Chaotic streams and risks for Earth due to passing stars

In about 1.3 million years a passing star will cross the outermost region of our solar system, i.e. the Oort cloud. This stellar fly-by will certainly cause chaos in this region due to gravitational perturbation. In addition, it will trigger cometary streams towards the Sun and might thus increase the risk of collisions of comets with planet Earth. All these processes will be studied in detail in the framework of this FWF- project with the aim to get estimates for the probability of our home planet experiencing stronger bombardments in the future. The science of this project comprises the following studies. STELLAR FLY-BY Observations of the European space mission GAIA have shown that the K-type star Gliese 710 is approaching our solar system and will enter the Oort cloud at a distance to the Sun between 600 billion and 1800 billion kilometers. The Oort cloud is known as reservoir of billions of comets. Thus, it is quite obvious that a star which enters this reservoir of comets will trigger cometary streams towards the Sun and enhances the probability of impacts of small bodies with planet Earth. However, GAIA did not observe low-mass stars (M-type stars), which are the majority in the solar neighborhood (90 %). To estimate the threat of these stars when potentially passing the solar system, we extend our investigation of stellar encounters to M-type stars and to the even smaller Brown Dwarfs in order to provide a more extensive overview about the risk of impacts on planet Earth due to stellar fly-bys. CHAOS IN THE OUTER REGION OF OUR PLANETARY SYSTEM Chaos originated by a stellar encounter in the outer region of the solar system affects mainly comets of the Oort cloud and of the Kuiper belt. Our numerical simulations will study to what degree do stellar fly-bys and triggered cometary streams enhance chaos in the motion of planetesimals in the solar system and how does this increase the risk of collisions of small bodies with planet Earth. We also analyze the influence of the giant planets (Jupiter, Saturn, Uranus and Neptune) and pay special attention to the big Kuiper belt objects (e.g. Sedna or Eris) discovered so far and the still undetected Planet 9. These numerical studies will help to get estimates for the degree of chaos in the outer solar system caused by a stellar fly-by. COLLISIONS OF COMETS AND ASTEROIDS Cometary streams entering the main belt of asteroids between Mars and Jupiter might lead to collisions between comets and asteroids. Such interactions will be studied in detail in the framework of this project where we combine dynamical evolution and realistic collision simulations for the first time. In this context we will verify in which way the so-far unknown small asteroids which will be discovered by the Large Synoptic Survey Teleskop LSST (also known as Rubin Observatory) in the near future influence our collision study for planet Earth.