Research press release


Nature Geoscience

Wobbly past of Ceres revealed



Pasquale Tricaricoは今回、ドーンが取得したケレスの重力と形状のデータを解析し、向きの変化を引き起こす可能性がある密度の高い地殻が、現在の赤道付近に存在することを見いだした。また、準惑星を一周する古代の嶺の証拠が、現在の赤道から36度傾いた位置に見いだされた。この嶺は、ケレスの元々の赤道を表している可能性があり、地殻が比較的厚いため、向きが変わる間に外側に膨らんだと考えられる。また、地殻表面に見られる大きな割れ目の分布も、向きの変化事象の仮説と合致しており、ケレスや、おそらく他の同じようなサイズの氷天体における内部の複雑な歴史が示唆される。

The dwarf planet Ceres reoriented itself early in its history due to changes in the density of its crust, suggests a study published online this week in Nature Geoscience. Such a reorientation may explain some fractures and a planet-circling ridge seen on Ceres’ surface.

Some planets and moons in our solar system are thought to have reoriented, shifting the location of their poles in response to changes in the distribution of their masses. Reorientations can result from processes such as mountain building. Mars, for example, is thought to have shifted as to move the massive Tharsis volcanic region to a more stable position nearer the equator. Plate tectonics, which can also drive reorientations, is believed to have gradually reoriented Earth in the past. Orbiting Ceres, NASA’s Dawn spacecraft has found evidence that the dwarf planet has a variably ice-rich crust, which could indicate large differences in density across the body.

Pasquale Tricarico analyses gravity and shape data taken by Dawn, finding an area of dense crust near Ceres’ present equator that might have driven a reorientation. He also finds evidence of an ancient ridge circling the dwarf planet at an angle of 36° from the present equator. This ridge may represent Ceres’ original equator, which could have bulged outwards during reorientation because of its relatively thick crust. The distribution of the large fractures seen on the surface of the crust is also consistent with the proposed reorientation event - suggesting a complex interior history for Ceres, and perhaps other similarly sized icy bodies.

doi: 10.1038/s41561-018-0232-3


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