What is a comet? The structure of comets. Research using spacecraft

Fascinating celestial objects that have both frightened and fascinated starlets throughout history. There's a lot we don't know about these icy visitors, but here's a breakdown of what scientists have confirmed or strongly suspect about the different types of these so-called "dirty snowballs."

A comet is an icy ball of frozen gas, rock and dust that orbits the Sun in an elliptical path. When closer to the Sun in orbit, the comet's nucleus releases gases that form the coma and tail, so when the comet is far from the Sun, it will not have a tail. The debris left behind by a comet's tail is what causes meteor showers.

Comets are thought to have formed 6 billion years ago, when the solar system was young and just after the formation of the planets. Because comets are so old, scientists believe they may have solutions to puzzles about the nature and evolution of our solar system.

This illustration shows comets racing towards the star Eta Corvi. One comet is shown crashing into a rocky body, throwing dust into space, rich in ice and carbon, and breaks water and organic matter onto the planet's surface. What are the different types of comets? Classifying comets is an ongoing process. Comets can be distinguished by their orbits, which vary greatly. Long-term comets are on tracks that are carried past the planets of the solar system before their return. Scientists suspect that long-period comets originated in the Oort Cloud, located at the edge of our solar system, while short-period comets escaped from the Kuiper Belt, home of Pluto.

Objects can escape from these areas when gravitational changes occur. Halley's Comet is a famous example of a short-period comet with an orbit of only 75 or 76 years. Speaking of Halley's comet, it is believed that two subgroups of short-period comets, Halley's and Jupiter-type comets. This suggests that long period comets may become short-period comets depending on how planetary gravity shapes their orbits. Single-occurrence comites are considered comets that are not associated with the sun and can exit the solar system.

Sunrazing comets are often ill-fated comets that suffer from the Icarus problem. Dead comets, such as recent and misnamed ones, are comets whose gases have burned off. Exocomites are comets that exist outside of our solar system.

How many comets are there? The short answer is a whole bunch. While a comet may be a rare sight in the sky, they are quite well represented in space. Imagine what these icy objects could say, since they highly believe it in space. As soon as a comet enters the central solar system, the surface of this “dirty snowball” heats up. As a result, the frozen substance evaporates directly to gas. Thus, the so-called core develops around the nucleus. Together, the nucleus and coma form the cometary head.

Some comets approach the sun, and they plunge into the solar corona for some time. Its perimeter is less than 1.5 million kilometers. Often they split into several parts, which then continue to fly in parallel almost on the same runway. This corresponds to about one thousandth the density that exists today in the best possible high vacuum. Therefore there is no danger if the earth invades the tail or even the coma of the comet.

Research using spacecraft

It's just that an unlikely collision with a cometary nucleus would have the same adverse effects as asteroid collisions. In addition, each comet is given a different name, which indicates the date of discovery. In this way, the year number is set, and then a capital letter, each of which makes up a half month. Once you have additional information about comet tracks that are difficult to calculate, one of the following five letters is added before this designation.

As spectacular as a comet may seem, as romantic and beautiful as it may seem on those starry summer nights, the comet is actually a huge dirty ball of snow, dirt and ash. So much so that they are commonly referred to as "dirty snowballs" and are essentially made up of 4 main elements: dust, ice, carbon content such as tar, and basically a massive giant rocky center.

They themselves are remnants from star and planet formation processes that arose billions of years ago, which is truly fascinating. Before collapsing around it, countless comets that, with their characteristic bright tails, pass through our solar system are born as huge chunks of rock and floating ice in what is commonly called the Oort cloud.

Oort cloud and comet characteristics

The Oort Cloud is a majestic cloud of comets and asteroids that lies at the edges of the solar system, approximately 1 light year from the Sun. Although the existence of this cloud is hypothetical, it would contain billions of comets and asteroids floating nearly a quarter of a light year away from the star Proxima Centauri.

When big body passes close enough to this cloud and has the appropriate gravitational forces, huge pieces of ice and rocks break off the cloud and rush towards the Sun. As they approach them, they begin to melt, leaving a trail of melting ice behind it, away from the heat source, in a gaseous trail pushed by the solar wind.

