①Researchers at Cornell University say that what we know as the Moon is in fact not the only one orbiting our planet at any given time.Smaller objects regularly inhabit(存在于) the Earth's orbit，usually leaving after a few months to continue on their celestial journeys. The discovery is considered a major breakthrough for space research because scientists had been working toward visiting asteroids(小行星) outside of Earth's orbit for research.While these temporary moons are too small for a shuttle landing(航天飞机降落)，they are prime for research from a relatively close distance.