Unveiling the UHE Universe from space: the JEM-EUSO mission

The Extreme Universe Space Observatory onboard the Japanese Experiment Module (JEM-EUSO) is an international mission designed to explore the origin and nature of the of ultra high-energy cosmic rays (UHECR), with energies E>5.5x1019 eV, aiming at an integrated exposure of ∼106 km2 sr yr at E>1020 eV. Consisting of a near-UV 2.65 m diameter telescope with a field of view of 60o, JEM-EUSO looks down from space, monitoring the dark side of the Earth, to detect the fluorescence and Cherenkov light emitted along the linear track generated by a cosmic particle traversing the atmosphere. The energy and the arrival direction of each particle will be measured while the all 4π sky is monitored. The primary science goal of the mission is to identify the sources of the highest energy particles, and to measure their flux and spectrum, to unveil the mechanisms for the production, acceleration, and in situ propagation of these extreme particles. Other exploratory objectives of the mission include the study of the galactic and local extragalactic magnetic field; the detection of high-energy gamma rays and neutrinos, and tests of relativity and quantum gravity effects at extreme energies. Other aspects of fundamental physics that will be studied include the top-down models and the behavior of the neutrino cross sections at extreme energies. JEM-EUSO is also expected to conduct a systematic survey of the not yet well known energetic phenomena of the Earth's atmosphere. The mission is currently in the phase A study by JAXA and has been included in the ELIPS research pool of the European Space Agency. JEM-EUSO will be launched by an H2B rocket in the Japanese fiscal year 2016 and will be transferred to the ISS by an H2 Transfer Vehicle (HTV). It will be attached to the external experiment platform of the Japanese 'KIBO' module of the ISS. In this paper we summarize the science case, the science objectives, the technological and programmatic aspects of this challenging but fascinating mission.