The Martian Radiation Environment - Early Mars and Future Measurements with the Radiation Assessment Detector
The Martian Radiation Environment - Early Mars and Future Measurements with the Radiation Assessment Detector
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火星辐射环境 - 早期火星和未来使用辐射评估探测器的测量
DOI：
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发表时间：
2012
期刊：
影响因子：
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通讯作者：
B. Ehresmann
中科院分区：
文献类型：
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作者：
B. Ehresmann
今天，火星表面是一个不适合任何形式生命的环境。由于其稀薄的大气层和缺乏全球磁场，火星只受到来自外太空的带电粒子的微弱保护。特别是，高能银河宇宙射线可以通过大气层一直传播到地面。这些高能粒子与大气和土壤中产生的次级粒子一起，沿着形成了可能对生命构成危险的表面辐射环境。为了估计这一风险，辐射评估探测器（RAD）将测量表面的辐射暴露，作为2011年11月发射并计划于2012年8月抵达火星的火星科学实验室探测器使命的一部分。
此外，有大量证据表明，在火星历史的早期，火星上的条件更适合生命的出现。特别是诺亚时期（约40亿年前）被认为是一个有希望的时间跨度。大气层相当稠密，并受到全球磁场的屏蔽，在表面可以发现大量的液态水。这些因素表明，辐射环境对生命的危险较小。因此，量化早期火星上的辐射暴露对于生命是否可能在那里出现的问题非常重要。
在这篇论文中，较高的大气压力，对应于一个密集的诺亚大气，对辐射照射的表面和下面的影响进行了分析。此外，较大体积的液态表面水和地下水冰的存在下的辐射场的影响进行了测定。为此，开发了一个模型，通过Monte Carlo方法从这些条件下的计算粒子通量计算辐射剂量率。在这项工作的范围内，现有的参数空间的火星辐射研究的扩展，计算剂量率的广泛的粒子种类的广泛的环境变化。
作为本文的第二个主要部分，建立了一个反映RAD机载数据处理和简化的模型。详细解释了电子处理逻辑的设置，并描述了该仪器如何区分穿透探测器并停在其中的粒子中的被测带电粒子。该模型用于确定区分粒子所需的切割值。此外，它表明，该模型是能够正确区分穿透和停止带电粒子在测量的校准数据。此外，本研究的发现被用来改善加工逻辑。
Today, the surface of Mars is an inhospitable environment for any form of life. Due to its thin atmosphere and lack of a global magnetic field, Mars is only weakly protected from charged particles impeding the planet from outer space. In particular, high-energetic galactic cosmic rays can propagate all the way through the atmosphere to the ground. These high-energetic particles create, along with secondary particles produced in the atmosphere and the soil, a surface radiation environment that can pose a possible hazard for life. To estimate this risk, the Radiation Assessment Detector (RAD) will measure the radiation exposure on the surface, as part of the Mars Science Laboratory rover mission, launched in November 2011 and slated to arrive at Mars in August 2012.
Furthermore, there is substantial evidence that, early in the planet's history, conditions on Mars were much more suited for an emergence of life. Especially the Noachian period (~ 4 billion years ago) is deemed as a promising time span. The atmosphere was considerably denser and shielded by a global magnetic field, and large amounts of liquid water could be found on the surface. These factors indicate a radiation environment less dangerous for life. Thus, quantifying the radiation exposure on early Mars is of high importance for the question if life could have ever emerged there.
In this thesis, the influence of higher atmospheric pressure, corresponding to a denser Noachian atmosphere, on the radiation exposure on and beneath the surface is analysed. Furthermore, the influence of the presence of larger volumes of liquid surface water and subsurface water ice on the radiation field are determined. For this, a model was developed that calculates radiation dose rates from computed particle fluxes for these conditions via Monte Carlo methods. In the scope of this work, the existing parameter space of Martian radiation research is expanded by calculating dose rates of a wide set of particle species for a broad range of environmental changes.
As a second main part of this thesis, a model that mirrors an important part of RAD's onboard data processing and reduction was developed. The setup of the electronics' processing logic is explained in detail and it is described how the instrument aims to distinguish measured charged particles onboard in particles penetrating the detector and stopping in it. The model is used to determine necessary cut values for the particle distinction. Additionally, it is shown that the model is able to correctly distinguish penetrating and stopping charged particles in measured calibration data. Furthermore, findings from this research are employed to improve the processing logic.