KITES: CHARACTERISTICS, WHAT THEY ARE MADE OF, SHAPE AND EXAMPLES - ARTE - 2025

The comets are small irregularly shaped planets belong to the solar system, because they are linked to the Sun by the force of gravity. The term "comet" comes from the Greek and refers to the "hair" of the comet, the long trail that becomes visible when it approaches the Sun.

Comets come from the original cloud of matter that gave rise to our solar system, currently they are rather towards the outskirts of it, although sometimes their orbit brings them to the vicinity of the Earth.

Figure 1. The most popular comet of all: Halley. Source: Wikimedia Commons. NASA / W. Liller

These occasional visitors are composed of grains of non-volatile material, such as dust and rocks, along with frozen gases. Although today they are respectable members of the solar system, in ancient times their unexpected appearance heralded catastrophes and wars.

The famous English astronomer Edmond Halley (1656-1742) was the first to study comets in detail from a scientific point of view. Halley concluded that they were periodic visitors and calculated the orbit of one of them. Based on his calculations, he predicted the return of the comet for 1757, although this was delayed a bit and arrived the following year. The comet was named after him: Halley's Comet.

Comets were abundant throughout the primitive solar system, although today they are relegated to the outskirts, visiting from time to time the neighborhood of the Sun. The bad reputation that accompanied them for so long is unfair, since it is very likely that they brought the ice with them. that the atmosphere of the planets was formed, the Earth included.

In this way the foundations were established so that life could prosper. There are even those who claim that life came to Earth from other places in space, precisely through comets. This is the well-known Panspermia theory.

What are comets made of?

The material that makes up comets is the same as the rest of the solar system, which came from an immense cloud of dust and gas. This cloud in turn probably originated from a supernova explosion.

About 4.6 billion years ago the cloud, made up mostly of hydrogen and helium, was slowly spinning around a young Sun and its particles colliding with each other. The force of gravity caused many particles to clump together to become planets, but the collisions also fragmented other objects.

Many of them became asteroids and comets, or helped to form other planets. For example, the composition of Uranus and Neptune, giant outer planets, is very similar to that of comets.

Astronomical spectroscopy

The light emitted by comets reveals a lot of valuable information about their composition and structure. It is possible to carry out a spectral analysis - study of the light - of the comet when it gets close enough to the Sun. The intense heat from the star then causes the comet's material to evaporate, releasing ionized atoms and molecules.

Photons with certain characteristics - emission lines - are also emitted, which are analyzed using spectroscopy techniques. In this way, the presence of free radicals - highly reactive chemical species - can be unequivocally identified, such as CH, CN and NH2, for example.

Among the substances that are part of comets are water, organic compounds, ammonia, methane, monoxide, carbon dioxide and silicates. Regarding the elements present in them, sodium, iron and magnesium have been detected.

What shape are comets?

The size of a typical kite is, on average, about 10 km in diameter, although there are more than 50 km. It is not a very impressive size and its appearance far from the Sun is very close to that of an asteroid: a more or less amorphous and frozen body.

When the comet approaches the Sun and is exposed to radiation, its appearance changes considerably, appearing a distinctive structure.

Structure of a comet

A comet contains the following parts:

-Core

-Hair

-Tail

The hair of the comet or coma, made of dust and gas, is a halo of diffuse and shiny material that surrounds an icy center called the nucleus. The structure made up of the nucleus and the hair is the head of the comet.

They also develop tails, called caudas. There are usually two, although a spectacular comet seen in 1744 developed six tails.

One of the pipes is straight and is made up of gases, and can measure up to 10 million kilometers. It appears thanks to the action of the so-called solar wind, a shower of highly ionized particles that the Sun continuously emits from the solar corona. The magnetic field associated with this movement of the particles pushes the gas away from the hair.

The other cauda or tail is the extension of the dust of the comet's hair, as it is vaporized by the heat of the Sun. It has a curved shape that extends through space between 10 and 100 million kilometers.

Figure 2. Structure of a comet. Source: Wikimedia Commons. Kelvinsong

Some people mistake comets for meteors or shooting stars, but the former, though changeable in shape, are visible for days, weeks, and even months. The following is a Hubble image of Comet 73P / Schwassmann-Wachmann losing its tail:

Shooting stars or meteors, on the other hand, are the remnants that comets have left behind near the Sun. When the Earth encounters this debris periodically, the well-known meteor showers appear in the night sky.

