The concept of the project
As part of the Kepler mission aimed at searching for exoplanets, many interesting objects were discovered during its 4-year observations, the behavior of which has not yet been adequately explained. These include the behavior of the star KIC 8462852, which shows irregular brightness attenuation events that cannot be explained by periodic orbital phenomena. There is currently no definitive answer about the mechanism responsible for the observed phenomena. The idea of the project is to apply the theory of catastrophic thermal destruction of small bodies (comets, asteroids, and the like) to exoplanetary systems that show such irregular brightness attenuation events. We propose a solution to the problem within the framework of the FEB scenario in its extended understanding.

The purpose of the project

To test the plausibility of the theory of catastrophic thermal destruction in the framework of the FEB scenario to explain non-periodic attenuation of the brightness of a star in an exoplanetary system using KIC 8462852 as a testbed.
The main approaches to proposed research
This project offers a solution to the problem of non-periodic attenuation of the brightness of the star KIC 8462852 in the framework of the concept of FEB (falling evaporating bodies) scenario in an extended version. The theory of the physical process of catastrophic thermal destruction was developed at the Fesenkov Astrophysical Institute (Shestakova, Tambovtseva; 1997) in application to the Solar system, considering the processes of falling comets and other small bodies on the Sun. It has been shown that as the body approaches the Sun the stresses inside of it become so high that they exceed the strength limits of a constituent material such as crystalline ice or rock. Once reaching the tensile strength limits, the bodies are destroyed. Also, the formed large fragments continue the process of crushing into smaller parts as they move towards the Sun. Thus, there is not a single event of body disintegration, but a cascading destruction of fragments. The results were presented in the form of an analytical and numerical solution of the thermal diffusion equation. At that time, we were surprised by the result that inside bodies with a radius of 1 km, which have an initial distance to the Sun of 100 AU, the internal tensile stresses exceed the limit of tensile strength of ordinary terrestrial ice at a distance of 40 AU, that is, still outside the region of the large planets.

Objectives of the project
The project goal is achieved by consistently performing the following tasks:
1) Development of the algorithm and search for available initial data for calculations: elastic and thermal parameters, strength limits of materials consisting of silicates and ice, as well as the selection of a range of body sizes and distances from the star.
2) Performing calculations of thermal stresses inside and on the surface of small bodies approaching the star in elongated orbits.
3) Analysis of the results and evaluation of the feasibility of the FEB scenario to explain the observed irregular attenuation of the brightness of a star in an exoplanet system.
The results will allow us to conclude that it is possible to achieve thermal stresses exceeding the strength limits of the material inside small bodies when approaching the star, as a result of which catastrophic destruction of small bodies can occur. The mass of decaying material can become a source of small particles that cause the star’s brightness to decrease.

Expected results.
It will be shown that the destruction of bodies by thermal stresses can occur long before they approach the region of high temperatures, where evaporation becomes possible. This does not require the assumption of unlikely events, such as a collision of bodies. Solutions of the thermal diffusion equation for cometary bodies consisting of crystalline ice will be used. Numerical calculations based on the theory of catastrophic thermal destruction will be performed for a number of specified body sizes and various distances to the star. The required initial size of the body capable to produce enough dust particles to explain the observed decrease in the brightness of the star KIC 8462852 will be determined. Numerical results in the form of thermal stresses inside and on the surface of bodies will be presented. The distances from the star where these bodies will begin to disintegrate will be determined.

Leader : Shestakova L.I. Grant: AP08956243-OT-20. MES RK. 2020-2021