Next month, NASA’s New Horizons mission plans to shut off two instruments that study the solar wind because of a lack of funding from the agency, mission scientists say. The move comes even as the spacecraft nears the outer edge of the Solar System, following a different route than its far-out predecessors, Voyager 1 and 2.

Shutting off these instruments “would be an incalculable loss,” says Gary Zank, a space physicist at the University of Alabama in Huntsville. Unlike the Voyager missions, New Horizons can directly measure “pickup ions,” neutral atoms from interstellar space that become charged inside the heliosphere and get swept up by the solar wind. These particles sap energy from the solar wind and play a role in what happens at the termination shock, where the supersonic solar wind abruptly slows.

New Horizons is currently 66 times farther from the Sun than Earth and twice as far away as Pluto. It could cross the termination shock in the next few years. The spacecraft is in perfect health and could operate until 2050, Stern says. Such longevity would allow it to eventually cross the heliopause into interstellar space, enabling insights into how that boundary—which marks the edge of the Sun’s bubble—can shrink and grow over time, says James Green, NASA’s former chief scientist, who organized a petition to keep the instruments running. “This is a unique opportunity that we’re not going to get very often.”

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