# K2-288Bb: A Small Temperate Planet in a Low-mass Binary System Discovered by Citizen Scientists

## TL;DR

This paper reports the discovery and validation of a small, temperate exoplanet in a low-mass binary system, found through citizen science efforts using Kepler/K2 data, with implications for planet formation and habitability.

## Contribution

It presents the first validated small planet in a low-mass binary system discovered by citizen scientists, highlighting the role of public participation in exoplanet detection.

## Key findings

- The planet orbits the secondary star with a 31.39-day period.
- K2-288Bb has a radius of 1.9 Earth radii and is in or near the habitable zone.
- The system's architecture provides insights into planet formation in binary systems.

## Abstract

Observations from the Kepler and K2 missions have provided the astronomical community with unprecedented amounts of data to search for transiting exoplanets and other astrophysical phenomena. Here, we present K2-288, a low-mass binary system (M2.0 +/- 1.0; M3.0 +/- 1.0) hosting a small (Rp = 1.9 REarth), temperate (Teq = 226 K) planet observed in K2 Campaign 4. The candidate was first identified by citizen scientists using Exoplanet Explorers hosted on the Zooniverse platform. Follow-up observations and detailed analyses validate the planet and indicate that it likely orbits the secondary star on a 31.39-day period. This orbit places K2-288Bb in or near the habitable zone of its low-mass host star. K2-288Bb resides in a system with a unique architecture, as it orbits at >0.1 au from one component in a moderate separation binary (aproj approximately 55 au), and further follow-up may provide insight into its formation and evolution. Additionally, its estimated size straddles the observed gap in the planet radius distribution. Planets of this size occur less frequently and may be in a transient phase of radius evolution. K2-288 is the third transiting planet system identified by the Exoplanet Explorers program and its discovery exemplifies the value of citizen science in the era of Kepler, K2, and the Transiting Exoplanet Survey Satellite.