Colloquium with T. Gregory Guzik, Director and Professor, Louisiana Space Grant / NASA EPSCoR Program, Department of Physics and Astronomy. 

Cosmic “rays” are atomic nuclei traveling at speeds close to the speed of light coming from outside our solar system. Since their discovery over 100 years ago much has been learned about these misnamed “rays”, but definitive evidence of their origin and acceleration to high energy remains elusive. The CALorimetric Electron Telescope (CALET), is a Japanese-Italian-US high-energy astroparticle physics experiment installed on the International Space Station (ISS) during 2015 that is providing new insight into this alien matter from outer space. In particular, the primary goals of the CALET mission include studying the details of galactic cosmic-rays including searching for possible nearby sources of high-energy electrons and dark matter signatures. CALET measures the cosmic-ray electron-plus-positron flux up to 20 TeV, gamma-rays to 10 TeV, and nuclei with Z=1 to 40 up to 1,000 TeV. Charge measurements cover the range from Z=1 to 40, enabling the study of individual elements and extending the range of long-term observations above iron. Gamma ray observations include the observation of high-energy gamma rays plus a search for electromagnetic counterparts for LIGO/Virgo gravitational wave events and gamma-ray bursts. Further, CALET also has the capability to monitor solar modulation effects and measure space weather events such as Relativistic Electron Precipitation (REP). Since the start of operations in mid-October, 2015, CALET has been in continuous observation mode for over 8 years without any major interruption. Every month approximately 20 million events with energies > 10 GeV are recorded. Here, we present a description of the CALET instrument and principle of operation, as well as highlights of the CALET results.  These include the electron + positron energy spectrum, the spectra of protons, helium and other nuclei, gamma-ray observations, some results on the electromagnetic counterpart search for LIGO/Virgo gravitational wave events, as well as solar modulation and REP observations. LSU is the lead institution of the U.S. CALET collaboration which includes NASA Goddard Space Flight Center and Washington University at St. Louis. Together this collaboration will submit in January 2024 a multi-million dollar proposal to NASA for continuing support and analysis of CALET measurements through the end of 2028.