Asteroids are called cosmic bodies that are not satellites of planets, the mass of which is insufficient so that under the influence of their own gravity such an object acquires a spherical shape characteristic of a dwarf or ordinary planet.
In the study of any such body, one of the first tasks is to answer the question of what the asteroid consists of, since the compositional characteristics shed light on the origin of the object, which is ultimately connected with the history of the entire solar system. On the practical side, the potential suitability of asteroid bodies from the point of view of the use of their resources in the future is of interest.
How do we know about the composition of asteroids
It is possible to judge the chemistry and mineralogy of asteroids with varying degrees of accuracy on the basis of various direct and indirect research methods:
- The position of its orbit in the solar system will help to approximately evaluate the composition of an object. As a rule, the farther away from the Sun a small cosmic body is, the more volatile substances, in particular, water ice, are in its composition.
- An important role in solving the problem is played by the spectral characteristics of the asteroid. However, analysis of the reflected spectrum still does not allow us to judge unambiguously which substances predominate in the composition of a given body.
- The study of meteorites - fragments of asteroids falling on the Earth's surface, makes it possible to accurately establish their mineral and chemical composition. Unfortunately, the origin of the meteorite is far from always known.
- Finally, the most complete data on what an asteroid consists of can be obtained by analyzing its rocks using an interplanetary automatic vehicle. To date, several objects have been investigated using this method.
Asteroid Classification
The main types into which asteroids are divided in composition are three:
- C is carbon. Most of the known bodies belong to them - 75%.
- S - stone, or silicate. This group includes about 17% of currently discovered asteroids.
- M - metal (iron-nickel).
These three main categories include objects of different spectral classes. In addition, several groups of rare asteroids are distinguished, which differ in certain spectral features.
The given classification is constantly complicated and detailed. In general, spectral data alone, of course, are not enough to establish what asteroids consist of. Description of the composition is an extremely difficult task. Indeed, although differences in spectra definitely indicate differences in surface material, there can be no certainty that the composition of objects of the same class is identical.
Near Earth Objects
Near-Earth or approaching Earth are called asteroids whose perihelion of the orbit does not exceed 1.3 astronomical units. Special space missions were sent to study some of them.
- Eros is a relatively large body measuring approximately 34 × 11 × 11 km and weighing 6.7 × 10 12 tons, belonging to the class S. This stone asteroid was studied in 2000 by the NEAR Shoemaker. In addition to silicate rocks, it contains about 3% metals. It is mainly iron, magnesium, aluminum, but there are also rare metals: zinc, silver, gold and platinum.
- Itokawa is also an S class asteroid. It is small - 535 × 294 × 209 m - and has a mass of 3.5 × 10 7 tons. Dust from the surface of Itokawa was brought to Earth by the returned capsule of the Japanese Hayabusa probe in 2010. Dust particles contain minerals of the olivine, pyroxene and plagioclase groups. Itokawa soil is characterized by a high percentage of iron in silicates and a low free metal content of this metal. It was established that the substance of the asteroid was subjected to thermal and shock metamorphism.
- Ryugu, a class C asteroid, is currently being studied by the Hayabusa-2. It is believed that the composition of such bodies has not changed much since the era of the formation of the solar system, so the study of Ryugu is of great interest. Delivery of samples, which will allow a more detailed study of what the asteroid consists of, is planned at the end of 2020.
- Bennu is another object near which the space mission is currently operating - the OSIRIS-Rex station. This special-class B carbon asteroid is also regarded as a source of important knowledge about the history of the solar system. Soil Bennu is supposed to be delivered to Earth for a detailed study in 2023.
What the asteroid belt consists of
The area between the orbits of Mars and Jupiter, within which a large number of the most diverse in composition, origin and size of objects is concentrated, is usually called the Main belt. In addition to all kinds of asteroids themselves, it includes cometary bodies and one dwarf planet - Ceres (earlier it was referred to as asteroids).
Today, as part of the Dawn mission, one of the largest objects of the belt, Vesta, has been studied in sufficient detail. It, in all likelihood, is a protoplanet, preserved since the formation of the solar system. Vesta has a complex structure (has a core, mantle and crust) and a rich mineral composition. It belongs to a special spectral class V of predominantly silicate asteroids with a high content of magnesium-rich pyroxene. The study of the meteorites originating from it helps to refine the knowledge of what the West asteroid consists of.
In general, the asteroid belt is a collection of bodies that demonstrate the state of matter in the solar system at different stages of its formation. Carbon asteroids - for example, Matilda - represent here the most ancient bodies. Silicate may have a different history, but their material has already undergone some metamorphization as a part of large or small objects. Metallic asteroids, such as Psyche or Cleopatra, are obviously fragments of the nuclei of already formed protoplanets.
Asteroids Far From The Sun
Another large-scale collection of small bodies is the Kuiper belt, located beyond the orbit of Neptune. It is much more massive and vast than the main belt. The main difference between the two is what constitutes the Kuiper belt asteroids. They contain much more volatile components - water ice, frozen nitrogen, methane and other gases, as well as organic substances. These bodies are even closer in composition to the protoplanetary cloud. By properties, they are already in many ways similar to comets.
An intermediate position between the Kuiper belt objects and the asteroids of the Main belt is occupied by centaurs moving along unstable trajectories between the orbits of Jupiter and Neptune. They differ in transitional composition.
About development prospects
Asteroids have long attracted attention as a potential source of rare and precious metals: osmium, palladium, iridium, platinum, gold, as well as molybdenum, titanium, cobalt and others. The arguments in favor of mining them on asteroids are based on the fact that the earth's crust is poor in heavy elements due to gravitational differentiation. It is assumed that as a result of the same process, M-asteroids are rich in these metals, in addition to iron and nickel. In addition, the distribution of elements not subjected to differentiation of C-asteroids is fairly uniform.
Using these considerations, companies declaring their desire to develop asteroids periodically fuel interest in the topic. For example, in July 2015, the media circumvented a message about the near passage of a platinum asteroid 2011 UW 158 . The estimate of its reserves reached up to more than five trillion dollars, but it was clearly exaggerated.
Nevertheless, valuable raw materials on asteroids are still there. The question of the appropriateness of its development rests on such problems as reliable estimation of reserves, the costs of flights and production, and, of course, the necessary technological level. In the short term, these tasks can hardly be solved, therefore, mankind is still very far from the development of asteroids.