The Compton Spectrometer and Imager (COSI) will study gamma-ray emissions in the galaxy using a spacecraft in low Earth orbit. Credit: UC Berkeley

WASHINGTON — NASA will develop a gamma-ray telescope intended to study the formation of chemical elements in the galaxy as its next small astrophysics mission.

NASA announced Oct. 18 that it will proceed with development of the Compton Spectrometer and Imager (COSI) spacecraft as its next small Explorer, or SMEX, astrophysics mission. COSI, led by John Tomsick at the University of California Berkeley, is scheduled for launch in 2025.

COSI is designed to detect soft gamma rays, with intensities of between 0.2 and 5 million electron volts. Those measurements are designed to study gamma rays produced by the annihilation of positrons, the antimatter version of electrons, including why such emissions are concentrated around the center of the galaxy. It will also probe nucleosynthesis, or the formation of heavier elements, in supernova explosions.

“COSI will answer questions about the origin of the chemical elements in our own Milky Way galaxy, the very ingredients critical to the formation of Earth itself,” Thomas Zurbuchen, NASA associate administrator for science, said in a statement about the selection of the mission.

COSI was one of four finalists in the latest SMEX competition, winning funding in March 2020 for initial studies. One other finalist was a standalone mission, called the Extreme-ultraviolet Stellar Characterization for Atmospheric Physics and Evolution (ESCAPE), which would have looked for ultraviolet flares around nearby stars. The other two were “missions of opportunity”: a pair of smallsats called the Gravitational-wave Ultraviolet Counterpart Imager Mission and the LargE Area burst Polarimeter (LEAP), an instrument that would have been mounted on the International Space Station.

COSI leveraged experience the project team had flying a similar instrument on high-altitude balloons, most recently in 2016. For the upcoming mission, the instrument, called a Compton telescope, will be flown on a spacecraft in low Earth orbit.

The estimated cost of COSI is $145 million, excluding launch. NASA will select launch services for the mission at a later date.

NASA’s selection of COSI comes as the previous astrophysics SMEX mission nears launch. The Imaging X-ray Polarimetry Explorer (IXPE) satellite is set to launch Dec. 9 on a SpaceX Falcon 9 from Florida.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...