Asteroids, comets, meteors, meteorites - astronomical objects that seem the same for the uninitiated in the foundations of the science of celestial bodies. In fact, they differ in several ways. The properties that characterize asteroids, comets, meteors, meteorites are easy to remember. They have a certain similarity: such objects are classified as small bodies, often classified as space debris. About what a meteor is, how it differs from an asteroid or comet, what are their properties and origin, and we will discuss below.
Tailed Wanderers
Comets are space objects consisting of frozen gases and stone. They are born in remote areas of the solar system. Modern scientists suggest that the main sources of comets are Kuiper belt and diffuse disk, as well as hypothetically existing Oort cloud.
Comets have strongly elongated orbits. When approaching the Sun, they form a coma and a tail. These elements consist of vaporizing gaseous substances (water vapor, ammonia, methane), dust and stones. The head of a comet, or coma, is a shell of the smallest particles, characterized by brightness and visibility. It has a spherical shape and reaches its maximum size when approaching the Sun at a distance of 1.5-2 astronomical units.
At the front of the coma is the nucleus of the comet. It, as a rule, has a relatively small size and an elongated shape. At a considerable distance from the Sun, the core is all that remains of the comet. It consists of frozen gases and rocks.
Types of comets
The classification of these cosmic bodies is based on the frequency of their rotation around the luminary. Comets flying around the Sun in less than 200 years are called short-period ones. Most often, they enter the inner regions of our planetary system from the Kuiper belt or the scattered disk. Long-period comets handle a period of more than 200 years. Their "homeland" is the Oort cloud.
"Minor planets"
Asteroids are made up of hard rock. In size, they are much inferior to planets, although some representatives of these space objects have satellites. Most of the minor planets, as they were called before, are concentrated in the Main asteroid belt, located between the orbits of Mars and Jupiter.
The total number of such cosmic bodies known for 2015 exceeded 670 thousand. Despite such an impressive number, the contribution of asteroids to the mass of all objects in the solar system is insignificant - only 3–3.6 * 10 21 kg. This is only 4% of the same parameter of the moon.
Not all bodies of small size are referred to asteroids. The selection criterion is the diameter. If it exceeds 30 m, then the object is referred to as asteroids. Smaller bodies are called meteoroids.
Asteroid Classification
A grouping of these cosmic bodies is based on several parameters. Asteroids combine the features of their orbits and the spectrum of visible light that was reflected from their surface.
According to the second criterion, three main classes are distinguished:
- carbon (C);
- silicate (S);
- metal (M).
Approximately 75% of all asteroids known today belong to the first category. With the improvement of equipment and a more detailed study of such objects, the classification expands.
Meteoroids
A meteoroid is another type of cosmic body. These are not asteroids, comets, meteors or meteorites. A feature of these objects is their small size. Meteoroids in their dimensions are located between asteroids and cosmic dust. Thus, they include bodies with a diameter of less than 30 m. Some scientists define the meteoroid as a solid with a diameter of 100 ÎĽm to 10 m. By their origin, they are primary or secondary, that is, formed after the destruction of larger objects.
Upon entering the Earth's atmosphere, the meteoroid begins to glow. And here we are already approaching the answer to the question of what a meteor is.
Shooting star
Sometimes among the flickering stars in the night sky, one suddenly flares up, describes a small arc and disappears. Whoever has seen such a thing at least once knows what a meteor is. These are “shooting stars” that have nothing to do with real stars. A meteor is actually an atmospheric phenomenon that occurs when small objects (those meteoroids) that enter the planet’s air shell are small. The observed flash brightness directly depends on the initial dimensions of the cosmic body. If the brightness of the meteor exceeds the fifth magnitude, it is called a car.
Observation
Such phenomena can only be admired from planets with an atmosphere. Meteors on the moon or on Mercury cannot be observed, since they lack an air shell.
Under suitable conditions, “shooting stars” can be seen every night. It is best to admire meteors in fine weather and at a considerable distance from a more or less powerful source of artificial lighting. Also, there should not be a moon in the sky. In this case, it will be possible to notice with the naked eye up to 5 meteors per hour. Objects leading to the appearance of such single “shooting stars” revolve around the Sun in a variety of orbits. Therefore, the place and time of their appearance in the sky cannot be accurately predicted.
Streams
Meteors, photos of which are also presented in the article, as a rule, have a slightly different origin. They are part of one of several swarms of small cosmic bodies orbiting the star along a specific path. In their case, the ideal period for observation (the time when, looking at the sky, anyone can quickly understand what a meteor is) is pretty well defined.
A swarm of similar space objects is also called a meteor shower. Most often, they are formed during the destruction of the comet's nucleus. Individual particles of the swarm move parallel to each other. However, from the surface of the Earth it seems that they fly out of a certain small area of ​​the sky. This section is called the flow radiant. The name of the meteor swarm is usually given by the constellation in which its visual center (radiant) is located, or by the name of the comet, the decay of which led to its appearance.
Meteors, whose photos are easy to obtain with special equipment, belong to such large streams as Perseids, Quadrants, eta Aquarids, Lirids, Geminids. In total, 64 streams have been recognized to date and about 300 more are awaiting confirmation.
Heavenly stones
Meteorites, asteroids, meteors and comets are related concepts according to certain criteria. The first are space objects that have fallen to Earth. Most often, their source is asteroids, less often comets. Meteorites carry invaluable data on various corners of the solar system outside the Earth.
Most of these bodies that hit our planet are very small. The most impressive meteorites in size leave traces after the impact, quite noticeable even after millions of years. Well-known is the crater near the city of Winslow in Arizona. The fall of the meteorite in 1908 allegedly caused the Tunguska phenomenon.
Such large objects "visit" the Earth once every several million years. Most of the meteorites found are quite modest in size, but do not become less valuable to science.
According to scientists, such objects can tell a lot about the time of formation of the solar system. Presumably, they carry particles of matter from which young planets consisted. Some meteorites come to us from Mars or the Moon. Such space wanderers allow you to learn something new about neighboring objects without the huge cost of distant expeditions.
To remember the differences of the objects described in the article, we can summarize the transformation of such bodies in space. An asteroid consisting of solid rock, or a comet, which is an ice block, when destroyed, generates meteoroids, which, when they enter the planet’s atmosphere, flare up by meteors, burn up in it or fall, turning into meteorites. The latter enrich our knowledge of all previous ones.
Meteorites, comets, meteors, as well as asteroids and meteoroids are participants in the continuous space movement. Studying these objects makes a great contribution to our understanding of the structure of the Universe. As the equipment of astrophysics improves, more and more data about such objects are obtained. The relatively recent mission of the Rosetta probe clearly demonstrated how much information can be obtained from a detailed study of such cosmic bodies.