A Terrestrial Planet in a ~1 AU Orbit Around One Member of a ~15 AU Binary

TL;DR

This paper reports the detection of a low-mass terrestrial planet around a star in a binary system using gravitational microlensing, highlighting the potential for discovering similar planets and informing models of planet formation.

Contribution

First detection of a terrestrial planet in a binary system via microlensing, demonstrating the method's effectiveness and suggesting increased sensitivity with current strategies.

Findings

Planet has 2 Earth masses and is located at ~0.8 AU from its host.

Host star is very low mass, less luminous than the Sun.

System's configuration suggests such planets are common.

Abstract

We detect a cold, terrestrial planet in a binary-star system using gravitational microlensing. The planet has low mass (2 Earth masses) and lies projected at $a_{\perp,ph}$ ~ 0.8 astronomical units (AU) from its host star, similar to the Earth-Sun distance. However, the planet temperature is much lower, T<60 Kelvin, because the host star is only 0.10--0.15 solar masses and therefore more than 400 times less luminous than the Sun. The host is itself orbiting a slightly more massive companion with projected separation $a_{\perp,ch}=$10--15 AU. Straightforward modification of current microlensing search strategies could increase their sensitivity to planets in binary systems. With more detections, such binary-star/planetary systems could place constraints on models of planet formation and evolution. This detection is consistent with such systems being very common.