Thorium in solar twins: implications for habitability in rocky planets

Abstract

We have investigated the thorium (Th) abundance in a sample of 53 thin disc solar twins covering a wide range of ages. These data provide constrains on the mantle energy budget of terrestrial planets that can be formed over the evolution of the Galaxy's thin disc. We have estimated Th abundances with an average precision of 0.025 dex (in both [Th/H] and [Th/Fe]) through comprehensive spectral synthesis of a Th II line present at 4019.1290Å, using very high resolution (R = 115,000) high quality HARPS spectra obtained at the ESO La Silla Observatory. We have confirmed that there is a large energy budget from Th decay for maintaining mantle convection inside potential rocky planets around solar twins, from the Galactic thin disc formation until now, because the pristine [Th/H] ZAMS is super-solar on average under a uniform dispersion of 0.056 dex (varying from +0.037 up to +0.138 dex based on linear fits against isochrone stellar age). Comparing to neodymium (Nd) and europium (Eu), two others neutron-capture elements, the stellar pristine abundance of Th follows Eu along the Galactic thin disc evolution, but it does not follow Nd, probably because neodymium has a significant contribution from the s-process (about 60 per cent).

Carbon, isotopic ratio 12C/13C, and nitrogen in solar twins: constraints for the chemical evolution of the local disc

“…The sample is composed of 67 solar twins, stars with atmospheric parameters very similar to the Sun, within around ±100 K in T eff and ±0.1 dex in log g and [Fe/H] (Ramírez, Meléndez & Asplund 2009), studied previously by Bedell et al (2018), Spina et al (2018), and Botelho et al (2019. The atmospheric parameters are those by Spina et al (2018).…”

“…In the current work we have homogeneously measured precise abundances of carbon and nitrogen plus the carbon main isotopic ratio 12 C/ 13 C, in a sample of well-studied solar twins, having distances up to 100 pc and spanning a wide range of ages since around the formation epoch of the Galaxy's thin disc until a few hundreds Myr ago (Bedell et al 2018;Spina et al 2018;Botelho et al 2019). The analysis of our results is focused on the distributions of a set of CNO abundance ratios as a function of the age and metallicity of these solar twins in order to provide unprecedented and self-consistent constraints for GCE modelling (e.g.…”

On the Habitable Lifetime of Terrestrial Worlds with High Radionuclide Abundances

“…Spectroscopic surveys of solar twins and analogs have shown that the solar abundance of thorium is a few times lower (< 3) than other stars in the sample (Unterborn et al 2015;Botelho et al 2019). Overall, some worlds will be characterized by elevated abundances of long-lived radionuclides (Lugaro et al 2018).…”

The influence of bulk composition on the long-term interior-atmosphere evolution of terrestrial exoplanets

“…Bulk composition and mantle mineralogy affect the transport and material properties of the mantle, such as density and viscosity (Takeda 1998;Yamazaki & Karato 2001), and melting behavior (Hirschmann 2000;Kiefer et al 2015). Additionally, the budget of radiogenic elements varies among stars (Frank et al 2014;Unterborn et al 2015;Botelho et al 2019) and determines the heat production in planetary mantles, which also moderates the style of interior convection.…”