Terrestrial Planet Formation and Water Delivery around Low Mass Stars

AGUSTIN DUGARO; LUCIANO A.DARRIBA; GONZALO CARLOS DE ELIA

Foz de Iguazu

Simposio; "nd COSPAR Symposium: Water and Life in the Universe; 2015

Several studies have been developed in order to analyze the efficiency of planetary formation around low-mass stars.In particular, Raymond et al. (2007) performed N-body simulations in order to study the process of terrestrial planetformation for stellar masses ranging from 0.2 Msun to 1 Msun. To do this, the authors assumed that the mass of theprotoplanetary disk is proportional to the stellar mass, so that, the smaller the mass of the star, the smaller themass of the disk.In this framework, Raymond et al. (2007) showed that the terrestrial planets formed in the habitable zone (HZ)around stars with masses M < 0.6 Msun are small (< 0.1 Mearth) and dry, namely, with very low water contents. In fact, inagreement with these authors, such stars have low-mass protoplanetary disks and therefore, the radial mixing of materialand the water delivery are inefficient processes.During the last years, Andrews et al. (2010) analyzed the emission from 16 protoplanetary disks around stars with masses between0.3 Msun and 2 Msun located in the Ophiuchus star-forming region. These authors studied the structure of such disks and suggestedthat their masses are comparable and even higher than that associated with the Minimum Mass Solar Nebula (MMSN)(Hayashi 1981).In particular, Andrews et al. (2010) inferred the existence of a 0.143 Msun disk around GSS 39, which is a M-type star with0.6 Msun.The main goal of our work is to study the process of planetary formation around low-mass stars assuming protoplanetary diskswith a wide range of masses. In particular, we propose to study M0 and M3 type stars, which have masses of 0.5 Msun and 0.29 Msun,respectively. For each stellar target, we consider disks with 5 % and 10 % of the mass of the star. In particular, thepresent study focuses on planets formed in the HZ and their orbital evolution.For each scenario of work, a semi-analytical was used in order to determine the distribution of embryos and planetesimalsat the end of the gaseous phase. Then, these distributions were used as initial conditions for the N-body simulations. For eachstar, we carried out ten N-body simulations for each disk under consideration.Our results suggest the formation of terrestrial planets in the HZ of the resulting systems with a wide range of masses and watercontents. For M3-type stars, planets formed in the HZ have masses between 0.07 Mearth and 0.32 Mearth and water contents of about0.01 %-23 % by mass. For M0-type stars, planets produced in the HZ present masses ranging from 0.28 Mearth to 1.43 Mearth and watercontents of about 18 %-45 % by mass. These planets are likely to retain a substantial and long-lived atmosphere and ongoingtectonic activity probably required to sustain life.We consider that the present work allow us to clarify our understanding about the potential habitability in planetary systemsaround low-mass stars.