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The Earth is immersed in material streaming from the sun. This stream, called the solar wind, is washing over our planet, causing breathtaking auroras, impacting satellites and astronauts in space, and even affecting ground-based infrastructure.

NASA's PUNCH (Polarimeter to Unify the Corona and Heliosphere) mission will be the first to image the sun's corona, or outer atmosphere, and solar wind together to better understand the sun, solar wind, and Earth as a single connected system.

Launching no earlier than Feb. 28, 2025, aboard a SpaceX Falcon 9 rocket from Vandenberg Space Force Base in California, PUNCH will provide scientists with new information about how potentially disruptive solar events form and evolve. This could lead to more accurate predictions about the arrival of space weather events on Earth and the impact on humanity's robotic explorers in space.

"What we hope PUNCH will bring to humanity is the ability to really see, for the first time, where we live inside the solar wind itself," said Craig DeForest, principal investigator for PUNCH at Southwest Research Institute's solar system Science and Exploration Division in Boulder, Colorado.

Seeing solar wind in 3D

The PUNCH mission's four suitcase-sized satellites have overlapping fields of view that combine to cover a larger swath of sky than any previous mission focused on the corona and solar wind. The satellites will spread out in low Earth orbit to construct a global view of the solar corona and its transition to the solar wind. They will also track solar storms like coronal mass ejections (CMEs). Their sun-synchronous orbit will enable them to see the sun 24/7, with their view only occasionally blocked by Earth.

Typical camera images are two-dimensional, compressing the 3D subject into a flat plane and losing information. But PUNCH takes advantage of a property of light called polarization to reconstruct its images in 3D.

As the sun's light bounces off material in the corona and solar wind, it becomes polarized—meaning the light waves oscillate in a particular way that can be filtered, much like how polarized sunglasses filter out glare off of water or metal. Each PUNCH spacecraft is equipped with a polarimeter that uses three distinct polarizing filters to capture information about the direction that material is moving that would be lost in typical images.

"This new perspective will allow scientists to discern the exact trajectory and speed of coronal mass ejections as they move through the inner solar system," said DeForest. "This improves on current instruments in two ways: with three-dimensional imaging that lets us locate and track CMEs which are coming directly toward us; and with a broad field of view, which lets us track those CMEs all the way from the sun to Earth."

All four spacecraft are synchronized to serve as a single "virtual instrument" that spans the whole PUNCH constellation.

The PUNCH satellites include one Narrow Field Imager and three Wide Field Imagers. The Narrow Field Imager (NFI) is a coronagraph, which blocks out the bright light from the sun to better see details in the sun's corona, recreating what viewers on Earth see during a total solar eclipse when the moon blocks the face of the sun—a narrower view that sees the solar wind closer to the sun.

The Wide Field Imagers (WFI) are heliospheric imagers that view the very faint, outermost portion of the solar corona and the solar wind itself—giving a wide view of the solar wind as it spreads out into the solar system.

"I'm most excited to see the 'inbetweeny' activity in the solar wind," said Nicholeen Viall, PUNCH mission scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "This means not just the biggest structures, like CMEs, or the smallest interactions, but all the different types of solar wind structures that fill that in between area."

When these solar wind structures from the sun reach Earth's magnetic field, they can drive dynamics that affect Earth's radiation belts. To launch spacecraft through these belts, including ones that will carry astronauts to the moon and beyond, scientists need to understand the solar wind structure and changes in this region.

Building off other missions

"The PUNCH mission is built on the shoulders of giants," said Madhulika Guhathakurta, PUNCH program scientist at NASA Headquarters in Washington. "For decades, heliophysics missions have provided us with glimpses of the sun's corona and the solar wind, each offering critical yet partial views of our dynamic star's influence on the solar system."

When scientists combine data from PUNCH and NASA's Parker Solar Probe, which flies through the sun's corona, they will see both the big picture and the up-close details. Working together, Parker Solar Probe and PUNCH span a field of view from a little more than half a mile (1 kilometer) to over 160 million miles (about 260 million kilometers).

Additionally, the PUNCH team will combine their data with diverse observations from other missions, like NASA's CODEX (Coronal Diagnostic Experiment) technology demonstration, which views the corona even closer to the surface of the sun from its vantage point on the International Space Station.

PUNCH's data also complements observations from NASA's EZIE (Electrojet Zeeman Imaging Explorer)—targeted for launch in March 2025—which investigates the magnetic field perturbations associated with Earth's high-altitude auroras that PUNCH will also spot in its wide-field view.

As the solar wind that PUNCH will observe travels away from the sun and Earth, it will then be studied by the IMAP (Interstellar Mapping and Acceleration Probe) mission, which is targeting a launch in 2025.

"The PUNCH mission will bridge these perspectives, providing an unprecedented continuous view that connects the birthplace of the solar wind in the corona to its evolution across interplanetary space," said Guhathakurta.

The PUNCH mission is scheduled to conduct science for at least two years, following a 90-day commissioning period after launch. The mission is launching as a rideshare with the agency's next astrophysics observatory, SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer).

"PUNCH is the latest heliophysics addition to the NASA fleet that delivers groundbreaking science every second of every day," said Joe Westlake, heliophysics division director at NASA Headquarters in Washington. "Launching this mission as a rideshare bolsters its value to the nation by optimizing every pound of launch capacity to maximize the scientific return for the cost of a single launch."