利用ALMA测量矮行星卫星的质量与密度
Masses and densities of dwarf planet satellites measured with ALMA
AI总结：
本文利用ALMA高精度天体测量测得Orcus-Vanth质量比高达0.16±0.02，并给出Eris-Dysnomia质量比上限0.0085及Dysnomia密度上限1.2 g cm⁻³，为巨撞击卫星形成机制提供了关键约束。
摘要：
我们利用阿塔卡马大型毫米/亚毫米波阵列（ALMA）对矮行星Orcus及其卫星Vanth在一个完整轨道周期内进行了精确的绝对天体测量定位，并探测到了Orcus的天体测量摆动。同时，我们还对矮行星Eris的卫星Dysnomia在其轨道上引起的天体测量摆动设定了上限。根据Vanth-Orcus质心运动，我们得到Vanth与Orcus的质量比为0.16±0.02，这是目前已知所有行星或矮行星中最高的质量比。这一较大的质量比与以下假说一致：Vanth是该系统中一次巨大碰撞后基本保持完整的撞击体，且该系统很可能已演化至双重同步状态。对于Eris，我们仅获得了其质心运动的上限，由此得到Dysnomia与Eris质量比的1σ上限为0.0085，该值接近模型预测的过渡区域——该区域区分了由巨大撞击产生、基本保留原始撞击体完整残骸的卫星与由撞击后剩余盘物质重新吸积形成的卫星。Dysnomia的低反照率使我们略微倾向于完整的撞击体情景。我们发现Dysnomia的密度小于1.2 g cm⁻³，显著低于Eris的2.4 g cm⁻³。
英文摘要：
We have used the Atacama Large Millimeter Array (ALMA) to measure precise absolute astrometric positions and detect the astrometric wobble of dwarf planet Orcus and its satellite Vanth over a complete orbit. We also place upper limits to the astrometric wobble induced by Dysnomia on dwarf planet Eris around its orbit. From the Vanth-Orcus barycentric motion, we find a Vanth-Orcus mass ratio of 0.16$\pm$0.02 -- the highest of any known planet or dwarf planet. This large ratio is consistent with the hypothesis that Vanth is a largely-intact impactor from a giant collision in the system, and that the system has likely evolved to a double synchronous state. We find only an upper limit of the barycenter motion of Eris, which implies a one sigma upper limit to the Dysnomia-Eris mass ratio of 0.0085, close to the modeled transition region between giant impact generated satellites which are largely intact remnants of the original impactor and those which form out of reaccreted disk material left over post-impact. The low albedo of Dysnomia leads us to marginally favor the intact impactor scenario. We find that Dysnomia has density of <1.2 g cm$^{-3}$, significantly lower than the 2.4 g cm$^{-3}$ of Eris.
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