NASA’s Coronal Diagnostic Experiment (CODEX) is ready to launch to the International Space Station to reveal new details about the solar wind including its origin and its evolution.

Launching in November 2024 aboard SpaceX’s 31st commercial resupply services mission, CODEX will be robotically installed on the exterior of the space station. As a solar coronagraph, CODEX will block out the bright light from the Sun’s surface to better see details in the Sun’s outer atmosphere, or corona.

“The CODEX instrument is a new generation solar coronagraph,” said Jeffrey Newmark, principal investigator for the instrument and scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “It has a dual use — it’s both a technology demonstration and will conduct science.”

This coronagraph is different from prior coronagraphs that NASA has used because it has special filters that can provide details of the temperature and speed of the solar wind. Typically, a solar coronagraph captures images of the density of the plasma flowing away from the Sun. By combining the temperature and speed of the solar wind with the traditional density measurement, CODEX can give scientists a fuller picture of the wind itself.

“This isn’t just a snapshot,” said Nicholeen Viall, co-investigator of CODEX and heliophysicist at NASA Goddard. “You’re going to get to see the evolution of structures in the solar wind, from when they form from the Sun’s corona until they flow outwards and become the solar wind.”

The CODEX instrument will give scientists more information to understand what heats the solar wind to around 1.8 million degrees Fahrenheit — around 175 times hotter than the Sun’s surface — and sends it streaming out from the Sun at almost a million miles per hour.

This launch is just the latest step in a long history for the instrument. In the early 2000s and in August 2017, NASA scientists ran ground-based experiments similar to CODEX during total solar eclipses. A coronagraph mimics what happens during a total solar eclipse, so this naturally occurring phenomena provided a good opportunity to test instruments that measure the temperature and speed of the solar wind.

In 2019, NASA scientists launched the Balloon-borne Investigation of Temperature and Speed of Electrons in the corona (BITSE) experiment. A balloon the size of a football field carried the CODEX prototype 22 miles above Earth’s surface, where the atmosphere is much thinner and the sky is dimmer than it is from the ground, enabling better observations. However, this region of Earth’s atmosphere is still brighter than outer space itself.

“We saw enough from BITSE to see that the technique worked, but not enough to achieve the long-term science objectives,” said Newmark.

Now, by installing CODEX on the space station, scientists will be able to view the Sun’s corona without fighting the brightness of Earth’s atmosphere. This is also a beneficial time for the instrument to launch because the Sun has reached its solar maximum phase, a period of high activity during its 11-year cycle.

“The types of solar wind that we get during solar maximum are different than some of the types of wind we get during solar minimum,” said Viall. “There are different coronal structures during this time that lead to different types of solar wind.”

This coronagraph will be looking at two types of solar wind. In one, the solar wind travels directly outward from our star, pulling the magnetic field from the Sun into the heliosphere, the bubble that surrounds our solar system. The other type of solar wind forms from magnetic field lines that are initially closed, like a loop, but then open up.

These closed field lines contain hot, dense plasma. When the loops open, this hot plasma gets propelled into the solar wind. While these “blobs” of plasma are present throughout all of the solar cycle, scientists expect their location to change because of the magnetic complexity of the corona during solar maximum. The CODEX instrument is designed to see how hot these blobs are for the first time.

The coronagraph will also build upon research from ongoing space missions, such as the joint ESA (European Space Agency) and NASA mission Solar Orbiter, which also carries a coronagraph, and NASA’s Parker Solar Probe. For example, CODEX will look at the solar wind much closer to the solar surface, while Parker Solar Probe samples it a little farther out. Launching in 2025, NASA’s Polarimeter to Unify the Corona and Heliosphere (PUNCH) mission will make 3D observations of the Sun’s corona to learn how the mass and energy there become solar wind.

By comparing these findings, scientists can better understand how the solar wind is formed and how the solar wind changes as it travels farther from the Sun. This research advances our understanding of space weather, the conditions in space that may interact with Earth and spacecraft.

“Just like understanding hurricanes, you want to understand the atmosphere the storm is flowing through,” said Newmark. “CODEX’s observations will contribute to our understanding of the region that space weather travels through, helping improve predictions.”

The CODEX instrument is a collaboration between NASA’s Goddard Space Flight Center and the Korea Astronomy and Space Science Institute with additional contribution from Italy’s National Institute for Astrophysics.

By Abbey Interrante
NASA’s Goddard Space Flight Center, Greenbelt, Md.