Comet collisions

For a long time, it was thought that if a comet collided with Earth there would be no major problems, since these objects are mostly dust and gas.

However, it is now known that it can have catastrophic results, especially after observing the collision of Comet Shoemaker-Levy 9 with Jupiter in 1994.

The orbit of Shoemaker-Levy 9 brought it so close to Jupiter that its powerful gravity fragmented it into pieces, many of which were rapidly volatilized, but others between 1 and 2 km wide more or less, hit against the planet.

Huge fireballs and dark markings were produced in Jupiter's upper atmosphere, which lasted for quite some time.

The shock wave from a collision like that would have devastating effects on Earth. Not to mention that the atmosphere darkened for months would block the sunlight, preventing plants from carrying out photosynthesis and interrupting the food chain.

From where they come?

In its early days, the solar system was full of comets everywhere, but over time they have moved away from the inner solar system, perhaps due to the powerful gravity of the outer planets, although they do visit us from time to time.

There are usually about fifteen or twenty visible at any one time with the help of telescopes. But when it comes to comets visible to the naked eye, on average one occurs in every decade.

Astronomers believe that comets mostly come from three outer regions of the solar system:

-The Kuiper belt

-The Oort cloud

-The scattered disk

Kuiper Belt

The existence of the Kuiper belt was proposed by Kuiper and Whipple around 1950. It is an area that begins near the orbit of Neptune and continues in a radius of 10 astronomical units (ua) beyond Pluto.

An astronomical unit is equivalent to the distance that separates the Earth from the Sun, equivalent to 150 million kilometers. Measured with the Sun at its center, the Kuiper belt has a radius of between 30 and 55 ua

Many comets left the vicinity of the solar system to reach this region, due to gravitational interaction. New comets form there too.

The Kuiper belt is also home to trans-Neptunian objects, which are members of the solar system whose orbit is beyond Neptune. The diameter of these objects ranges from 100 to 1000 kilometers, so Pluto and its moon Charon are the largest trans-Neptunian objects known to date.

Possibly the trans-Neptunian objects were destined to become another great planet, however for some reason this was not the case. Perhaps it was because the material that composes it was too dispersed after the formation of Neptune and gravity was not enough to compact it.

Oort Cloud

For its part, the Oort Cloud or Opik-Oort Cloud, is a huge spherical cluster full of comets that surrounds the Sun in a radius of 1 light year or 50,000 UA. Its size is much larger than the Kuiper belt.

Some of the most striking comets come from this area of ​​space, as well as the so-called long-period comets. The period is the time it takes for the comet to travel its orbit, if it is very long, the period is longer.

Astronomers believe that perhaps the best-known comet of all, Halley's Comet, although it does not have a long period, comes from the Oort Cloud and not the Kuiper belt, as would be expected. The long-period comet Hale-Bopp also comes from there.

What happens is that the gravitational pull of the Sun decreases with distance, and then other stars and objects can alter the orbit of those in the Oort Cloud. In this way they can substantially modify their orbit and be sent to the interior of the solar system.

Figure 3. Diagram showing the inner solar system, the outer solar system, the Oort cloud, and the orbit of Sedna. Source: Wikimedia Commons. Basketteur

The scattered disk

Recently astronomers have proposed the existence of a new region in the solar system, called the scattered disk or diffuse disk. It overlaps in part with the Kuiper belt, extending perhaps for 500 ua or a little more.

The number of objects in this area is also unclear, but they are known to be rocky and icy, composed of metal and ice. The size of these objects is also on the order of 100-1000 km and some are even larger, for example the dwarf planet Eris, 2300 km in diameter, larger than Pluto.

Their orbits are very elongated and astronomers believe it is due to the gravitational influence of Neptune.

In the figure above, in the lower right corner is the orbit of Sedna, a trans-Neptunian object that some astronomers believe to be in the Oort Cloud and others in the scattered disk. It was discovered in 2003 and is the member of the solar system with the longest period known to date.

What does the luminous tail of comets produce?

