关于四大行星（用英语）

A nonluminous celestial body larger than an asteroid or a comet, illuminated by light from a star, such as the sun, around which it revolves. In the solar system there are nine known planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.
行星：比一颗小行星或一颗彗星大的不发光的天体，由它绕转的恒星，如太阳的光所照亮在太阳系中有九个已知的行星：水星、金星、地球、火星、木星、土星、天王星、海王星和冥王星