An asteroid (2010 SO16) has been discovered that has trailed the Earth in an almost identical orbit to ours for a quarter-million years. Karen Hopkin reports

When you hear about asteroids close to the Earth, you probably have visions of [--1--] and extinctions and a postapocalyptic future. Or of brave space cowboys trying to [--2--] course. You probably don’t picture a puppy that’s followed you home. But astronomers have found just that: an asteroid that’s been on Earth’s tail for at least a quarter of a million years. The observations were published by the Royal Astronomical Society.

The asteroid was first spotted during a [--3--] performed by a satellite. But it was the asteroid’s earthlike orbit that really got the astronomers’ attention. The object’s orbit is virtually the same distance from the sun as is the Earth’s. And unlike most near-Earth asteroids—whose [--4--], egg-shaped orbits take them straight through the solar system—this asteroid’s orbit’s almost circular. So it seems to be following in our footsteps, although it’s never come closer than about 50 times the distance to the moon.

Where this companion came from is anybody’s guess. It could be left over from the same material that made our planet. Which would make it less like a puppy and more like an [--5--]. One we hope will never hit us.
【视听版科学小组荣誉出品】 collisions knock them off routine survey eccentric annoying sibling当听到小行星靠近地球时,你脑海中可能会浮现小行星撞击,物种灭绝的世界末日后的场景, 或者是太空牛仔消灭它们的场景. 但你肯定不会想到一只小狗跟着你回家的画面. 但是, 天文学家发现一颗小行星尾随地球已有至少25万年历史. 该观测结果由英国皇家天文学会发布. 这颗小行星由一颗卫星执行例行监测时发现, 而正是它的类地轨道激起了天文学家们的兴趣. 该天体到太阳的轨道距离与地球到太阳的距离几乎一致. 但是, 和其他近地小行星不一样的是, 这些小行星的离心鸡蛋型轨道带着它们在太阳系中穿梭, 而这颗小行星的轨道接近圆形, 看起来似乎在追随地球的轨迹, 但是距离始终保持在月地距离的50倍以上. 所有人都在猜想这个"小东西"从何处而来. 这颗小行星有可能是地球形成后剩余的物质, 只是不太像是地球的"小跟班",到更像是一个惹人讨厌的"兄弟",希望不要来个"亲密接触"才好.