Why comets have two tails

A comet's appearance changes as it approaches the Sun. Solar heat warms the comet, giving it the following anatomy:. As a comet accelerates towards the Sun, its surface temperature increases, and ices begin to sublimate into gaseous form. By the time the comet comes within about 5 AU of the Sun, sublimation has formed a noticeable atmosphere that easily escapes the comet's weak gravity.

The coma forms as the escaping atmosphere drags away dust particles that have been mixed with the sublimating ice. More ice turns into gas as the comet approaches the Sun. Comet tails are expansions of the coma.

Comet tails point away from the Sun, regardless of the direction in which the comet is traveling. Comets have two tails because escaping gas and dust are influenced by the Sun in slightly different ways, and the tails point in slightly different directions.

Gases escaping from the comet are ionized by the ultraviolet photons from the Sun. Once they are ionized, the solar wind carries them straight outward away from the Sun. These gases form the plasma tail. This picture of the comet Hale-Bopp was photographed over Boulder, Colorado during its appearance in Dust-size particles that escape from the comet experience a much weaker push from the Sun caused by the pressure of sunlight itself called radiation pressure , rather than by the charged particles of the solar wind.

While the dust tail also points generally away from the Sun, it has a slight curve back in the direction the comet came from. The dust tail, on the other hand, diffuses wildly, largely due to the grains being various sizes and moving at a variety of speeds.

Why would the ion tail be perfectly straight while the dust tail is curved? Even if all the dust grains were somehow the same exact size and mass as one another, the forces acting on the dust tail would still cause it to show a curve. Yet, somehow, the ion tail never curves: a phenomenon noted by Brahe more than years ago.

The ion tail is faint, but still present. The reason the ion tail is straight, in this instance, is precisely because these are charged particles. The Sun itself might be incredibly massive, but it also has electromagnetic properties that can — particularly for charged particles — dominate over its gravitational effects.

Instead, it has a large, extended atmosphere that reaches all throughout the Solar System, populated by solar wind particles, coronal streamers, and a large-scale magnetic field. The comet's ionized particles, in motion, form a plasma that creates a magnetosphere around the comet, which itself interacts with the solar wind: charged particles being emitted by the Sun.

A combination of both cometary and solar ions following these magnetic field lines are responsible for the features seen in the blue ion tail: a spectacular case of agreement between simulations and observations. This animation portrays a comet as it approaches the inner solar system. As the comet nears the Sun, This creates the blue, straight ion tail; the dust tail only arrives later.

Once the Sun dips far enough below the horizon for the sky to darken sufficiently, more skywatchers than ever should be able to see it. The dust tail is made of tiny fragments of the comet itself, coming in a wide variety of grain sizes and masses, while the ion tail is only made of extremely low-mass particles, tracing out the combined magnetic field created by the Sun and comet together.

This is a BETA experience. You may opt-out by clicking here. More From Forbes. Nov 11, , am EST. Nov 10, , pm EST. Nov 9, , pm EST. Comets develop tails as they approach perihelion—the place in their orbits when they are closest to the Sun. Ultraviolet light ionizes the neutral gas blown off the comet, and the solar wind carries these ions straight out from the Sun to form the ion tail, which typically glows blue.

The dust tail on the other hand is neutral, composed of small dust particles similar in size to those found in cigarette smoke. Comets aren't the only objects in the solar system with tails — recent observations show that even asteroids can sprout dust tails on occasion.

I've been watching the Electric Universe on youtube, the claim the comets have tails because of electrical differences as it comes from way out there to the inner solar system. To be honest, it sounds just a little more believeable than a dirty snowballs melting away as it gets closer to our sun. Can you comment on this? Again to be honest, after billions of years, the dirty snowball theory shouldn't hold up, even 1 trip around the sun.

Log in to Reply. Why would there be a tail of a comet if there is nothing forcing the gases or debris to slow down more than the comet? Why would not the debris continue at the same speed, with the comet?