Based on observations by Bailer-Jones et al. (2018) who propose a close fly-by of the K-type star Gliese 710 in approximately 1.36 Myr we investigate the immediate influence of the stellar passage on trajectories of Oort cloud objects. Using a newly developed GPU-based N-body code (Zimmermann (2021)) we study the motion of 3.6 million testparticles in the outer Solar system where the comets are distributed in three different “layers” around the Sun and the 4 giant planets. We study the immediate influence of Gliese 710 at three passage distances of 12000, 4300, and 1200 au. Additionally, different inclinations of the approaching star are considered. Depending on the passage distance a small number of comets (mainly from the disk and flared disk) is scattered into the observable region (< 5 au) around the Sun. In addition, a huge number of comets (mainly the ones directly in the path of the passing star) shows significant changes of their perihelia. But, they will enter the inner Solar system a long time after the stellar fly-by depending on their dynamical evolution.

Thousands of planets outside the Solar system have been discovered, with exoplanets in different environments. Since we cannot expect to find an exoplanetary system fully resembling our Solar System, we consider a Solar System type configuration where the Earth moves in an eccentric orbit. We focus on young Earth 1 billion years ago, when the Sun’s extreme UV (EUV) flux was about 5 times higher than the current radiation. In case of eccentric motion of Earth, strong variations of the EUV flux would influence the evolution of the planet’s atmosphere (EUV radiation of 50 times the current EUV flux would be possible). Taking into account a certain amount of Nitrogen in the atmosphere of such a young Earth, we study the non-thermal loss of N2 over a long time interval. We therefore investigate to what extent eccentric motion will influence the conditions of habitability of a terrestrial planet.

From the numerous detected planets outside the Solar System, no terrestrial planet comparable with our Earth has been discovered so far. The search for an Exo-Earth is certainly a big challenge which may require the detections of planetary systems resembling our Solar System in order to find life like on Earth. However, even if we find Solar System analogues, it is not certain that a planet in Earth position will have similar circumstances as those of the Earth. Small changes in the architecture of the giant planets can lead to orbital perturbations which may change the conditions of habitability for a terrestrial planet in the habitable zone (HZ). We present a numerical investigation where we first study the motion of test-planets in a particular Jupiter–Saturn configuration for which we can expect strong gravitational perturbations on the motion at the Earth's position according to a previous work. In this study, we show that these strong perturbations can be reduced significantly by the neighbouring planets of Earth. In the second part of our study, we investigate the motion of test-planets in inclined Jupiter–Saturn systems where we analyse changes in the dynamical behaviour of the inner planetary system. Moderate values of inclination seem to counteract the perturbations in the HZ, while high inclinations induce more chaos in this region. Finally, we carry out a stability study of the actual orbits of Venus, Earth and Mars moving in the inclined Jupiter–Saturn systems for which we used the Solar System parameters. This study shows that the three terrestrial planets will only move in low-eccentric orbits if Saturn's inclination is ≤10°. Therefore, it seems that it is advantageous for the habitability of Earth when all planets move nearly in the same plane.

Determining planetary habitability is a complex matter, as the interplay between a planet's physical and atmospheric properties with stellar insolation has to be studied in a self consistent manner. Standardized atmospheric models for Earth-like planets exist and are commonly accepted as a reference for estimates of Habitable Zones. In order to define Habitable Zone boundaries, circular orbital configurations around main sequence stars are generally assumed. In gravitationally interacting multibody systems, such as double stars, however, planetary orbits are forcibly becoming non circular with time. Especially in binary star systems even relatively small changes in a planet's orbit can have a large impact on habitability. Hence, we argue that a minimum model for calculating Habitable Zones in binary star systems has to include dynamical interactions.

The growing number of detected planets in binary star systems requires methods for a quick assessment of possible habitability of planets in such environments. We offer an analytic method to determine habitability of a terrestrial planet in binary star systems. In this context we give an answer to the most important question: Do the radiative and gravitational perturbations of a secondary influence the extent of the habitable zone (HZ)?

