The Probe of Extreme Multi-Messenger Astrophysics (POEMMA)*

The Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) was designed as a NASA Astrophysics probe-class mission to identify the sources of ultrahigh energy cosmic rays (UHECRs) and observe cosmic neutrinos from extremely energetic transient sources. POEMMA consists of two identical spacecraft flying in a loose formation at 525 km altitude oriented to observe a common atmospheric volume and to provide full-sky coverage for both types of messengers. Each spacecraft hosts a wide field of view Schmidt telescope with a hybrid focal plane optimized to observe both the UV fluorescence signal from extensive air showers (EASs) and the optical Cherenkov signals from EASs. When in stereo close to nadir mode, POEMMA can measure the spectrum, composition, and full-sky distribution of the UHECRs above 20 EeV and be sensitive to UHE neutrinos. When pointing just below the Earth’s limb, POEMMA will be sensitive to cosmic tau neutrinos above 20 PeV by observing the Cherenkov radiation of EASs produced by upward-moving tau decays, induced from tau neutrino interactions in the Earth. POEMMA is designed to quickly re-orient to follow a Target-of-Opportunity (ToO) neutrino transient from astrophysical sources with exceptional sensitivity to neutrinos from both short-duration transients, such as short-gamma-ray bursts (sGRBs), and long-duration sources, such as binary neutron star (BNS) mergers. Here we review the POEMMA mission and discuss the recent progress towards its technical readiness provided by the Mini-EUSO, EUSO-SPB1, and EUSO-SPB2 and the forthcoming Terzina and POEMMA-Balloon with Radio (PBR) missions.