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\t\t\t\t\t\t11\/12\/2025
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The European Space Agency\u2019s Swarm mission detected a large but temporary spike of high-energy protons at Earth\u2019s poles during a geomagnetic storm in November. It did this not with the scientific instruments for measuring Earth\u2019s magnetic field, but with its \u2018star tracker\u2019 positioning instruments \u2013 a first for the Swarm mission.<\/p>\n
While Swarm\u2019s magnetometers detected magnetic fluctuations 10 times stronger than normal on 12 November, it was the star trackers that detected a temporary increase in high-energy protons around the poles. During the geomagnetic storm of 11-13 November, levels of high-energy proton flux were 300 times higher than normal levels.<\/p>\n
\tMeasuring the magnetosphere<\/p>\n
\t\t\t\t\t\t\tHigh-energy proton flux in polar regions, by Swarm<\/a><\/p>\n Swarm<\/a>, an Earth Explorer mission developed under ESA\u2019s Earth Observation FutureEO programme<\/a>, is dedicated to understanding more about the invisible force field around our planet. Earth\u2019s magnetic field reaches from deep inside the planet\u2019s molten core and extends far out into space, protecting us from cosmic radiation and solar winds by deflecting harmful charged particles.<\/p>\n Orbiting at an altitude of 400\u2013500 km, the Swarm satellites are perfectly positioned to monitor the effects of geomagnetic storms.<\/p>\n Each of the three Swarm satellites, launched together in 2013, carries several instruments, including two types of magnetometer, which are able to measure both the strength and the direction of the magnetic field. They also carry star trackers to ensure correct location and orientation in space.<\/p>\n Star trackers are optical instruments that measure a satellite\u2019s position and attitude (orientation) by determining its position in relation to stars. So, while star trackers are normally used to correctly position satellites in space, in this instance Swarm\u2019s star trackers became a surprising source of important data.<\/p>\n \tThe November solar event<\/p>\n \t\t\t\t\t\t\tHigh-energy proton flux over the polar regions<\/a><\/p>\n Between 11-13 November 2025, Earth was hit by an exceptionally strong solar storm, caused by three consecutive coronal mass ejections within 48 hours.<\/p>\n These gave rise to \u2018proton auroras\u2019, which appear as a more diffuse light or glow in the sky and are typically seen at much lower latitudes during strong storms. Electron auroras, on the other hand, are associated with the appearance of \u2018ripples\u2019 of light in the sky and are often at higher latitudes.<\/p>\n While geomagnetic storms cause beautiful aurora, the charged particles emitted by the Sun\u2019s flares can pose a threat to infrastructure on Earth, with the potential to interrupt and damage energy grids and communications. On this occasion<\/a>, a short radio blackout was recorded across Europe, Africa and Asia, lasting approximately 30\u201360 minutes.<\/p>\n \tWhat Swarm saw: from stars to protons<\/p>\n \t\t\t\t\t\t\tAurora seen over Norway<\/a><\/p>\n On 12 November, the star trackers detected a huge influx of high-energy protons entering the polar regions. During severe geomagnetic storms, Earth\u2019s magnetic shield becomes disturbed, allowing a much greater number of energetic particles to reach low-Earth orbit \u2013 and in this case, the flux was unusually intense. This high-energy solar proton event is a rare phenomenon.<\/p>\n While they\u2019re not a danger to people on Earth, high-energy protons can severely disrupt and damage spacecraft electronics, including solar cells, and are hazardous to human spaceflight.<\/p>\n \u201cThis is a fascinating use of Swarm\u2019s star trackers, which are normally used to correctly orient the satellites,\u201d said ESA\u2019s Swarm Mission Manager, Anja Stromme. \u201cThe high-energy particle product is a newly implemented functionality for Swarm, and the products will be released operationally on 17 December. This is therefore the first event where a space weather event is monitored by Swarm\u2019s star trackers.\u201d<\/p>\n The star tracker image sensors are sensitive to high-energy protons. When one hits the sensor, it appears as a white spot on the image. While this is normally considered an inconvenience, the spots can also record the flux of energetic protons with energy higher than 100 MeV.<\/p>\n