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 \pm 1.0 ; M3.0 \pm 1.0 ) hosting a small ( R \textsubscript p = 1.9 R \textsubscript \Earth ) , temperate ( T \textsubscript eq = 226K ) 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 ( a _ { proj } \sim 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 identified by the Exoplanet Explorers program and its discovery exemplifies the value of citizen science in the era of Kepler , K2 , and TESS .