00 · IN THREE MINUTES
The answer in three steps
- 1A comet's nucleus contains volatile ices mixed with dust and rock.
- 2Solar heating releases gas and drags dust into a surrounding coma.
- 3Radiation pressure shapes a curved dust tail while the solar wind organizes a straighter ion tail.
01 · THE NUCLEUS BECOMES ACTIVE
The nucleus becomes active
Far from the Sun many cometary ices remain quiet. As the surface warms, exposed volatiles turn directly into gas and escape through diffuse regions and focused jets.
02 · GAS CARRIES DUST OUTWARD
Gas carries dust outward
Escaping molecules collide with and lift grains from the weakly bound surface. The temporary atmosphere is the coma; it can grow far larger than the solid nucleus.
The nucleus becomes active
Far from the Sun many cometary ices remain quiet. As the surface warms, exposed volatiles turn directly into gas and escape through diffuse regions and focused jets.
solar heatingGas carries dust outward
Escaping molecules collide with and lift grains from the weakly bound surface. The temporary atmosphere is the coma; it can grow far larger than the solid nucleus.
coma formationOne comet can have several tails
Dust grains respond mainly to sunlight and keep some orbital motion, producing a broad curved tail. Ionized gas couples to the solar wind and its magnetic field, producing a narrower ion tail.
force sortingAway from the Sun is not behind the comet
Both main tails point broadly anti-sunward. As the comet rounds the Sun, a tail may appear to lead its motion because orientation follows the Sun rather than the direction of travel.
anti-sunward03 · ONE COMET CAN HAVE SEVERAL TAILS
One comet can have several tails
Dust grains respond mainly to sunlight and keep some orbital motion, producing a broad curved tail. Ionized gas couples to the solar wind and its magnetic field, producing a narrower ion tail.
04 · AWAY FROM THE SUN IS NOT BEHIND THE COMET
Away from the Sun is not behind the comet
Both main tails point broadly anti-sunward. As the comet rounds the Sun, a tail may appear to lead its motion because orientation follows the Sun rather than the direction of travel.
05 · THE SURFACE IS NOT A CLEAN SNOWBALL
The surface is not a clean snowball
Rosetta found a dark, complex and evolving surface on comet 67P. Activity depends on shape, seasons, fractures, composition and illumination, so real comets do not turn on uniformly.
06 · SOURCES AND EVIDENCE
Sources and evidence
The explanation follows the evidence chain below. Links open the original source.
- 01Comets: FactsINSTITUTIONAL EXPLAINER ↗
Supports a specific claim or evidence boundary used in this article.
- 02Rosetta: CometsOFFICIAL DATA / TECHNICAL REPORT ↗
Supports a specific claim or evidence boundary used in this article.
- 03The Plasma Environment of Comet 67PPEER-REVIEWED REVIEW ↗
Supports a specific claim or evidence boundary used in this article.