PUNCH News

This beautiful, ghostly polarimetric rainbow reveals the direction and degree of polarization of the ghostly zodiacal light, in a preliminary data product from the WFI-2 spacecraft. On 18-April, WFI-2 executed its first polarimetric triplet imaging, collecting images through all three of its polarizers in succession. The polarimetric triplet image, expressed as RGB color channels, reveals the direction (via hue) and degree (via saturation) of polarization everywhere in the field of view all at once. WFI looks to one side of the Sun (marked with a star glyph). This image, made with Level 0 (uncalibrated) data direct from the WFI-2 camera, is consistent with existing results (Leinert et al. 1998) on the direction and degree of polarization of the zodiacal light. Stars appear white because they are mostly unpolarized compared to the 7% polarization of the zodiacal light. PUNCH uses a novel mathematical formalism (“MZP”, DeForest et al. 2022) to manipulate and background-subtract the polarimetric values from each of its four cameras. Chromatic treatment of coronal polarization was demonstrated at the 2023 total solar eclipse (Patel et al. 2023), highlighting the long-term synergy between ground- and space-based observations of the corona.

PUNCH opened the protective doors of its first two instruments, the Narrow Field Imager (NFI) and one of its three Wide Field Imagers (WFI-2) on 14-April. First-light images from WFI and NFI reveal that they are in focus, functioning nominally, and able to collect the deep field images needed for PUNCH science. The first image from WFI-2 is a spectacular view of approximately 40° of sky, including zodiacal light, several constellations, and various other astronomical objects. The first image from NFI reveals in-focus performance and resolution of the faint starfield close to the Sun. These two images are composited here to show how the instruments’ data will fit together once commissioning is finished.

During the week of 2025 April 7, PUNCH collected calibration data from the instruments – our last chance to take advantage of closed doors, before they open. Even these “dark frames”, taken with the doors closed, are interesting to look at. These images are “Level 0” (unprocessed) data products generated by the Science Operations Center (SOC), with full flight metadata attached. The cameras are working properly, with low noise levels. The images are brighter on the right because PUNCH uses dual readout detectors, with separate digitizers for the two halves of the images; they have slightly different zero points, an effect we remove at “Level 1” and higher. There is a very small amount of light visible in the upper left, which we believe is stray light scattered by the closed instrument door itself. Over the South Atlantic Anomaly in Earth’s magnetic field, an area of enhanced cosmic ray flux, we see significant particle impacts on the detector. The rate of impacts agrees with calculations performed over six years ago, during the mission’s Phase A concept study.

PUNCH will maintain the constellation with a novel, water-powered, shot-glass-sized rocket engine attached to each spacecraft. Each spacecraft carries about a British pint (600 g) of water in a small canister. To run the engine, PUNCH electrolyzes about 1/10 tsp (0.5 mL) of water, building up small stores of hydrogen and oxygen at about 200 psi. Then it burns the fuel in just a few seconds. Each cycle delivers a “kick” of about one inch/sec (2 cm/sec): just enough to correct for small orbital shifts and keep the constellation stable. PUNCH is the first space mission to use this type of engine, which carries safe propellant but is complex to operate.

On March 29, 2025, many folks went outside to catch a glimpse of the partially eclipsed Sun, as the Earth carried them through the Moon’s shadow. PUNCH, orbiting high overhead, also passed through the shadow. Orbital velocities are high, so each spacecraft passed through the darkest part of the partial eclipse (the Moon’s penumbra) at a slightly different time, about eight minutes apart. Even though the instruments’ doors are still closed for commissioning, PUNCH registered the eclipse. During the brief interval of darkest shadow, the solar arrays couldn’t keep up with on-board power usage and each spacecraft briefly switched to battery power, using slightly less than 1% of its battery capacity to keep operating normally through the brief gap.

While making its unique observations, PUNCH will augment a fleet of international spacecraft observing the Sun and solar system, including NASA's Parker Solar Probe and STEREO missions, the European Space Agency's (ESA) Solar Orbiter and Jupiter Icy Moon Explorer (JUICE) missions, and the ESA/Japanese Space Agency's (JAXA) BepiColombo mission, all of which afford unique joint science opportunities. The longitudinal trajectories of these missions are shown along with the orbits of Mercury, Venus, and Mars relative to an Earth-stationary frame of reference. On this scale, PUNCH is always located at Earth. Trajectories were generated by the Austrian Space Weather Office / GeoSphere Austria (Möstl/Davies/Weiler) – further details and additional movies available.

The Science Operations Center (SOC) for PUNCH received the first data packets from the four spacecraft. The data downlinks included both engineering and test image packets. The SOC successfully decompressed the packets and reconstructed the expected striped test pattern image. Using a test pattern allows the SOC to verify that data is properly transmitted and formed into images. The spacecraft sends engineering packets down alongside the images that indicate spacecraft parameters such as orientation and position. The SOC’s automated processing routines ingested this data and confirmed the spacecraft are pointing toward the Sun as expected. A good estimate of the spacecraft pointing is critical for the SOC’s data processing; it would not be possible to construct the seamless mosaics required to answer PUNCH’s science questions without it. The next step is to collect and process calibration images without light on the sensor, commonly called dark images. More information about the SOC processing can be found on GitHub.