- Asteroid temperature
Asteroids through cold, lifeless bodies. In the distant past, their depths could be warm and even hot due to radioactive or other sources of heat. Since then, they have long since cooled down. However, the internal heat never warmed the surface: the flow of the heat from the bowels was unacceptably small. The surface layers remained cold, and only collisions caused from time to time a short local heating up. The only constant source of heat for the asteroids remains the distant Sun and therefore heating very badly.
The heated asteroid emits heat energy into space, and the more intense it is heated up. Losses are covered by the absorbed part of solar energy falling on the asteroid. If to average temperature on all illuminated surfaces, we receive that at asteroids of the spherical form the average temperature of the illuminated surface in 1, 2 times lower, than the temperature in a sunflower point. Due to the rotation of asteroids, the temperature of their surface quickly is changing. Sun-heated areas of the surface quickly cool down due to low thermal capacity and low thermal conductivity of their components. As a result, the asteroid has a heatwave running along its surface. It quickly fades with depth, without penetrating even a few tens of centimeters into the depth.
Deeper the temperature of the substance is almost constant, the same as in the depths of the asteroid - a few tens of degrees below the average temperature of the sun-lit surface. In the bodies moving in the asteroid ring, it can be taken roughly equal to 100-150 K. No matter how small the thermal inertia of the asteroid surface layers is, if we are to be absolutely strict, we should say that the temperature does not have time to take the equilibrium value with changing lighting conditions.
The morning side, not having time to warm up, is always a little colder than it should be, and the evening side is a little warmer, not having time to cool down. Regarding the sunflower point, there is a slight asymmetry in the distribution of temperatures. The maximum thermal radiation of asteroids lies in the region of wavelengths of about 20 microns.
Therefore, their infrared spectra should look like a continuous radiation with an intensity monotonically decreasing in both directions from the maximum. This is confirmed by observations made by O. Hansen in the range of 8-20 microns. However, when Hansen tried to determine from these observations the temperature of asteroids, it was higher than estimated (about 240K), and the reason for this is still not clear. The low temperature of bodies moving in the asteroid ring means that the diffusion in the asteroid substance is "frozen". Atoms are not capable of leaving their places. Their mutual location has remained unchanged for billions of years. Isolation can cause diffusion to life only in those asteroids that are very close to the Sun, but only in the surface layers and for a short time.
- The composition of the asteroid substance
Meteorites are extremely diverse, as are their parent bodies - asteroids. At the same time, their mineral composition is very scarce. Meteorites consist mainly of iron-magnesium silicates. They are present in the form of small crystals or glass, usually partially recrystallized. The other main component is nickel-plated iron, which is a solid solution of nickel in the iron and, as in any solution, the nickel content in the iron is different - from 6-7% to 30-50%.
Occasionally there is also nickel-free iron. Sometimes significant amounts of iron sulfides are present. Other minerals are in small quantities. It has been possible to identify only about 150 minerals, and although even now they are discovering more and more, it is clear that the number of There are very few meteorite minerals compared to their abundance in the Earth"s rocks, where more than 1, 000 of them have been detected. This testifies to the primitive, undeveloped nature of the meteorite substance.
Many minerals are not present in all meteorites, but only in some of them. Chondrites are the most common among meteorites. These are stone meteorites, ranging in color from light grey to very dark, with an amazing structure: they contain rounded grains - chondromas, sometimes well visible on the surface of the fracture and easily stained with meteorite. The size of chondrons varies from microscopic to centimeter in size. They occupy a considerable volume of meteorite, sometimes up to a half of it, and are poorly cemented by the interchondrion matrix. The composition of the matrix is usually identical to that of the chondroma and sometimes differs from it. As for the origin of chondromas, there are many hypotheses, but they are all controversial.