JEM-EUSO
Joint Experiment Missions for
Extreme Universe Space Observatory

The origin and nature of Ultra-High Energy Cosmic Rays (UHECRs) remain unsolved in contemporary astroparticle physics. A cutoff in the cosmic ray energy spectrum clearly appears at ∼ 10²⁰ eV in the data of HIRES, Telescope Array and Auger on ground experiments. It is well known that the detection of events with energy ≥ 10²⁰eV is challenged by the GZK effect, which limits the highest detectable energy at ∼ 10²⁰ eV due to photopion production in the interaction of UHECR on the microwave fossil radiation of the Big Bang, as suggested also by the HIRES and Telescope Array data, or by nuclei photodisintegration as indicated by the Auger results. However, the possibility that the cutoff at  ∼ 10²⁰eV can be intrinsic to the acceleration power of the astrophysics cosmic ray sources remains alive. Moreover, indications of sources or excesses in the arrival direction distribution of UHECRs have been claimed by Telescope Array, in the Northern Hemisphere, and by Auger, in the Southern Hemisphere. To give an answer to these questions is rather challenging because of the extremely low flux of a few per km² per century at extreme energies such as E > 5 × 10¹⁹eV.

The objective of the JEM-EUSO program, Joint Exploratory Missions for Extreme Universe Space Observatory, is the realization of a space mission devoted to scientific research of cosmic rays of highest energies. Its super-wide-field telescope will look down from space onto the night sky to detect UV photons emitted from air showers generated by UHECRs in the atmosphere. 

About 300 researchers from 16 countries are collaborating in JEM-EUSO, with the support  of the most important International and National Space Agencies and research funding institutions.

Overview