十万个为什么·科学启蒙30篇（3）

1 / 30

彗星为什么会有尾巴

Comets are icy bodies that orbit the Sun in long, stretched-out paths.
When a comet approaches the Sun, its surface warms up and releases gas and dust.
Solar radiation and the solar wind push this material away from the nucleus.
The glowing gas forms an ion tail, which always points directly away from the Sun.
The dust tail curves slightly because tiny particles respond to both sunlight and gravity.
These tails can stretch millions of kilometers but remain extremely thin and faint.
A comet only develops visible tails when it is inside the orbit of Mars.
Once it moves farther out again, the ice freezes solid and the tails vanish.
This process repeats every time the comet returns on its orbital journey.
So the tail isn’t left behind—it’s freshly made each time the comet gets warm.