The International Astronomical Union reports that there are now 79 known Jovian moons, with a dozen found last year.

国际天文学联合会报告称，加上去年发现的十二个，木星现在有79个卫星。

撰文播音：史蒂夫·米尔斯基（Steve Mirsky）

翻译：张朵儿

审校：张艺箫

How many moons does Jupiter have? If you said four, you might be Galileo. If you said 69, you were right. Until the announcement this morning by the International Astronomical Union of the discovery of an additional 10 moons about the gas-giant planet. Bringing the currently known total to 79. That’s a lot of moons.

木星有多少颗卫星？如果你回答4个，那你可能是伽利略。如果你回答69个，今天早上之前，你是对的。但就在今天早上，国际天文联合会发布声明，确定增加十个木星卫星，总数将达到79。这个数量很大。

A research team from the Carnegie Institution for Science, the University of Hawaii and Northern Arizona University was looking in 2017 for very distant objects in our solar system, well beyond Pluto. Jupiter happened to be in the same field of view, so they also looked for any as yet unknown moons. They found 12, two of which were announced last year. Confirmation of the moons required multiple observations, and those data enabled a calculation of the moons’ orbits.

2017年间，一个由卡内基科学研究所、夏威夷大学和北亚利桑纳大学的研究小组致力于在太阳系中寻找比冥王星更遥远的天体。木星正好处在观测的同一块视野内，所以科研小组同时也在寻找木星未被发现的卫星。他们一共找到了12个，其中有2个已经在去年发布。确认一颗卫星需要大量的观测数据，并通过这些数据计算卫星的轨道。

Nine of the dozen moons are well away from Jupiter and have retrograde orbits, meaning they go around the planet in what we’d think of as the “wrong direction.” They take about two Earth years to complete their circuits.

这些卫星中的9颗距离木星非常的远，并且轨道逆行（卫星绕行方向有同向性，一般与行星自转方向相同）。这些卫星绕行的周期是两个地球年左右。

Two new moons are closer in, go the right way, and take about an Earth year for one orbit. Those eleven moons are probably remnants of larger bodies that got broken up in collisions.

有2颗卫星相比之下距离木星比较近，且顺行，绕行周期为一个地球年。这11颗卫星有可能是一个大星体在发生碰撞之后的产物。

The remaining moon is less than a kilometer across, further out than the two conventional moons and has a 1.5-year orbit—and the orbit is inclined. That tilt has the weird little moon crossing the paths of those outer retrograde moons. Which means an increased likelihood of a big smash-up one day.

还有一个卫星直径不到一公里，比那两个正常的卫星离木星更远一点，轨道周期为1.5地球年并且轨道是倾斜的。这颗诡异的小卫星和逆行卫星的轨迹有交叉，极有可能在未来的某一天发生碰撞。

Depending on what survives from any such collision, Jupiter may then have even more moons. Or a couple fewer.

由于碰撞之后剩余星体情况不同，木星的卫星数量可能还会增加，也有可能会减少。