Kaib Nathan A, Pike Rosemary, Lawler Samantha, Kovalik Maya, Brown Christopher, Alexandersen Mike, Bannister Michele T, Gladman Brett J, Petit Jean-Marc
HL Dodge Department of Physics & Astronomy, University of Oklahoma, Norman, OK 73019, USA.
Institute of Astronomy and Astrophysics, Academia Sinica; 11F of AS/NTU Astronomy-Mathematics Building, No. 1 Roosevelt Rd., Sec. 4, Taipei 10617, Taiwan.
Astron J. 2019 Jul;158(1). doi: 10.3847/1538-3881/ab2383. Epub 2019 Jul 2.
Most known trans-Neptunian objects (TNOs) gravitationally scattering off the giant planets have orbital inclinations consistent with an origin from the classical Kuiper belt, but a small fraction of these "scattering TNOs" have inclinations that are far too large ( 45°) for this origin. These scattering outliers have previously been proposed to be interlopers from the Oort cloud or evidence of an undiscovered planet. Here we test these hypotheses using N-body simulations and the 69 centaurs and scattering TNOs detected in the Outer Solar Systems Origins Survey and its predecessors. We confirm that observed scattering objects cannot solely originate from the classical Kuiper belt, and we show that both the Oort cloud and a distant planet generate observable highly inclined scatterers. Although the number of highly inclined scatterers from the Oort Cloud is ~3 times less than observed, Oort cloud enrichment from the Sun's galactic migration or birth cluster could resolve this. Meanwhile, a distant, low-eccentricity 5 M planet replicates the observed fraction of highly inclined scatterers, but the overall inclination distribution is more excited than observed. Furthermore, the distant planet generates a longitudinal asymmetry among detached TNOs that is less extreme than often presumed, and its direction reverses across the perihelion range spanned by known TNOs. More complete models that explore the dynamical origins of the planet are necessary to further study these features. With observational biases well-characterized, our work shows that the orbital distribution of detected scattering bodies is a powerful constraint on the unobserved distant solar system.
大多数已知的海王星外天体（TNOs）在与巨行星发生引力散射后，其轨道倾角与源自经典柯伊伯带的情况相符，但这些“散射TNOs”中有一小部分的倾角对于这种起源来说过大（超过45°）。此前有人提出，这些散射异常天体要么是来自奥尔特云的闯入者，要么是存在未被发现行星的证据。在此，我们使用N体模拟以及在“外太阳系起源调查”及其前身中探测到的69颗半人马小行星和散射TNOs来检验这些假设。我们证实，观测到的散射天体并非仅起源于经典柯伊伯带，并且我们表明奥尔特云和一颗遥远的行星都会产生可观测到的高倾角散射体。尽管来自奥尔特云的高倾角散射体数量比观测到的少约3倍，但太阳的星系迁移或诞生星团对奥尔特云的富集作用可能会解决这一问题。与此同时，一颗遥远的、低偏心率的5M行星能够重现观测到的高倾角散射体比例，但总体倾角分布比观测到的更为活跃。此外，这颗遥远的行星在离散TNOs中产生的纵向不对称性比通常认为的要小，并且其方向在已知TNOs跨越的近日点范围内会发生反转。需要更完整的模型来探索这颗行星的动力学起源，以便进一步研究这些特征。由于观测偏差已得到充分表征，我们的工作表明，探测到的散射天体的轨道分布对未被观测到的遥远太阳系是一个有力的约束。
