KMT-2019-BLG-0842Lb: A Cold Planet Below the Uranus/Sun Mass Ratio

TL;DR

This paper reports the discovery of a cold exoplanet with a mass ratio similar to Uranus relative to the Sun, highlighting the importance of follow-up observations for detecting low-mass-ratio planets.

Contribution

It presents the detection and characterization of a cold planet with an extremely low mass ratio, comparable to Uranus/Sun, and discusses observational strategies for such low-mass-ratio planets.

Findings

The planet has a mass ratio of approximately 4.09e-5.

Estimated host star mass is about 0.76 solar masses.

The planet's mass is roughly 10.3 Earth masses.

Abstract

We report the discovery of a cold planet with a very low planet/host mass ratio of $q=(4.09\pm0.27) \times 10^{-5}$, which is similar to the ratio of Uranus/Sun ($q=4.37 \times 10^{-5}$) in the Solar system. The Bayesian estimates for the host mass, planet mass, system distance, and planet-host projected separation are $M_{\rm host}=0.76\pm 0.40 M_\odot$, $M_{\rm planet}=10.3\pm 5.5 M_\oplus$, $D_{\rm L} = 3.3\pm1.3\,{\rm kpc}$, and $a_\perp = 3.3\pm 1.4\,{\rm au}$, respectively. The consistency of the color and brightness expected from the estimated lens mass and distance with those of the blend suggests the possibility that the most blended light comes from the planet host, and this hypothesis can be established if high resolution images are taken during the next (2020) bulge season. We discuss the importance of conducting optimized photometry and aggressive follow-up observations for moderately or very high magnification events to maximize the detection rate of planets with very low mass ratios.