Comets are often known as dirtysnowballs, and consist mainly of ice and rock.
彗星一般被认为是一些脏雪球，主要由冰和岩石构成。
2
These "dirtysnowballs" castoff gas and dust whenever they venture near the sun.
这些“脏雪球”在冒险接近太阳时会丢出气体和尘埃。
3
They are now seen as "icy dirtballs", dominated by rock, in contrast to the "dirtysnowballs" hypothesised by Fred Whipple, an astronomer at Harvard University, in 1950.