Research press release


Nature Astronomy

Interstellar object ‘Oumuamua protected from the Sun by organic coat



Alan Fitzsimmonsらは、その組成を決定するために可視光と近赤外波長(0.3-1.8マイクロメートル)における天体の全体スペクトルを得た。天体表面に構造の差異が存在し、その表面は炭素を多く含んだ氷に覆われた小さな太陽系天体と似ていることが明らかにされ、その構造は宇宙線によって変えられている。彼らはオウムアムアの熱特性のモデルを構築し、天体が太陽に加熱されたとき、有機物の豊富な物質の厚さ0.5メートルのマントルが水氷に富んだ彗星に似た内部構造を蒸発から保護している可能性を明らかにした。


Long-term exposure to cosmic rays has created an insulating organic-rich layer on the surface of the interstellar visitor ‘Oumuamua, reports a paper published this week in Nature Astronomy. This coating could have protected an ice-rich interior from being vaporized during its recent passage close to the Sun.

‘Oumuamua is the first unambiguously detected interstellar body to visit our Solar System. Planetary scientists have long expected that the interstellar object population is dominated by ice-rich small bodies like comets; however, ‘Oumuamua didn’t exhibit any comet-like activity when it passed close to the Sun at the beginning of September 2017.

Alan Fitzsimmons and colleagues obtained a full spectrum of the object in the visible and near-infrared wavelengths (0.3-1.8 μm) in order to determine its composition. They find that there are compositional differences across its surface, and that the surface is similar to small Solar System bodies that are covered in carbon-rich ices, whose structure is modified by exposure to cosmic rays. They developed a model of the thermal properties of ‘Oumuamua and determine that a half-metre thick mantle of organic-rich material could have protected a water-ice-rich comet-like interior from vaporizing when the object was heated by the Sun.

These observations allow a better characterization of the structure and the history of this unique object, while also shedding light on the population of interstellar objects floating around our Solar System.

doi: 10.1038/s41550-017-0361-4

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