ocean fractions and diagnostic cloud prescriptions, to study the climates of habitable worlds around M-dwarfs. A focus of our work on this class of planets will be to understand their unusual hydrological cycle, with the likely trapping of the majority of their surface water in the form of nightside ice (water-trapped climate configuration). The amount of residual water left on the dayside of such planets will be an important factor determining the habitability of these worlds. More generally, our work will explore a variety of expected orbital configurations for such planets (spin rate, eccentricity, obliquity, asynchronism) and their consequences for the climate. Throughout this exploration, we will strive to quantify to what extent surface conditions and habitability can be inferred from the set of astronomical measurements that will be available to characterize such planets.

近年来，对系外行星的研究已经从探测转向表征其物理特性，特别是其大气层。这里提出的系外行星工作包括使用最初为地球开发的一些大气科学的基本工具和原理，以加深我们对系外行星上预期的大气行为多样性的理解，并澄清这些可能如何影响天文观测。 1) 热系外行星 热木星/土星/海王星构成了最具有特征的系外行星类别，下一代天文观测和调查，如 TESS、JWST 和 Echo，将在未来十年内产生大量有关这些行星的新数据。最近，人们发现，当温度超过约 1300 K 时，磁感应形式的新物理学在许多此类行星的弱电离大气中发挥着重要作用，导致大气风的磁阻力和深度欧姆耗散（从而导致这些行星的半径膨胀）。结合分析考虑和数值模型，我们将把此类系外行星的研究计划集中在三个特定主题上，旨在进一步测试和巩固磁感应场景。我们将阐明已知行星总体中磁阻力和欧姆耗散随行星温度变化的预期趋势，考虑到大气电离与温度的指数依赖性，这一趋势应该是显而易见的。对于特定的、特征良好的行星，我们还将探索几个直接受磁感应影响的行星可观测值之间的相互作用，例如拖曳风与半径膨胀程度。最后，我们将研究热日侧电流的 MHD 失控收敛对局部增加这些区域的加热的可能作用，这一过程可能是在几个热木星上观测推断的热逆温的起源。 2）M型矮星周围的宜居世界 在低质量M型矮星的宜居带中运行的类地系外行星是天文学搜索的焦点，因为一些偏见有利于它们的探测和表征。因此，它们可能为未来十年附近宜居世界的大气特征提供第一个目标。研究这些世界丰富的气候动态非常重要，可以指导观测工作并在获得数据时提供对数据的解释。考虑到气候系统固有的复杂性，使用适应的气候模型来评估这种具有永久白天和黑夜的偏远世界的表面条件是我们的首选方法。我们的工作使用先进且多功能的地球系统气候模拟器，具有完整的水文循环、可调节的陆地/海洋部分和诊断云处方，来研究 M 矮星周围宜居世界的气候。我们对这类行星的工作重点是了解它们不寻常的水文循环，它们的大部分地表水可能以夜面冰的形式被困住（水困气候配置）。这些行星白天的残留水量将是决定这些行星宜居性的重要因素。更一般地说，我们的工作将探索此类行星的各种预期轨道配置（自转速率、偏心率、倾斜度、异步性）及其对气候的影响。在整个探索过程中，我们将努力量化可以在多大程度上从可用于表征此类行星的天文测量中推断出表面条件和宜居性。