A comet’s two tails start in its sun-warmed atmosphere
As a comet approaches the Sun, heat releases gas and dust from its icy surface. The escaping material forms a hazy cloud around the solid nucleus called the coma. From that cloud, sunlight and the solar wind sort the material into two distinct streams.
Dust takes the scenic route
Sunlight exerts a small outward push on dust grains, called radiation pressure. But those grains also keep moving along the comet’s orbit—the curved path it is traveling through space. Because grains are released at different times and sizes, their motions spread into a broad, often curved tail. It can appear to trail behind the comet, but it is not simply a plume dragged along its track.
Charged gas is swept straight away
Sunlight can strip electrons from some gas molecules in the coma, turning them into electrically charged particles called ions. The solar wind—a flow of charged particles streaming from the Sun—carries magnetic fields through space. Those fields steer the ions into a relatively narrow tail pointing away from the Sun.
That tail can respond quickly when the solar wind changes, while dust grains follow their own orbital motions. So the two tails are not just different shapes: they record two different forces acting on material shed by the same comet. A change in their direction or structure can reveal what is pushing them, even when the comet itself is only a small, distant point.
