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Grades 3–5 · Earth & Space

Why does a comet grow tails near the Sun?

A comet’s small solid center contains ice mixed with dust and other material. Far from the Sun, it may have little visible activity. Closer in, sunlight warms the surface and some ice changes into gas.

Z009 visual explanationSolar influence shapes escaping comet material; example motion; ion tail; dust tail; Sun; Tails are material flows; they need not point backward along the orbit.Solar influence shapes escaping comet materialexample motionion taildust tailSunTails are material flows; they need not point backward along the orbit.

In the diagramSolar influence shapes escaping comet materialexample motionion taildust tailSunTails are material flows; they need not point backward along the orbit.

A small nucleus and coma feed a curved dust tail and a straighter ion tail extending broadly away from the Sun. Tail size, spacing and curvature are exaggerated.

Escaping gas can carry dust away, forming a cloud around the center called a coma. Some of this material spreads into tails. The solid center has not stretched into a long object.

Sunlight pushes on dust grains, helping form a broad, often curved dust tail. Electrically charged gas interacts with the solar wind and its magnetic field, forming a more direct ion tail away from the Sun.

The tails therefore respond to the Sun’s influence as well as to the comet’s movement. A comet can travel away from the Sun while its tail still extends away from the Sun. The tails are a changing flow of material, not a permanent part attached like a handle.

About this explanation

Starting knowledge: Know that a comet contains ice and dust, and that sunlight can supply energy.

Sources

  • NASA — Comet Facts
  • NASA Space Place — What Is a Comet?
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