【英语时差8,16】女灶神(下)（在线收听）

Vesta is quite far away. Like many asteroids, it has an orbit out between the orbits of Mars and Jupiter. Astronomers first spotted it when looking for a new planet they thought should exist between these two. As I said, Vesta is quite small–about three hundred and twenty-five miles across. So if it’s small and far away, how come we can see it from here? Vesta’s surface has a coating of pyroxine and olivine, two minerals that are actually also spewed up by volcanoes here on earth. They give it a whitish exterior that reflects well, making it just possible to see Vesta with your eyes, even when the only two larger asteroids, Ceres and Pallas, are completely invisible.