Implications of Philae Magnetometry Measurements at Comet 67P/Churyumov-Gerasimenko for the Nebular Field of the Outer Solar System
Implications of Philae Magnetometry Measurements at Comet 67P/Churyumov-Gerasimenko for the Nebular Field of the Outer Solar System
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DOI：
10.3847/1538-4357/ab0f2a
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发表时间：
2019-04-10
影响因子：
4.9
通讯作者：
Auster, Hans-Ulrich
中科院分区：
文献类型：
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作者：
Biersteker, John B.;Weiss, Benjamin P.;Auster, Hans-Ulrich
太阳系天体的剩余磁化反映了它们的吸积机制、形成的空间环境以及随后的地质演化。特别是，有人提出，一些原始体可能由于它们在背景磁场中的吸积而形成了大范围的相干剩余磁化区域。Rosetta磁强计和等离子体监测器的测量表明，67P/Churyumov-Gerasimenko(67P)彗星的表面磁场小于0.9nT。为了约束67P中剩余磁化强度的空间尺度和强度，我们假设了均匀磁化强度的各种特征空间尺度，对其磁场进行了建模。我们发现，对于半径为>；=10 cm的相干磁化区，比磁矩小于或接近5×10(-6)Am(2)kg(-1)。如果67P是在太阳星云的生命周期内形成的，并且没有发生重大的随后的碰撞或水溶液变化，那么这种非常低的比磁化强度与它的形成是不一致的，它是由一团毫米大小的鹅卵石云在大于或类似于3µT的背景磁场中轻微引力坍塌而形成的。根据其他Rosetta仪器的证据，67P是由鹅卵石堆过程形成的，这表明在年轻太阳15-45Au时，星云磁场小于或类似于3µT。这一约束与原行星盘的磁驱动演化理论是一致的。
The remanent magnetization of solar system bodies reflects their accretion mechanism, the space environment in which they formed, and their subsequent geological evolution. In particular, it has been suggested that some primitive bodies may have formed large regions of coherent remanent magnetization as a consequence of their accretion in a background magnetic field. Measurements acquired by the Rosetta Magnetometer and Plasma Monitor have shown that comet 67P/Churyumov-Gerasimenko (67P) has a surface magnetic field of less than 0.9 nT. To constrain the spatial scale and intensity of remanent magnetization in 67P, we modeled its magnetic field assuming various characteristic spatial scales of uniform magnetization. We find that for regions of coherent magnetization with >= 10 cm radius, the specific magnetic moment is less than or similar to 5 x 10(-6) A m(2) kg(-1). If 67P formed during the lifetime of the solar nebula and has not undergone significant subsequent collisional or aqueous alteration, this very low specific magnetization is inconsistent with its formation from the gentle gravitational collapse of a cloud of millimeter-sized pebbles in a background magnetic field greater than or similar to 3 mu T. Given the evidence from other Rosetta instruments that 67P formed by pebble-pile processes, this would indicate that the nebular magnetic field was less than or similar to 3 mu T at 15-45 au from the young Sun. This constraint is consistent with theories of magnetically driven evolution of protoplanetary disks.