【天文学】ハウメアに環があった

The presence of a ring around Haumea, a dwarf planet located beyond Neptune, is reported online this week in Nature. This discovery opens up new avenues of research in the trans-Neptunian region.

Of the four known dwarf planets in the Solar System that orbit the Sun at a greater average distance than does Neptune, Haumea is an unusual, very elongated and fast-rotating body. In contrast to the other dwarf planets, its size, shape, albedo (or reflectance) and density are not well understood. Although Chariklo, one of the minor planets known as Centaurs, was the first body other than a giant planet to show a ring system, Haumea is the first body outside the Centaur population that has a ring.

Jose Luis Ortiz and colleagues predicted that Haumea would cross paths with the star URAT1 533-182543 and arranged observations from 12 different telescopes at 10 different laboratories on 21 January 2017. The authors were able to determine the density (which has an upper limit of about 1,885 kilograms per cubic metre), shape (ellipsoid), albedo (0.51) and atmosphere (none) of the dwarf planet.

They also found that Haumea’s ring lies in the same plane as its equator and as the orbit of its outer moon, Hi’iaka. The ring has an orbital period that is three times the spin period of Haumea, a radius of about 2,287 kilometres and a width of 70 kilometres.