Terrestrial planets and water delivery around low-mass stars

¹ Instituto de Astrofísica de La Plata, CCT La Plata-CONICET-UNLP Paseo del Bosque S/N, 1900 La Plata, Argentina
e-mail: adugaro@fcaglp.unlp.edu.ar
² Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata Paseo del Bosque S/N, 1900 La Plata, Argentina
³ Universidad Nacional de La Patagonia Austral, Unidad Académica Caleta Olivia Ruta 3 Acceso Norte, 9311 Caleta Olivia, Santa Cruz, CONICET, Argentina

Received: 20 February 2016
Accepted: 8 September 2016

Abstract

Context. Theoretical and observational studies suggest that protoplanetary disks with a wide range of masses could be found around low-mass stars.

Aims. We analyze planetary formation processes in systems without gas giants around M3- and M0-type stars of 0.29 M_⊙ and 0.5 M_⊙, respectively. In particular, we assume disks with masses of 5% and 10% of the mass of the star. Our study focuses on the formation of terrestrial-like planets and water delivery in the habitable zone (HZ).

Methods. First, we use a semi-analytical model to describe the evolution of embryos and planetesimals during the gaseous phase. Then, a N-body code is used to analyze the last giant impact phase after the gas dissipation.

Results. For M3-type stars, five planets with different properties are formed in the HZ. These planets have masses of 0.072 M_⊕, ~0.13 M_⊕ (two of them), and 1.03 M_⊕, and have water contents of 5.9%, 16.7%, 28.6%, and 60.6% by mass, respectively. Then, the fifth planet formed in the HZ is a dry world with 0.138 M_⊕. For M0-type stars, four planets are produced in the HZ with masses of 0.28 M_⊕, 0.51 M_⊕, 0.72 M_⊕, and 1.42 M_⊕, and they have water contents of 26.7%, 45.8%, 68%, and 50.5% by mass, respectively.

Conclusions. M3- and M0-type stars represent targets of interest for the search of exoplanets in the HZ. In fact, the Mars-mass planets formed around M3-type stars could maintain habitable conditions in their early histories. Thus, the search for candidates around young M3-type stars could lead to the detection of planets analogous to early Mars. Moreover, Earth-mass planets should also be discovered around M3-type stars and, sub- and super-Earths should be detected around M0-type stars. Such planets are very interesting since they could maintain habitable conditions for very long.