NASA has selected a proposed solar mission for further study as part of its Small Explorer program, extending early design work rather than approving a launch. The mission, known as the Chromospheric Magnetism Explorer, or CMEx, will now move into an extended Phase A study lasting 12 months, with a budget of two million dollars. This phase allows scientists and engineers to refine the concept and test whether it is ready for future consideration. CMEx is designed to focus on the Sun’s chromosphere, a thin and restless layer above the visible surface. Researchers believe this region holds key clues to how solar eruptions begin and how the solar wind forms. The mission builds on earlier experimental work but remains at a study stage only.
NASA’s CMEx is meant to observe the Sun’s magnetic heart
CMEx is planned as a single spacecraft mission using ultraviolet spectropolarimetric instruments. These tools have already been tested during NASA’s CLASP sounding rocket flight, which briefly sampled the chromosphere during a sub orbital mission. CMEx would take this approach further by making steady, long-term observations rather than short snapshots. Its main goal is to measure magnetic fields in the lower chromosphere, something that has not yet been done continuously. Scientists see this layer as a link between the Sun’s surface and its outer atmosphere, where solar storms grow stronger and more complex.
Sun’s chromosphere matters
The chromosphere, a thin but vibrant layer, is located just above the photosphere, the one that we perceive from Earth. It is a very volatile layer that sometimes changes within minutes, so it is difficult to study it through short-period observations. Magnetic fields in this area behave like a living organism; they grow by twisting and stretching, and just look at them, switching to new shapes by breaking free from the old ones. Such a change could release previously hidden energy in the form of heat and particles traveling at high speeds. This occurrence may severely affect all sorts of events, such as solar flares or coronal mass ejections, which are large clouds of charged material ejected from the Sun and capable of reaching Earth. A careful observation of this layer might be a significant breakthrough for scientists in predicting the early signs of such eruptions.
CMEx could improve space weather tracking
Solar wind is a constant stream of charged particles flowing outward from the Sun. It plays a major role in space weather near Earth, affecting satellites, communication systems, and power grids. Scientists believe the magnetic roots of the solar wind lie partly in the chromosphere. By tracking how magnetic fields there connect to those further out in space, CMEx could fill a long-standing gap in understanding. NASA officials say that better knowledge of these processes could improve forecasts of harmful solar activity, helping protect both spacecraft and astronauts operating near Earth, the Moon, or Mars.
What happens next for the mission
The current Phase A extension does not guarantee that CMEx will fly. Instead, it gives the team time to refine the mission design, assess risks, and confirm costs. The study is led by Holly Gilbert of the National Center for Atmospheric Research in Boulder, Colorado. CMEx was originally proposed under the 2022 Heliophysics Explorers Program call, alongside other mission concepts. At the end of this extended study, NASA will decide whether the mission is ready to move forward. For now, CMEx remains a careful step toward seeing the Sun’s magnetic behavior more clearly, without rushing ahead.
