The summit of Alba Mons at center is encircled by the sweeping fracture systems of Tantalus Fossae to the east (right) and Alba Fossae to the west in this mosaic of images taken by NASA’s Viking orbiters in the late 1970s. Researchers think hydrogen chloride gas recently detected nearby may be seeping from magma below. Credit: NASA/JPL/USGS

Something is leaking from the ground near one of Mars’ largest volcanoes, and scientists think it’s a sign that active magma is buried below.

In a study published Nov. 4 in Science Advances , researchers report detections of hydrogen chloride (HCl) gas within 6 miles (10 kilometers) of the planet’s surface near the volcano Alba Mons. Notably, the detections came during aphelion, when Mars is farthest from the Sun and HCl is typically absent from its atmosphere.…