Revising Properties of Planet-host Binary Systems II: Apparent Near-Earth Analog Planets in Binaries Are Often Sub-Neptunes

TL;DR

This study revises the properties of planets in binary systems hosting near-Earth analogs, revealing most are likely sub-Neptunes rather than rocky planets, which impacts the calculation of Earth-like planet occurrence rates.

Contribution

It provides revised stellar and planetary parameters for binary systems with near-Earth analogs, highlighting that most are sub-Neptunes and refining the criteria for rocky planet candidates.

Findings

10 of 17 planets are likely sub-Neptunes, above the radius gap.

Only 2 planets are potentially rocky and in the habitable zone.

Revised stellar parameters significantly affect planet classification.

Abstract

Identifying rocky planets in or near the habitable zones of their stars (near-Earth analogs) is one of the key motivations of many past and present planet-search missions. The census of near-Earth analogs is important because it informs calculations of the occurrence rate of Earth-like planets, which in turn feed into calculations of the yield of future missions to directly image other Earths. Only a small number of potential near-Earth analogs have been identified, meaning that each planet should be vetted carefully and then incorporated into the occurrence rate calculation. A number of putative near-Earth analogs have been identified within binary star systems. However, stellar multiplicity can bias measured planetary properties, meaning that apparent near-Earth analogs in close binaries may have different radii or instellations than initially measured. We simultaneously fit unresolved optical spectroscopy, optical speckle and near-infrared AO contrasts, and unresolved photometry, and retrieved revised stellar temperatures and radii for a sample of 11 binary Kepler targets that host at least one near-Earth analog planet, for a total of 17 planet candidates. We found that 10 of the 17 planets in our sample had radii that fell in or above the radius gap, suggesting that they are not rocky planets. Only 2 planets retained super-Earth radii and stayed in the habitable zone, making them good candidates for inclusion in rocky planet occurrence rate calculations.