What Are The Differences Between Comets And Asteroids?

A 3D rendering of the asteroid belt.
A 3D rendering of the asteroid belt.

People have looked up at the night sky for centuries and wondered about what they see and even what lies beyond. Over time, and with the development of the study of space and astronomy, scientists have slowly begun to answer these questions, providing names for different objects in space and even predicting certain astronomical events. For those unfamiliar with the study of astronomy, these names can be confusing and hard to remember. The perfect example of this can be found with comets and asteroids, two commonly confused objects found in space. This article takes a closer look at the differences between comets and asteroids.

What Are Comets Made Of?

Comets are somewhat rounded, astronomical objects that follow a path around the sun. These objects are made up of ice, ammonia, carbon dioxide, carbon monoxide, methane, rock, dust, and other organic compounds. Because of this composition, comets are often referred to as “dirty snowballs”. The materials that form comets originated with the formation of the solar system, which took place around 4.5 billion years ago.

The Structure Of A Comet

The structure of a comet is based around the nucleus, which is the frozen center. This nucleus is surrounded by a coma, which is a large cloud of gas, water, and dust. The coma is formed when the comet passes close to the sun. The heat from the sun causes the ice in the comet to melt and vaporize, this vapor is then pulled away from the nucleus by solar wind and radiation pressure. The resulting effect is often referred to as a comet tail, which tends to point away from the sun. This process means that each time a comet comes closer to the sun, it becomes smaller as it loses material.

Types Of Comets

Comets are generally believed to fall into one of two categories: short-period and long-period.

Short-period comets, also known as periodic comets, typically take less than 200 years to complete a full orbit. These comets generally follow the same path as other planets and solar system bodies, traveling as far away as the planets of Jupiter and Neptune. As short-period comets travel close to these larger planets, they are exposed to additional gravitational pull.

Long-period comets complete a full orbit somewhere between 200 and 1,000 years. Not only do these solar system bodies take longer to make a complete orbit, but they also take an elliptical rather than circular path. The gravitational pull from larger planets may cause long-period comets to be forced outside of the solar system entirely.

What Are Asteroids Made Of?

An asteroid is an irregularly-shaped object that orbits around the sun. These solar system bodies are often considered minor planets, particularly when located in the inner areas of the solar system. Asteroids are made up primarily of minerals and rocks. Scientists believe that asteroids consist of the remains of materials that never grew large enough to be considered a planet.

The Structure Of An Asteroid

Most asteroids are very similar in structure in that they have a solid body that is marked by small craters along the surface. These objects may measure anywhere from as small as 3.28 feet in diameter to as large as 3,280,840 feet in diameter. The larger the asteroid, the more round it is in shape. As asteroids move around the solar system, they follow an orbital path while simultaneously rotating in place.

Types Of Asteroids

Asteroids are typically classified by their orbital path and by their spectral reflection.

In terms of orbital classification, an asteroid may be part of a group or family of asteroids. Asteroid groups are made up a large number of asteroids, which orbit together with a relatively loose fit. Asteroid families, on the other hand, can be found in close proximity and are believed to have originated by the separation of a larger asteroid at some point in the past.

Asteroid spectral classification is based on the color, shape, and reflective properties of these solar system bodies. Asteroids were originally separated into three spectral categories: dark, stony, and neither. Over the years, these categories have expanded as new types of asteroids have been discovered.

What Are The Differences Between Comets And Asteroids?

Researchers have identified many differences between comets and asteroids, primarily in their composition. As previously mentioned, comets consist of ice, rock, dust, and other organic compounds, while asteroids are made up of only rocks and minerals. Because of this composition, these two astronomical bodies also react differently to the sun and its heat. Comets become smaller with time, as the ice within begins to melt. Asteroids, however, maintain their size and do not lose material as they pass by the sun.

Another of the differences between comets and asteroids is in their proximity to the sun. Generally speaking, comets can be found further from the sun than asteroids, which explains the difference in composition. This distance from the sun has allowed comets to form and maintain ice. Most comets are located in either the Kuiper Belt or the Oort Cloud. The Kuiper Belt is located just beyond the orbit of Pluto, at the furthest reaches of the solar system. The Oort Cloud is an area that contains countless comets, which all orbit the sun at distances of up to 13 trillion miles. In contrast, most asteroids orbit within the asteroid belt, which is located between the planets of Mars and Jupiter.

In addition to the differences in composition and distance from the sun, comets and asteroids are also different in appearance. As previously mentioned, comets have a tail-like formation that points away from the sun. Asteroids are different and do not have this feature, nor anything similar. This tail, known as the coma, is a result of the difference in composition as it is the melting ice and vaporized gases that create the coma. Some asteroids, however, have been recorded with this tail feature. Specifically, the asteroid P2010 A2 and the asteroid 3200 Phaethon.

Comets and asteroids also tend to have a different orbital shape. Comets, for example, travel along more elongated paths around the sun. Asteroids tend to follow a more circular orbit and travel in groups when passing through belts.


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