A Martian Volcano Gets Bad Breath in Summer

Puffs of hydrogen chloride keep turning up over the northern slopes of Alba Mons, a Martian volcano thought to be asleep. The gas smells like vinegar spiked with heavy-duty toilet cleaner. And it only shows up in summer.

The sniffing was done by the European Space Agency's ExoMars Trace Gas Orbiter. Most of the gas it detects probably has a tidy weather explanation. Down south, summer warmth vaporizes ice and may free trapped gas, then autumn frost drags it back to the ground.

The north shouldn't play along. Mars' lopsided orbit puts northern summer far from the sun, so that ice cycle stays feeble there. Yet the orbiter logged sharp pulses in the north, clustered over one spot on Alba Mons.

Alba Mons rivals the Lower 48 U.S. states in area, and its lava flows look geologically young. Its northern flank holds a set of fissures, each roughly 330 feet (about 100 meters) long, which researchers link to vertical sheets of magma. On Earth, volcanoes can release hydrogen chloride when rising magma loses pressure. The team, writing in Science Advances, suggests molten rock below might be venting the gas, with winter ice capping the ground until summer.

They are clear it isn't proof. Nobody can say the gas comes from those exact fissures. Hot water reacting with metal chlorides could make it too, and NASA's InSight lander never picked up convincing magmatic tremors from the region.

If it is magma, Mars might still manage a rare eruption, and warm rock stirring hot water underground could make a hidden home for microbes.

Mars was supposed to have gone cold eons ago. Come northern summer, something on Alba Mons clears its throat anyway.

Read the full story at National Geographic, November 4, 2026

Hot Take: Alba Mons uses winter ice like a pot lid, then lifts it every summer to check on dinner. Whatever might be simmering under there, an orbiter caught the whiff from space.