CHANGES IN TEMPERATURE AND PRESSURE IN THE ATMOSPHERE OF PLUTO

The dwarf planet Pluto has a shape close to spherical with an equatorial diameter of 2374 km. It moves around the Sun in a very elongated orbit, passing at perihelion from it at a distance of 29.657 AU and at aphelion at a distance of 48.87 AU. Moreover, for almost 20 years, Pluto has been closer to the Sun than the giant planet Neptune. The last time it was from 1979 to 1999. The direction of its rotation around its axis is reverse, a day there lasts 6.387 Earth days with an inclination of its axis of rotation to the plane of the orbit of more than 120°. This is the reason why the seasons on Pluto should be more pronounced than on our Earth. As of 2025, its North Pole is facing the Sun. Its surface temperature varies seasonally from 33 K at aphelion to 60 K at perihelion. Under such conditions, water, nitrogen N2, methane CH4, carbon monoxide CO and their derivatives are frozen. Pluto's thin atmosphere consists mainly of nitrogen, and also of methane and carbon monoxide. All of them are in equilibrium with their frozen forms on the surface. And as Pluto moves away from the Sun, a significant part of its atmosphere freezes in winter, and remains frozen for more than a hundred years. In summer, near perihelion, the surface heats up and releases nitrogen, methane and carbon monoxide. The pressure on Pluto's surface varies seasonally in the range from 0.6 to 2.4 Pa. Analysis of observational data obtained by the "New Horizons" space probe made it possible to follow changes in the thickness and measure the composition of Pluto's atmosphere. Pluto's troposphere turned out to be a boundary layer about 4 km thick, which had a temperature of about 37 K when measured. It is believed that this boundary layer consists of gas that has just evaporated from the planet's surface and has not had time to mix with the rest of the atmosphere. The stratosphere begins above the boundary layer. In it, the temperature increases rapidly with altitude. Moreover, the rate of increase differs in different places above the surface of Pluto from 2.2 K/km to 15 K/km. Such an increase in temperature may be the result of the methane-induced greenhouse effect. The maximum value of 100110 K was reached in the stratopause at altitudes of 20-40 km. And then the temperature slowly decreased at a rate of about 0.2 K/km. The reason for this decrease may be the cooling effect of hydrogen cyanide, acetylene and carbon monoxide. At an altitude of more than 500 km from the surface, the temperature reached 70 K, and then practically did not change. According to the results of star coverage, small vertical inhomogeneities of temperature changes in the atmosphere of Pluto were found, estimated at 0.50.8 K at altitudes of several kilometers. The calculations performed showed that the atmosphere, despite the small pressure value near the surface of Pluto, is able to significantly smooth out the daily changes in these temperatures. Observations showed that from 1988 to 2015, the pressure value gradually increased almost threefold. The use of radio waves in the atmosphere made it possible to determine that in 2015 the pressure near the surface was 1 Pa. The results of the calculations also showed that the value of the so-called pressure scale in Pluto varies significantly with altitude. For the atmospheric layer near the surface, the value of this height scale was estimated at 17-19 km, while for heights of 30-100 km, the height scales were estimated at 50-70 km.