A Programme of Research in Planetary Science at Leeds

利兹行星科学研究计划

基本信息

批准号：
ST/T000279/1
负责人：
John Plane
金额：
$ 74.19万
依托单位：
University of Leeds
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2020
资助国家：
英国
起止时间：
2020 至无数据
项目状态：
未结题

来源：
https://gtr.ukri.org/projects?ref=ST%2FT000279%2F1
关键词：
Programme Research Planetary Science Leeds

项目摘要

The two projects proposed here will investigate the upper atmospheres of Mars and Venus, with a focus on the impacts of cosmic dust particles. The dust originates from two sources: the asteroid belt between Mars and Jupiter, and comets which are dust-laden balls of ice that evaporate as they orbit towards the sun. Around 3 tonnes of dust enters Mars' atmosphere every 24 hrs; the input for Venus is around 46 tonnes. The dust enters at hyperthermal speeds, and so a fraction of the particles heat sufficiently to melt and evaporate. This process of meteoric ablation injects a variety of metals such as Fe, Mg and Na at around 80 km on Mars and 115 km on Venus, giving rise to layers of metal atoms and ions.Although the corresponding layers in the Earth's atmosphere have been studied for decades, it is only in the past 4 years that metals layers were first observed in another planetary atmosphere: NASA's MAVEN spacecraft arrived at Mars in late 2014 and has measured a range of metallic ions and atoms. Moreover, just after MAVEN reached Mars, a comet from the Oort Cloud narrowly avoided colliding with the planet. The result of the "fly-by" was the injection of around 80 tonnes of dust in only 3 hours, leading to huge quantities of metallic species being observed by MAVEN. Initially the dust was injected in only one hemisphere of the planet, and the resulting metals spread much more rapidly - both horizontally and vertically - than expected.MAVEN is also in a highly elliptical orbit, and as it approaches Mars it can make a "deep dip" down as far as only 120 km above the surface. This has produced a unique dataset which throws up several surprises. For example, the metallic ions would be expected to separate according to mass with the lighter ions being relatively more abundant higher in the atmosphere - but this is clearly not the case. There are also surprising differences in the atmospheric chemistry of these metals compared with the Earth: their diurnal variation seems to be controlled by atmospheric tides rather than photochemistry; and neutral metal atoms occur at unexpectedly low abundances in the CO2-rich atmosphere of Mars.In the first project we will explore these observations through a global atmospheric model of Mars which includes meteoric ablation and full descriptions of the metal chemistry based on laboratory studies of over 70 relevant reactions of Na, Fe and Mg species. The model will then be used to simulate the cometary flyby.The second project will examine the phenomenon of high-lying clouds in the atmospheres of these planets. Their terrestrial counterparts, known as noctilucent clouds, are H2O-ice clouds which occur around 83 km at high latitudes in summer. On Mars, clouds have been observed between 70 and 100 km, and in contrast mostly occur at equatorial latitudes. Furthermore, they are CO2-ice clouds. A major challenge has been to explain how these clouds can form, since the temperatures are hardly ever low enough for CO2 to condense on metal silicate particles. However, a promising candidate - proposed in a recent paper by the applicants - is that the meteor-ablated metals turn into metal carbonates, which absorb H2O to form "dirty ice" particles and these are effective seeds for CO2 ice. This will now be tested in the laboratory.In the case of Venus, we have the first tentative reports of a layer of clouds periodically appearing around 85 - 90 km i.e. well above the thick sulphuric acid clouds which envelop the entire planet up to around 70 km. In this project we will test experimentally our hypothesis that these detached clouds result from sulphuric acid droplets absorbing H2O and becoming dilute enough to freeze. Higher still around 120 km, the temperature falls far enough for CO2 ice clouds to form in the same way as on Mars. We will therefore model the likely visibility of these clouds, while our project partners search for the clouds using the Venus Express spacecraft.

这里提出的两个项目将研究火星和金星的上层大气，重点是宇宙灰尘颗粒的影响。灰尘来自两个来源：火星和木星之间的小行星带，而彗星是充满灰尘的冰球，当它们向太阳绕而蒸发时。大约3吨灰尘每24小时进入火星的气氛；金星的输入约为46吨。灰尘以高温的速度进入，因此颗粒的一小部分加热以融化和蒸发。 This process of meteoric ablation injects a variety of metals such as Fe, Mg and Na at around 80 km on Mars and 115 km on Venus, giving rise to layers of metal atoms and ions.Although the corresponding layers in the Earth's atmosphere have been studied for decades, it is only in the past 4 years that metals layers were first observed in another planetary atmosphere: NASA's MAVEN spacecraft arrived at Mars 2014年底，已经测量了一系列金属离子和原子。此外，在Maven到达火星之后，Oort云的一颗彗星狭窄地避免了与地球相撞。 “飞行”的结果是在仅3个小时内注射约80吨灰尘，从而导致Maven观察到大量金属物种。最初，将灰尘注射仅在地球的一个半球中，而所产生的金属在水平和垂直方面的蔓延得多，都比预期的。Maven也位于高度椭圆形的轨道中，并且随着它接近火星，它可以使“深浸”仅在表面上方120公里。这产生了一个独特的数据集，引发了几个惊喜。例如，金属离子有望根据质量分离，而较轻的离子在大气中相对较高 - 但这显然不是这种情况。与地球相比，这些金属的大气化学性质也存在令人惊讶的差异：它们的昼夜变化似乎是通过大气潮而不是光化学控制的。中性金属原子在MAR的二氧化碳大气中出现意外的低丰度出现。在第一个项目中，我们将通过MARS的全球大气模型探索这些观察结果，其中包括气象消融和基于70多种Na，Fe和MG物种的70种相关反应的实验室研究的金属化学研究。然后，该模型将用于模拟彗星飞行。第二个项目将检查这些行星大气中高覆云的现象。他们的陆地对应物（称为夜光云）是H2O冰云，夏季在高纬度地区发生了83公里。在火星上，已经观察到70至100 km之间的云，相比之下，大多数发生在赤道纬度。此外，它们是二氧化碳冰云。一个主要的挑战是解释如何形成这些云，因为温度几乎不足以使CO2在金属硅酸盐颗粒上凝结。但是，申请人最近提出的有前途的候选人是，流星的金属变成了金属碳酸盐，它们吸收了H2O形成“脏冰”颗粒，这些是二氧化碳冰的有效种子。现在将在实验室中进行测试。在金星的情况下，我们有第一个暂定报告的云层定期出现在85-90 km左右，即远高于厚厚的硫酸云，这些云层包裹着整个星球，大约在70 km左右。在这个项目中，我们将通过实验测试我们的假设，即这些分离的云由吸收H2O并变得足够稀释以冻结的硫酸引起的。较高的仍然约为120公里，温度降低了足够远，以使二氧化碳冰云与火星相同的方式形成。因此，我们将使用Venus Express航天器搜索这些云的可能可见性，而我们的项目合作伙伴则搜索云。