Comets' tails, their most striking feature when viewed from Earth, forms when they get close enough to the Sun.

The comet's gas particles collide with the current of the solar wind and interact with the highly energetic photons of the Sun, managing to displace them and move them away from the star. That is why we always see that the comet's tail points in the opposite direction to the Sun.

The closer the comet gets to the star, the brighter it becomes. This is why comets are best seen shortly after sunset in the western sky, or shortly before sunrise in the eastern sky.

What shape is the orbit of comets?

The orbits of comets are conical curves, almost always ellipses with great eccentricity. In other words, they are very flattened ellipses, unlike the orbits of the planets, whose eccentricity brings them quite close to the circumference. Sometimes the orbit can even be parabolic or hyperbolic.

The force of gravity exerted by the Sun and the other components of the solar system is responsible for the orbit. And to a lesser extent, the gases that the comet itself gives off.

The orbit of many, many comets brings them quite close to Earth's neighborhood, the so-called inner solar system, but they are almost always only observable through telescopes.

Short period kites

The period of a comet, that is, the time it takes to travel through its orbit, is proportional to its size. There are very short period comets, like the Encke, which takes 3.3 years to visit Earth. It takes between 74 and 79 years for Halley's Comet to be seen again.

These comets are classified as short-period comets, whose orbits take them close to Jupiter or even beyond the orbit of Neptune. It takes less than 200 years to complete. About a dozen of them arrive each year in the inner solar system, but you need a telescope to be able to observe them.

Long period kites

For their part, long-period comets take more than 200 years to travel their path and their orbits are usually parabolic. They are believed to come from the distant Oort Cloud.87

Examples of famous comets

The most famous comets are named after their discoverers. They are also given a name with numbers and letters according to a code established by astronomers, which includes the period and year of discovery.

Here are some of the most notable comets:

Halley's Comet

It is without a doubt the most remarkable comet of all and the best documented. It visits Earth every 75 years or so and numerous chroniclers around the world have recorded its appearance since 240 BC, although they did not realize that it was the same object, until Edmund Halley calculated its orbit and predicted its return.

The 1986 visit was used to directly study its structure through the unmanned Giotto mission. Its core is estimated to be about 15 km wide more or less.

Halley is expected to return to Earth by 2061, however, each time the comet visits us, it leaves its remains scattered around Earth's orbit. The meteor shower known as the Orionids, visible every October, are part of that debris, as well as the Eta-Aquarids, which appear between the months of April and May.

Tempel-Tuttle

The Tempel-Tuttle is famous for being the father of the Leonids, another notable meteor shower. It was discovered in the 19th century and is a short-period comet: it takes 33 years to travel its orbit.

It is not as conspicuous as Halley's Comet, as it is not visible to the naked eye. Their next visit will be in 2031. As Tempel-Tuttle approaches Earth, the Leonids intensify their activity to become meteor storms.

Hale-Bopp

Figure 4. View of Comet Hale-Bopp during its visit in 1997. Source: Wikimedia Commons. Tequask.

This comet visited Earth at the end of the 20th century and is known as the Great Comet of 1997, being visible for little more than a year. Its brightness was unusual, and so was the size of its core: 40 km wide. Many people believed that an alien ship would arrive on Earth along with him.

The study of its light by spectroscopy revealed the presence of organic compounds, a large quantity of heavy water - deuterium oxide - and a notable sodium tail, apart from the tails described in the preceding sections.

It is still observable through large telescopes and its next visit will be 2380 years from now.

Shoemaker-Levy 9

This is the comet notable for having impacted the surface of Jupiter in 1994. It allowed scientists to discover in part the composition of Jupiter's atmosphere, in which sulfur, ammonia, carbon sulfide, and hydrogen sulfide, among other compounds, were found..

References

1. Astronomy for beginners. Comets. Recovered from: astronomia-iniciacion.com.
2. Chodas, P. Introduction to Comets and Asteroids. Recovered from: stardustnext.jpl.nasa.gov.
3. Maran, S. Astronomy for Dummies.
4. Oster, L. 1984. Modern Astronomy. Editorial Reverté.
5. Wikipedia. Kite. Recovered from: es.wikipedia.org.