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arXiv 1607.08591astro-ph.EP
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均匀三轴粘弹性体的潮汐自旋下降速率

Tidal spin down rates of homogeneous triaxial viscoelastic bodies

Alice C. Quillen, Andrea Kueter-Young, Julien Frouard, Darin Ragozzine

摘要:

我们使用数值模拟来测量一个均匀的三轴椭球体的潮汐自旋下降率的敏感性,其轴比通过比较在轨道半长轴上的漂移率,具有相同的质量,体积和模拟流变学的球体。我们使用一个质量弹簧模型近似的粘弹性体旋转其最短的身体轴,自旋与轨道自旋轴对齐,并在圆形轨道上的质点。如果乘以$0.5 (1 + b^4/a^4)(b/a)^{-4/3} (c/a)^{-α_c}$,则可以根据具有等效体积的球体的预测值来估计扭矩或漂移速率,其中$b/a$和$c/a$是体轴比,并且指数$α_c \approx 1.05$与随机晶格质量弹簧模型模拟一致,但$α_c = 4/3$由缩放估计建议。轴比为0.5和0.8的均匀天体,如妊神星,其轨道半长轴漂移速率大约是具有相同质量、体积和材料性质的球体的两倍。模拟一个主要由岩石组成的天体,但其20%的质量是集中在其两端的冰,其漂移速度比同等的均匀岩石球体快10倍。然而,这种漂移率的增加不足以让妊神星的卫星Hi'iaka潮汐地从妊神星漂移到它现在的轨道半长轴。

英文摘要:

We use numerical simulations to measure the sensitivity of the tidal spin down rate of a homogeneous triaxial ellipsoid to its axis ratios by comparing the drift rate in orbital semi-major axis to that of a spherical body with the same mass, volume and simulated rheology. We use a mass-spring model approximating a viscoelastic body spinning around its shortest body axis, with spin aligned with orbital spin axis, and in circular orbit about a point mass. The torque or drift rate can be estimated from that predicted for a sphere with equivalent volume if multiplied by $0.5 (1 + b^4/a^4)(b/a)^{-4/3} (c/a)^{-α_c}$ where $b/a$ and $c/a$ are the body axis ratios and index $α_c \approx 1.05$ is consistent with the random lattice mass spring model simulations but $α_c = 4/3$ suggested by scaling estimates. A homogeneous body with axis ratios 0.5 and and 0.8, like Haumea, has orbital semi-major axis drift rate about twice as fast as a spherical body with the same mass, volume and material properties. A simulation approximating a mostly rocky body but with 20\% of its mass as ice concentrated at its ends has a drift rate 10 times faster than the equivalent homogeneous rocky sphere. However, this increase in drift rate is not enough to allow Haumea's satellite, Hi'iaka, to have tidally drifted away from Haumea to its current orbital semi-major axis.

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