Europe's Juice spacecraft was making a close pass by Earth on Monday, September 28, while a Swedish-built sensor began its first full scientific observations in space. The Swedish Institute of Space Physics said its Jovian Neutrals Analyzer, or JNA, had been switched on at full power after three years of planned inactivity. The European Space Agency scheduled the spacecraft's closest approach for 11:45 UTC over the Indian Ocean, at an altitude of about 8,640 kilometers.
Juice, short for Jupiter Icy Moons Explorer, launched in April 2023 on an eight-year journey to Jupiter. ESA designed the mission to examine the planet and the ocean-bearing moons Ganymede, Europa and Callisto. Its route uses encounters with the Moon, Venus and Earth to change direction and gain speed while preserving fuel for operations in the Jupiter system. The spacecraft previously passed the Moon and Earth in 2024 and Venus in 2025.
ESA projected that Monday's gravity assist would bend Juice's course by roughly 20 degrees and increase its speed by about 3.5 kilometers per second. During part of the approach, the probe crossed Earth's shadow and relied on battery power, requiring controllers to prioritize instrument activity. The agency had prepared opportunities for small course corrections before the encounter; those plans do not by themselves establish the flyby's final outcome.
The institute said JNA, developed in Kiruna, detects energetic neutral atoms that can reveal a planet's surrounding space environment from a distance. Engineers left it largely inactive so gases trapped in its materials could escape, reducing the risk of electrical discharges when its high-voltage system was engaged. A team gradually raised that voltage over 20 hours at ESA's control center in Darmstadt, Germany, during a July activation. Monday's Earth encounter gives the sensor its first chance to measure natural signals in space.
According to the institute, JNA is expected to observe the outermost reaches of Earth's atmosphere and nearby space. ESA said Juice's ten science instruments would gather Earth and Moon data between September 23 and October 3, helping teams calibrate equipment and analysis methods for Jupiter. The agency also planned observations in Earth's magnetic tail and images of the Moon's horizon to test optical navigation. Scientific results from these activities have yet to be assessed.
ESA plans another Earth flyby in January 2029 before Juice reaches Jupiter in July 2031. The mission is then due to investigate the giant planet's environment and its icy moons, with a later orbit around Ganymede planned for 2034. Researchers will examine the flyby measurements to determine how well the newly activated sensor performs before its principal work at Jupiter.
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