The role of giant impacts in the formation of the outer solar system and exosystems

巨大撞击在外太阳系和系外系统形成中的作用

• 批准号: 2779906
• 金额: --
• 依托单位: University of Bristol
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2779906
• 关键词: role; giant; impacts; formation; outer

Project Background:Giant impacts (collisions between planet-sized bodies) are the most violent events in planet formation. For a few hours, collisions that form greater than Earth-mass bodies release more energy than the Sun. Large fractions of the icy and/or rocky mantles of the colliding bodies are melted and vaporised, and the huge torques exerted can leave the post-impact body rapidly rotating. The mass of the largest body may either increase or decrease, depending on the amount of material ejected from the system. Impacts can fundamentally alter the trajectory of a planet's evolution, as the ratios of atmosphere, crust, mantle and core all change and systems of moons can be formed. For example, giant impacts are thought to be responsible for the high obliquity of Uranus, the high density of Mercury, and the formation of Earth's Moon.The thermal and rotational states of post-impact bodies are so extreme that a significant fraction of impacts produce synestias, a recently theorisedclass of planetary object (Lock & Stewart, 2017). Synestias are bodies that exceed the corotation limit, defined as the angular momentum at which a planet's equatorial velocity equals that of a circular Keplerian orbit. Post-impact synestias are typically many times larger than cooler planets and form donut-shaped structures (Figure1). The different dynamical and thermodynamical states of synestias have significant implications for moon formation, core formation, and the distribution of volatiles within planets.Only a limited record of giant impacts remains in our solar system, but exoplanet observations are revolutionising this field. Recent space telescopes, such as Kepler and TESS, along with multiple ground-based surveys, are dramatically increasing the number of known exoplanets. Exosystems have a range of architectures and host planets with widely varying densities, and so bear witness to the many possible outcomes of giant impacts and planet formation in general. Furthermore, as we find more and more exoplanets and begin to observe planets around younger stars, we may soon detect planetary bodies in the immediate aftermath of giant impacts.Studies of giant impacts, with which these observations are interpreted, have largely focused on the impacts expected during formation of our inner solar system. There has been little work on collisions between more massive planets, even though such impacts could have helped shape the outer solar system. In addition, ours may not be a typical planetary system. It lacks the most common planets found around other stars: super-Earths and mini-Neptunes (planets with radii between Earth and Neptune). Many of these planets have large ice (e.g., water) and/or gas fractions. Few studies have explored impacts between more massive terrestrial and/or volatile-richbodies and, at present, we do not understand the outcome of what are likely the most frequent planetary collisions in the universe.Project Aims and MethodsThis project will explore how collisions shape the planets in our solar system and in exosystems. Using state-of-the-artgiantimpact simulations, the successful candidatewill investigate the range of dynamic and thermodynamic outcomes of collisions between water-rich bodies, and develop 'scaling laws' that relate the outcomes to the impact parameters. Although generally a common occurrence, the rates and energies of impacts vary between different planet formation models. By analysing the frequency and parameters of impacts in each scenario, the student will ascertain how giant impacts would sculpt planetary systems in different cases. Furthermore, by determining the observational signatures of post-impact bodies and synestias, the project will aim toprovide the tools necessary to identify...

项目背景：巨大的撞击（行星大小的天体之间的碰撞）是行星形成过程中最剧烈的事件。在几个小时内，形成比地球质量更大的天体的碰撞释放出比太阳还多的能量。碰撞体的大部分冰和/或岩石地幔被熔化和蒸发，所施加的巨大扭矩可以使撞击后的物体快速旋转。最大物体的质量可能会增加或减少，具体取决于从系统中喷射的材料量。撞击可以从根本上改变行星演化的轨迹，因为大气、地壳、地幔和地核的比例都会发生变化，卫星系统也会形成。例如，巨大的撞击被认为是造成天王星的高倾角、水星的高密度以及月球的形成的原因。撞击后天体的热状态和旋转状态非常极端，以至于很大一部分撞击会产生synestias，最近理论化的一类行星物体（Lock & Stewart，2017）。联内星是超过共转极限的天体，共转极限定义为行星赤道速度等于圆形开普勒轨道的角动量。撞击后的联丝体通常比温度较低的行星大很多倍，并形成环形结构（图1）。联星体的不同动力学和热力学状态对月球形成、核心形成以及行星内挥发物的分布具有重大影响。我们的太阳系中仅保留了有限的巨大撞击记录，但系外行星观测正在彻底改变这一领域。最近的太空望远镜，例如开普勒和苔丝，以及多次地面调查，正在急剧增加已知系外行星的数量。外系统具有一系列结构和密度差异很大的宿主行星，因此见证了巨大撞击和行星形成的许多可能结果。此外，随着我​​们发现越来越多的系外行星并开始观察年轻恒星周围的行星，我们可能很快就会在大撞击之后立即发现行星体。对这些观测结果进行解释的大撞击研究主要集中在撞击上预计在我们的内太阳系形成期间。尽管这种撞击可能有助于塑造外太阳系，但关于更大质量行星之间碰撞的研究却很少。此外，我们的行星系统可能不是一个典型的行星系统。它缺乏在其他恒星周围发现的最常见的行星：超级地球和迷你海王星（半径在地球和海王星之间的行星）。许多这些行星都有大量的冰（例如水）和/或气体成分。很少有研究探索更大质量的地球和/或富含挥发性天体之间的影响，目前，我们还不了解宇宙中最频繁的行星碰撞的结果。项目目标和方法该项目将探索碰撞如何塑造地球我们太阳系和系外系统中的行星。使用最先进的巨型撞击模拟，成功的候选人将研究富含水体之间碰撞的动力学和热力学结果的范围，并制定将结果与撞击参数联系起来的“缩放定律”。尽管通常发生的情况很常见，但不同行星形成模型的撞击速度和能量有所不同。通过分析每种情况下撞击的频率和参数，学生将确定巨大的撞击在不同情况下如何塑造行星系统。此外，通过确定撞击后物体和联体的观测特征，该项目旨在提供必要的工具来识别……