CODEX

CODEX was a solar coronagraph installed on the International Space Station to gather information about the solar wind and how it forms. A coronagraph blocks out the bright light from the Sun to better see details in the Sun's outer atmosphere, or corona. CODEX was a collaboration between NASA Goddard Space Flight Center and the Korea Astronomy and Space Science Institute (KASI) with additional contribution from Italy's National Institute for Astrophysics (INAF). Its operations ended in September 2025.

CODEX had two key goals:

1. To understand what heats the solar wind to a million degrees hotter than the Sun’s surface and sends it streaming out at almost a million miles per hour.
2. To test models that show this heating and acceleration region.

CODEX was designed to help scientists understand the heating and acceleration of the solar wind, the constant stream of particles and magnetic fields that flow off of the Sun. While traditional coronagraphs look at the density of the solar wind in this area, CODEX observed the temperature and velocity of the solar wind in addition to the density. This information was to provide new insight to enable researchers to better understand where the energy that affects the solar wind comes from.

The coronagraph built upon research from other missions, such as Parker Solar Probe. CODEX looked at the solar wind much closer to the solar surface, as Parker Solar Probe sampled it a little farther out. Comparing these findings help scientists better understand the full picture of that region and how the solar wind changes as it travels farther from the Sun.

Scientists can also compare results with spacecraft that have solar coronagraphs, too, like the ESA (European Space Agency) and NASA Solar Orbiter mission and NASA’s Polarimeter to Unify the Corona and Heliosphere (PUNCH) mission.