After we have defined the borders of the HZ, we will show the dynamical behaviour of a terrestrial planet in the HZ when adding a Jupiter to the system. In such a system the HZ shows signs of mean motion resonances and secular resonances, depending on the architecture of the planetary system.

Up to now, more than 500 extra-solar planets have been discovered. Many of these extrasolar systems consist of one star and only one giant planet. However, recently more and more different types of systems have become known, including also extrasolar planets in binaries. In our study, we will concentrate on such systems, since a large percentage of all G-M stars are expected to be part of binary or multiple stellar systems. Therefore, these kinds of systems are worthy of investigation in detail. In particular, we will concentrate on planets in P-Type motion, where the planet orbits around both stars. During the last few years, four such systems (NN Ser, HW Vir, HU Aqr and DP Leo) have been discovered. In our study, we performed dynamical studies for three multi-planetary systems in binaries (NN Ser, HW Vir, HU Aqr), and compared simulated eclipse timing variations (ETV) to current observational data.

In close eclipsing binaries, measurements of the variations in the binary's eclipse timing may be used to infer information about the existence of planets in P-Type motion. To study the possibility of detecting such planets with CoRoT and Kepler, we calculated eclipse timing variations (ETV) for different values of the mass and orbital elements of the perturbing planet. These investigations are a continuation of the work of Schwarz et al. (2011).

Observations of about 60 binary star systems hosting exoplanets indicate the necessity of stability studies of planetary motion in such multi-stellar systems. For wide binary systems with separations between hundreds and thousands of AU, the results from single-star systems may be applicable but, in tight double stars systems, we have to take the stellar interactions into account which influences the planetary motion significantly.

This review discusses the different types of planetary motion in double stars and the stability of the planets for different binary configurations. An application to the most famous tight binary system (γ Cephei) is also shown. Finally, we analyze the habitability from the dynamical point of view in such systems, where we discuss the motion of terrestrial-like planets in the so-called habitable zone.

Discoveries of extrasolar planets in tight binaries are of great scientific value since these systems can be used to gain new insights in planetary development processes. Gamma Cephei, one of the most thoroughly investigated double star systems is hosting a Jovian planet at a distance of about 2 AU from its primary, a 1.4 solar-mass K1 III-IV star (Neuhäuser et al. 2007; Torres 2007). We comprise aspects of dynamical stability, disc heating processes and different giant planet (GP) formation scenarios in order to gain a better understanding of the open questions that remain in explaining the formation of gamma Cephei b.

There is no doubt that stability studies are of great importance in the fascinating research of extrasolar planetary systems. Even if most of the more than 300 extrasolar planets orbit their host stars as single giant planet and build simple two-body systems, we should not exclude the possibility that these systems could host other (small) planets that have not yet been detected due to obsevational limits. Another aspect to carry out stability studies is the growing interest in the search for extraterrestrial life in the universe. The long-term stability of a planetary system is one of the basic requirements for the evolution of life on a terrestrial planet. In this paper the dynamical behaviour of Earth-like planets will be discussed in single-star single-giant-planet systems, multi-planet systems and binary systems.

Among more than 120 discovered exo-planets, less than 20 were found in double star systems. Out of this sample we studied the planetary motion in those systems that can be regarded as close binaries, i.e. HD41004 AB, $\gamma$ Cephei and Gliese 86. In this study we concentrate on the first two systems, where the secondaries are M4 V dwarfs at about 20 AU from the host-star. A comparison of previous studies – where the dynamical behavior was studied in the (semi-major axis, inclination) plane (see Dvorak et al. 2003a) for $\gamma$ Cephei and Pilat-Lohinger & Funk (2004) for HD41004 A) – shows significant differences in the stability maps. Our numerical investigation examines the region between 0.5 and 1.2 AU, which is influenced mainly by mean motion resonances when the initial position of the detected planet $a_{gp} < 1.5$ AU. If we move the planet farther away from the host-star (to distances $> 1.5$ AU) we observe an arc-shaped chaotic structure in the dynamical map.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html