# Kepler-730: A hot Jupiter system with a close-in, transiting, Earth-sized planet

## TL;DR

Kepler-730 is a unique planetary system with a hot Jupiter and a close-in, Earth-sized transiting planet, validated through combined spectroscopic and statistical methods, highlighting a rare system architecture.

## Contribution

This study presents the first validation of an Earth-sized planet in a system with a hot Jupiter, using spectroscopic data and false positive analysis.

## Key findings

- Validated the Earth-sized planet using radial velocities and statistical methods.
- Measured radii of the planets: approximately 1.57 Earth radii for the small planet.
- Kepler-730 is only the second known system with a hot Jupiter and an inner transiting planet.

## Abstract

Kepler-730 is a planetary system hosting a statistically validated hot Jupiter in a 6.49-day orbit and an additional transiting candidate in a 2.85-day orbit. We use spectroscopic radial velocities from the APOGEE-2N instrument, Robo-AO contrast curves, and Gaia distance estimates to statistically validate the planetary nature of the additional Earth-sized candidate. We perform astrophysical false positive probability calculations for the candidate using the available Kepler data and bolster the statistical validation by using radial velocity data to exclude a family of possible binary star solutions. Using a radius estimate for the primary star derived from stellar models, we compute radii of $1.100^{+0.047}_{-0.050}\ R_{Jup}$ and $0.140\pm0.012\ R_{Jup}$ ($1.57\pm0.13\ R_{\oplus}$) for Kepler-730b and Kepler-730c, respectively. Kepler-730 is only the second compact system hosting a hot Jupiter with an inner, transiting planet.