The gravity of ours, every planet and every star is the reason they are in constant motion. In the solar system, the gravity of the Sun is the greatest force that influences its movements, the closer it is to it, the greater its speed and the more longer tail or the trail he leaves on his way, like more quantity ice evaporates.

There are two different types of comet tails: those made of dust and those made of ionic gases. The powder tail is usually yellow and contains fine particulate matter. When sunlight hits these small particles, gently pushing them away from the comet's nucleus, this dust tail is formed. Finally, since the pressure of sunlight is relatively weak according to the distance it is located, the dust particles form a curved and diffuse tail.

On the other hand, the tail of ion gases, usually blue, is formed when ultraviolet sunlight strips one or more electrons from the gas atoms in the comet in a process known as ionization. The solar wind carries and pushes these ions away from the comet, leaving a bluish colored tail.

What are comets and how are they studied?

Very interesting, isn't it? What else do you know about comets? Have you ever seen him? From the gravel pile model, the following considerations can be made. Having delineated the characteristics of his model, Whipple begins to analyze the melting and boiling points of the molecules responsible for the formation of coma. As the core approaches perihelion, the increase in solar irradiation in turn increases the surface temperature of the surface exposed to the Sun. Thus, it causes the evaporation of ice and its dispersion in the surrounding space.

In addition, meteoric material below a certain size limit is expelled due to the low gravitational pull of the core, resulting in the formation of a dust tail. One can also check that any larger or higher density of particles may disappear due to thermal shock, but they will generally remain on the surface. Thus, an insulating layer is formed, which is responsible for reducing the loss of gas flow at successive stages of the comet.

However, it should be borne in mind that if the meteoric material was coarse aggregate and poorly cemented, the thermal conductivity would be very low due to the small contact surface between particles. This would mean a reduction in heat transfer coefficient by a factor of 10 compared to that of a solid, making this form of heat transfer ineffective. The most effective mechanism for transferring solar heat from the surface of the core to its interior appears to be radiation at low temperatures.

Thus, the interior of the comet's nucleus will always be extremely cold, not only because of the low thermal conductivity described, but also because the available heat is involved in evaporation. This is a very efficient cooling mechanism in a vacuum. In addition to the production and maintenance of coma during perihelion passage, we will see three other important facts for which the previous model was inadequate.

The extremely high heat should sublimate all the absorbed gas and most its meteoric material. On the other hand, tidal forces would easily destroy the small bodies that make up the core. The gravel mound structure cannot absorb new materials to replace those excluded in the previous stage, given the very low availability offered by interplanetary space. Therefore, the comet must have appeared several times before its appointment with the necessary content of volatile substances. Non-gravitational movement of comets. The model that was considered valid before Whipple does not explain how some comets anticipate their return to perihelion and others, on the contrary, they delay it. Meanwhile, Halley is delayed for about 4 days.

• The presence of comets is usually called sunrasors.
• They are very close to the Sun, but do not disintegrate completely.
• The presence of periodic comets.

Comets: The Dirty Snowballs of the Solar System

A compact body the size of a comet's nucleus succeeds when it passes through the Sun's vicinity without completely evaporating, since it only consumes the thin outer layer. It is possible that core fractures may occur, as in Ikea-Seki, but not complete dispersion. If the core is composed primarily of ice, there is no need to replace the sublimated material that causes coma in orbit. The estimated mass of the cometary nucleus can, in fact, account for the multiple stages of periodic comets. The reason for the non-gravitational motion of comets can be identified with the force of the reaction with the ejection of gas from the nucleus. In the gravel heap model, the calculation did not take into account that the gas released could have sufficient intensity. On the other hand, in the Whipple model, the thermal velocity of the ejection of nuclear molecules, as a consequence of the sublimation of ice, can justify the rocket effect. At Halley, Giotto's probe discovered true plumes of gas and dust escaping through cracks in the surface crust of the core, on the opposite side of the Sun. The advancement or retardation of the comet's return to perihelion can be explained by appealing to this rocket effect and the presence of rotation in the nucleus. In short, a comet is essentially composed of a core of agglomerate of ice and dust, internal structure which is unknown to us and which revolves around the Sun.