论文标题
火星磁场的基本物理和资源要求
Fundamental Physical and Resource Requirements for a Martian Magnetic Shield
论文作者
论文摘要
火星缺乏大量的磁场。结果，太阳风消融了火星气氛，使表面无法居住。因此，任何地形尝试都需要人造的火星磁性屏蔽。建立人工磁层的基本挑战是将行星尺度的电流和磁场凝结到可能的最小质量。超导电磁体提供了一种方法。但是，超导体和电磁体的潜在物理限制了这种浓度。基于这些基本限制，我们表明，超导材料的量与$ b_c^{ - 2} a^{ - 3} $成正比，其中$ b_c $是超导体的关键磁场，$ a $ a $是螺线固醇的循环半径。由于$ b_c $是由基本物理学设置的，因此设计的唯一真正可调节的参数是循环半径；较大的循环半径可最大程度地减少所需的超导材料的量。这种不直觉的结果意味着，建立紧凑的电磁体并将其放在火星和太阳之间的“直觉”策略是不可行的。考虑到$ b_c $的合理限制，最小的循环半径为$ \ sim $ 10 km，磁性屏蔽的质量为$ \ sim 10^{19} $ g。大多数高温超导体都是由罕见元素构成的。给定太阳系丰度，用$ \ sim 10^{19} $ G构建超导体将需要挖掘一个太阳系主体，几次$ 10^{25} $ g;这大约是火星的10％。我们发现，最可行的设计是用$ \ sim $ 3400 km的环形半径用超导线环绕火星。由此产生的电线直径可以小至$ \ sim $ 5厘米。通过这种设计，磁性屏蔽的质量为$ \ sim 10^{12} $ g，并且需要采矿$ \ sim 10^{18} $ g，或者只有0.1 \％的Olympus Mons。
Mars lacks a substantial magnetic field; as a result, the solar wind ablates the Martian atmosphere, making the surface uninhabitable. Therefore, any terraforming attempt will require an artificial Martian magnetic shield. The fundamental challenge of building an artificial magnetosphere is to condense planetary-scale currents and magnetic fields down to the smallest mass possible. Superconducting electromagnets offer a way to do this. However, the underlying physics of superconductors and electromagnets limits this concentration. Based upon these fundamental limitations, we show that the amount of superconducting material is proportional to $B_c^{-2}a^{-3}$, where $B_c$ is the critical magnetic field for the superconductor and $a$ is the loop radius of a solenoid. Since $B_c$ is set by fundamental physics, the only truly adjustable parameter for the design is the loop radius; a larger loop radius minimizes the amount of superconducting material required. This non-intuitive result means that the "intuitive" strategy of building a compact electromagnet and placing it between Mars and the Sun at the first Lagrange point is unfeasible. Considering reasonable limits on $B_c$, the smallest possible loop radius is $\sim$10 km, and the magnetic shield would have a mass of $\sim 10^{19}$ g. Most high-temperature superconductors are constructed of rare elements; given solar system abundances, building a superconductor with $\sim 10^{19}$ g would require mining a solar system body with several times $10^{25}$ g; this is approximately 10% of Mars. We find that the most feasible design is to encircle Mars with a superconducting wire with a loop radius of $\sim$ 3400 km. The resulting wire diameter can be as small as $\sim$5 cm. With this design, the magnetic shield would have a mass of $\sim 10^{12}$ g and would require mining $\sim 10^{18}$ g, or only 0.1\% of Olympus Mons.
