ESA's Proba-3 mission detects anomalously high slow solar wind speeds

Initial scientific data from the European Space Agency’s (ESA) Proba-3 mission is challenging existing models of solar wind formation. The primary conclusion of the study, published in The Astrophysical Journal Letters in March 2026, reveals that gusts of slow solar wind in the Sun's inner corona travel at speeds far exceeding theoretical expectations.

Launched in December 2024 aboard an ISRO PSLV-XL rocket, Proba-3 employs advanced precision formation flying to create artificial solar eclipses. This technique enables observations of the inner corona—an area usually hidden by the intense glare of the solar disk. Key ESA findings show that the slow solar wind, which was previously thought to move at roughly 100 kilometers per second near the Sun’s surface, was measured at speeds of up to 480 kilometers per second. These recorded velocities are three to four times higher than predicted, nearing the speeds typically associated with the fast solar wind.

Andrei Zhukov, a solar physicist at the Royal Observatory of Belgium and lead author of the study, confirmed that these plasma bursts were moving significantly faster than anticipated. Joe Zander, ESA's Proba-3 project scientist, noted that the initial data set has already yielded surprising results regarding solar wind speeds and accelerations near the Sun. The Proba-3 technology demonstrator consists of two satellites—the Coronagraph (CSC) and the Occulter (OSC)—which fly approximately 150 meters apart with millimeter-level precision. Since July 2025, the mission has simulated 57 artificial eclipses and recorded more than 250 hours of high-resolution video, the equivalent of roughly 5,000 ground-based observation campaigns.

The discrepancy between observed and expected wind speeds challenges current theories on coronal heating mechanisms, which appear to be more energetic than once thought. Solar wind speed is inextricably linked to the mystery of coronal heating, where temperatures soar to a million degrees Celsius. Faster-than-expected slow solar wind complicates the forecasting of space weather, which can disrupt power grids and satellite communications on Earth. Operating during the active phase of Solar Cycle 25, the Proba-3 mission addresses a critical gap in inner corona observations, complementing data from spacecraft such as NASA’s Parker Solar Probe and ESA’s Solar Orbiter.