Five Years of Mini-EUSO Observations from the ISS: Summary of Key Results

TL;DR

Mini-EUSO, operating on the ISS for five years, has provided valuable data on Earth's UV emissions, lightning, meteors, and transient phenomena, advancing space-based cosmic ray and atmospheric research.

Contribution

This paper summarizes five years of Mini-EUSO observations, highlighting its novel detection of meteors, elves, and UV emission maps, and demonstrating its capabilities for studying extreme cosmic and atmospheric phenomena.

Findings

Detected over 22,000 meteors, including three interstellar candidates.

Produced the first global UV emission maps of Earth.

Successfully identified and characterized elves and other TLEs.

Abstract

Mini-EUSO is the first space-borne detector of the JEM-EUSO (Joint Exploratory Missions for Extreme Universe Space Observatory) program, operating on the International Space Station (ISS) since October 2019. Designed to search for Ultra-High Energy Cosmic Rays (UHECRs) above 10$^{21}~$eV and capable of placing a stringent upper limit on their flux at these extreme energies, paving the way to future space-based UHECR observatories, Mini-EUSO has completed more than 150 observation sessions over five years, accumulating approximately 750 hours of data. The mission has produced the first global UV emission maps of Earth and provided valuable insights into lightning phenomena and Transient Luminous Events (TLEs), such as elves, as well as artificial light sources and meteors. Notably, Mini-EUSO has conducted the first systematic space-based meteor survey, detecting over 22,000 meteors and identifying three interstellar candidates. Among the observed TLEs, the most interesting class of phenomena are elves, which appear as expanding ring-shaped structures occurring at $\sim$90 km altitude. Mini-EUSO has detected elves with varying structures and different numbers of concentric rings, from single-ring up to five rings. Thanks to its imaging capabilities, fast time resolution, and favorable observational geometry, Mini-EUSO is uniquely suited to studying this kind of lightning phenomena, providing unprecedented insight into their dynamics. Additionally, the instrument has demonstrated the capability of a space-based detector to identify short light transients resembling extensive air shower signals while distinguishing them from those produced by UHECRs. This contribution presents a comprehensive summary of the Mini-EUSO mission, its status, and main results.