Placing the Solar System in its Astrophysical Context

TL;DR

This study compares the Sun and Solar System to other stars and exoplanetary systems using large astronomical surveys, revealing the Sun's modest anomalies and contextualizing its properties within the galaxy.

Contribution

It provides a comprehensive statistical analysis of the Sun's properties relative to similar stars, highlighting its unique features and placing the Solar System in an astrophysical context.

Findings

The Sun is modestly metal-rich compared to nearby stars.

The Sun has low photometric variability and specific elemental abundance patterns.

The Solar System lacks super-Earths and has low planetary eccentricities.

Abstract

We examine recent astronomical data to assess whether the sun and Solar System possess anomalous properties compared to other stars and exoplanetary systems, providing context for astrobiology research. Utilising data primarily from large surveys like {\it Gaia}, {\it Kepler}, {\it TESS}, and ground-based spectroscopy (e.g., GALAH, LAMOST, HARPS), we construct comparison samples (e.g., nearby stars, solar analogues and twins within 20-200 pc) and employ statistical methods, including regression analysis, to account for parameter dependencies. We find that the sun is modestly metal-rich compared to nearby solar-age stars. More anomalous solar properties include its mass (top $\sim$8 percent locally), low photometric variability on short timescales ($\sim$0.2 percent), specific light and heavy element abundance patterns (high beryllium, low lithium, low carbon/oxygen and nitrogen/oxygen ratios, and low heavy neutron capture and refractory elements), slow rotation, and low superflare rate. The sun has average $\alpha$/iron, phosphorus/iron, and Ytterbium/iron abundance ratios. It also has average chromospheric activity as measured by R$^{\rm '}_{\rm HK}$(T$_{\rm eff}$), R$^{\rm +}_{\rm HK}$, and H$\alpha$ indices. The Solar System is unusual in its lack of super-Earths despite hosting a cold Jupiter ($\sim$3 percent), the low eccentricities of its planets (especially considering detectability, $<2$ percent), its large size scale for a multi-planet system ($\sim$6 percent), and potentially the sun's obliquity. The sun's galactic orbit is less eccentric and has lower vertical excursions than $\sim$95 percent of nearby solar analogues. Its current position is near perigalacticon and minimum distance from the Galactic plane, resulting in a higher local star density than 98.8 percent of randomly chosen times from $-0.5$ to $+0.5$ Gyrs.