Solar System analogues among exoplanetary systems

Abstract: Over the past two decades many discoveries of exoplanets have been made, which have drawn much attention to extrasolar planetary systems. In this work we study the composition of these systems and search for analogues of the Solar System. We considered the planets in the database at exoplanet.eu. The search of solar-like systems required these planets to be classified. The classification was performed using k-means clustering algorithm and planets with measured masses and semi-major axes were divided into three clusters: hot Jupiters, gas giants and the third cluster with rocky and Neptunian planets. Our first attempt to separate rocky and Neptunian planets by their density was performed by using k-means algorithm for planets with three measured parameters: mass, radius and semi-major axis. The results, however, were not satisfactory and a simple mass limit was chosen instead. Our examination of the extrasolar systems showed that there are few Solar System analogues. This most probably depends on the selection effects of the present-day detection techniques. Two of them were studied more closely: the Doppler radial velocity and transit technique. The first one is more likely to detect massive planets in close orbits, while the latter is more preferable for planets that pass in front of their host stars and have large radii and short orbital periods. Low-mass Earth-like rocky planets are more likely to be detected by the transit technique. Overall, the distribution of planets in their classes has been shown to follow expectations and selection effects. The systems that contain hot Jupiters were studied closely and the results suggest that there is a number of hot Jupiters that might likely be caught in the act of migration. Also, the number of transiting extrasolar Neptunes and Earths was compared to the results presented by Petigura et al. (2013). It revealed a discrepancy, which arose due to the correction of the occurrence rate of these planets made by the article’s authors. Rocky planets that potentially can host life were another interesting subject in the search of Solar System analogues. According to our definition of the habitable zone, we found six super-Earths and one Earth-like planet that might be habitable. However, such conclusions need deeper examination of the planetary properties.