A Narrowband Technosignature Search Toward the Hycean Candidate K2-18b Using the VLA and MeerKAT

TL;DR

This work targets a search for narrowband technosignatures from the Hycean-planet candidate K2-18b using interferometric radio observations. A coordinated, multi-epoch campaign with the VLA and MeerKAT covers 544 MHz to 9.8 GHz and employs a robust post-processing pipeline to suppress RFI and Doppler-drift signals. No technosignatures are detected, establishing upper limits on persistent, isotropic transmitters of $10^{12}$ to $10^{13}$ W and delivering the first interferometric constraints for a Hycean candidate. The study demonstrates the viability of multi-epoch interferometric technosignature searches and provides a scalable framework for future observations of nearby potentially habitable exoplanets.

Abstract

K2-18b, a sub-Neptune exoplanet located in the habitable zone of its host star, has emerged as an important target for atmospheric characterization and assessments of potential habitability. Motivated by recent interpretations of JWST observations suggesting a hydrogen-rich atmosphere consistent with Hycean-world scenarios, we conducted a coordinated, multi-epoch search for narrowband radio technosignatures using the Karl G. Jansky Very Large Array equipped with the COSMIC backend and the MeerKAT telescope with the BLUSE backend. Our observations span frequencies from 544MHz to 9.8GHz and include multiple epochs that cover at least one full orbital period of the planet. In this work, we outline, create, and apply a comprehensive post-processing framework that incorporates observatory-informed RFI masking, drift-rate filtering based on the expected dynamics of the K2-18 system, multibeam spatial discrimination, primary and secondary transit filtering (when applicable), and SNR-based excision of weak and strong spurious signals. Across all bands and epochs, no signals consistent with an astrophysical or artificial origin were identified at a limit of 10^12 to 10^13W. These non-detections allow us to place upper limits on the presence of persistent, isotropic narrowband transmitters within the K2-18 system, providing the first interferometric technosignature constraints for a Hycean-planet candidate. Our results demonstrate the efficacy of coordinated multiepoch interferometric searches and establish a methodological framework for future technosignature studies of nearby potentially habitable exoplanets.