Asteroids are called cosmic bodies that are not satellites of planets, the mass of which is insufficient for such an object to acquire a spherical shape characteristic of a dwarf or ordinary planet under the influence of its own gravity.
When examining any such body, one of the first tasks is to answer the question of what the asteroid is made of, since the compositional features shed light on the origin of the object, which is ultimately connected with the history of the entire solar system. From a practical point of view, the potential suitability of asteroid bodies in terms of future use of their resources is of interest.
How do we know about the composition of asteroids
With varying degrees of accuracy, it is possible to judge the chemistry and mineralogy of asteroids based on various direct and indirect research methods:
- Approximately estimate the composition of the object will help the position of its orbit in the solar system. As a rule, the farther from the Sun a smallspace body, the more volatile substances in its composition, in particular, water ice.
- An important role in resolving the issue is played by the spectral characteristics of the asteroid. However, the analysis of the reflected spectrum still does not allow one to judge unambiguously which substances predominate in the composition of a given body.
- Study of meteorites - fragments of asteroids falling on the Earth's surface, makes it possible to accurately determine their mineral and chemical composition. Unfortunately, the origin of the meteorite is not always known.
- Finally, the most complete data on what an asteroid consists of can be obtained by analyzing its rocks using an interplanetary automatic apparatus. To date, several objects have been investigated by this method.
Classification of asteroids
There are three main types into which asteroids are divided by composition:
- C - carbon. These include the majority of known bodies - 75%.
- S - stone, or silicate. This group includes about 17% of asteroids discovered to date.
- M - metal (iron-nickel).
These three main categories include objects of different spectral classes. In addition, there are several groups of rare asteroids that differ in one or another feature of the spectrum.
The above classification is constantly becoming more complex and detailed. In general, spectral data alone, of course, is not enough to establish what asteroids are made of. The description of the composition is extremely complextask. After all, although the differences in the spectra definitely indicate differences in the surface material, there can be no certainty that the composition of objects of the same class is identical.
Near-Earth Objects
Near-Earth or near-Earth asteroids are called asteroids whose orbital perihelion does not exceed 1.3 astronomical units. Special space missions were sent to study some of them.
- Eros is a relatively large body with dimensions of approximately 34×11×11 km and a mass of 6.7×1012 t, belonging to class S. This stony asteroid was studied in 2000 NEAR Shoemaker. In addition to silicate rocks, it contains about 3% of metals. These are 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 3.5×107 t. Dust from the surface of Itokawa was delivered to Earth by the return capsule of the Japanese Hayabusa probe in 2010. Dust particles contain minerals of the olivine, pyroxene, and plagioclase groups. The Itokawa soil is characterized by a high percentage of iron in silicates and a low content of this metal in free form. It has been established that the substance of the asteroid was subjected to thermal and impact metamorphism.
- Ryugu, a class C asteroid, is currently being studied by the Hayabusa-2 spacecraft. It is believed that the composition of such bodies has not changed much since the formation of the solar system, so the study of Ryugu is of great interest. Deliverysamples, which will allow a more detailed study of what the asteroid is made of, are planned for 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. The Bennu soil is expected to be delivered to Earth for detailed study in 2023.
What does the asteroid belt consist of
The area between the orbits of Mars and Jupiter, within which a large number of objects of various composition, origin and size are concentrated, is commonly called the Main Belt. In addition to the actual asteroids of various types, it includes cometary bodies and one dwarf planet - Ceres (previously 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 that has been 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 meteorites originating from it helps to clarify the knowledge of what the asteroid Vesta 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 the most ancient bodies here. Silicates may have a different history, but their material has already undergone some metamorphosis as part of large or small objects. Metallic asteroids such as Psyche or Cleopatra are obviously fragments of the cores of already formed protoplanets.
Asteroids distant 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 extensive than the Main Belt. The main difference between the two is what Kuiper belt asteroids are made of. 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. In terms of properties, they are already in many ways similar to comets.
Intermediate position between the Kuiper belt objects and the Main Belt asteroids is occupied by centaurs moving along unstable trajectories between the orbits of Jupiter and Neptune. They differ in their transition 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, cob alt 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 addition to iron and nickel, the specified metals. In addition, in the composition of C-asteroids that have not undergone differentiation, the distribution of elements is quite uniform.
Using these considerations, companies declaring their desire to develop asteroids periodically stir up interest in the topic. For example, in July 2015, the media reported a close flyby of the platinum asteroid 2011 UW158. The estimate of its reserves reached more than five trillion dollars, but it turned out to be clearly exaggerated.
Nevertheless, there are still valuable raw materials on asteroids. The question of the expediency of its development rests on such problems as a reliable assessment of reserves, the cost of flights and production, and, of course, the required technological level. In the short term, these tasks can hardly be solved, so humanity is still very far from the development of asteroids.
