Characterizing the possible interior structures of the nearby Exoplanets Proxima Centauri b and Ross-128 b

Abstract

ABSTRACT We developed a new numerical model to constrain the interior structure of rocky Exoplanets, and applied it to the nearby planets Proxima Centauri b and Ross-128 b. The recently measured elemental abundances of red dwarfs and Alpha Centauri were utilized to infer the bulk composition of each planet, and to measure their core mass fractions (CMFs). The results of our model predicted that the radius of Proxima b at its minimum mass may be 1.036 ± 0.040 R⊕, and if its mass is as high as 2 M⊕, 1.170 ± 0.040 R⊕. The radius of Ross-128 b at minimum mass may be 1.034 ± 0.040 R⊕, with its radius at an upper bound mass of 2 M⊕ being 1.150 ± 0.040 R⊕. Both planets may have thin mantles with similar conditions to Earth, but not convecting as vigorously. The CMFs might lie in the ranges of 20–59 per cent and 34–59 per cent for Proxima b and Ross-128 b, respectively, making it very likely they have massive iron cores. Their central temperatures may be high enough to partially melt the cores, and possibly generate magnetic fields. If they have magnetic fields at present, they are most likely to be multipolar in nature due to slow rotation speeds resulting from stellar tidal effects. The field strengths were predicted to have values of 0.06–0.23 G for Proxima b, and 0.07–0.14 G for Ross-128 b. If either planet contains more than 10 per cent of their mass in volatiles, magnetic fields would either be non-existent or very weak. The conditions of both planets may be hostile for habitability.