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📘 How does a comet grow a tail?

Far from the Sun, a comet is a cold nucleus of rock dust mixed with frozen water, carbon dioxide, and other volatiles. It usually has no visible tail until sunlight delivers enough energy to change the surface.

5
lessons
~25 min
to learn
Adults
level
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What you’ll learn

  1. A frozen nucleus wakes upExplain how sunlight activates a cold, icy nucleus through sublimation and jets.A warming nucleus releases finite volatile material as gas and dust.
  2. The coma becomes a headDistinguish the nucleus, coma, and chemistry of released comet material.Gas and dust expand into a bright coma around the tiny nucleus.
  3. Two tails, two forcesCompare the dust tail driven by radiation pressure with the ion tail shaped by the solar wind.Different particles feel different forces, producing two different tail shapes.
  4. Why the tail points awayUse solar-wind flow and magnetic fields to explain the anti-sunward ion tail.Charged gas is carried outward by the Sun's magnetized plasma flow.
  5. Read a comet's tailSynthesize sublimation, particle forces, observations, and fading activity into one explanation.A tail is a temporary, measurable record of a comet interacting with sunlight and space weather.

Questions this course answers

What process changes comet ice directly from solid to gas?

Sublimation is the solid-to-gas phase change that releases volatile material from the warming nucleus.

Put the first stages of comet activity in order.

Heating starts the chain, and the tail forms after material has escaped into the coma.

What is the coma?

The coma is the expanding atmosphere produced around the nucleus by sublimation and sunlight-driven chemistry.

Match each part with its main description.

Each term names a different stage or material in the comet's visible structure.

What mainly pushes fine dust into a comet's broad tail?

Photons transfer momentum to dust, partly countering solar gravity and spreading grains into curved paths.

Why can the ion tail be straighter than the dust tail?

The solar wind and its magnetic field accelerate and guide the charged gas more strongly than sunlight guides dust.

Grounded in trusted sources

  • NASA Science, Comet Facts, https://science.nasa.gov/solar-system/comets/facts/
  • NASA Science, Chapter 1: The Solar System, https://science.nasa.gov/learn/basics-of-space-flight/chapter1-3/
  • NASA Space Place, What Is a Comet?, https://spaceplace.nasa.gov/comets/en/
  • NASA, Comet Encke: A Solar Windsock Observed by NASA's STEREO, https://www.nasa.gov/science-research/heliophysics/comet-encke-a-solar-windsock-observed-by-nasas-stereo/
  • NASA SVS, Comet vs. Sun, https://svs.gsfc.nasa.gov/11732/
  • NASA GSFC, The Solar Wind, https://pwg.gsfc.nasa.gov/Education/wsolwind.html
  • Wikimedia Commons MediaWiki API, https://commons.wikimedia.org/w/api.php

Every Wunder lesson is built from real, reputable sources — never invented.

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