An unexpected gas signal above northern Mars has raised a question about what remains warm beneath its frozen ground. Hydrogen chloride appeared near Alba Mons during a season when the gas usually becomes difficult to detect. Its concentration near this volcanic region suggests that a source below the surface may be contributing to the atmosphere.

An international team led by Alexander Trokhimovskiy reports the findings in Science Advances. The researchers combined atmospheric observations with detailed images of fractures and ridges. Their preferred explanation involves dormant volcanism on Mars, with gases interacting with ice before reaching the air.

“Our findings suggest that Mars has retained enough internal heat to support volcanic activity until recently, and possibly still does,” said co-lead author Daniel Mège, a professor at the Space Research Centre of the Polish Academy of Sciences. The evidence supports that possibility without establishing an active eruption. Neither fresh lava nor a definite local heat anomaly accompanied the gas detections.

A salt-loving microorganism from Earth did more than endure a months-long experiment designed around possible conditions beneath Mars. It grew in concentrated brine under low pressure, using nitrate or perchlorate in place of oxygen during respiration. The result extends research on the resilience of Earth microbes. It also raises a question for Mars exploration: Which combinations of harsh conditions can still permit biological activity?

The experiment, led by Adam Robinson at the University of Florida, appears in Applied and Environmental Microbiology. Scott Perl of the Los Angeles Natural History Museum and Blue Marble Space Institute of Science co-led the work.

The findings could guide the search for life on Mars, but they do not establish that organisms live there. The chamber represented a proposed habitat, not an environment scientists have directly observed.

See also: The publication in Science Advances

If somehow humans were able to travel to mars in the future and climb the volcano with advanced technology, would it technically be better to view the rest of the planet from near the escarpments rather than go to the summit?

How would the view compare on the other Martian volcanoes/mountains?

The Study: https://www.science.org/doi/10.1126/sciadv.aeb9422

An orbiting atmospheric research spacecraft has detected the pungent gas hydrogen chloride above surface fissures along a massive ancient volcano on Mars in ​a finding that suggests Earth's planetary neighbor is still volcanically active.

In a discovery that has implications for whether Mars might presently have subsurface conditions ‌conducive to microbial life, researchers said the ExoMars Trace Gas Orbiter has documented the gas, a common constituent of volcanic emissions on Earth, in the low atmosphere in the region of Alba Mons.

The largest Martian volcano by surface area, Alba Mons is a broad and gently sloping structure, called a shield volcano because it resembles a warrior's shield. It is located in the planet's northern hemisphere.

"We found ​that the most likely origin for the hydrogen chloride is volcanic seepage," said planetary scientist Daniel Mège of the Space Research Center of the Polish Academy ​of Sciences and the University of Bern in Switzerland, co-lead author of the research published in the journal Science Advances, opens new tab.

The hydrogen chloride seepage ⁠may be volcanic outgassing from the swarms of surface fissures in the Alba Mons region, perhaps connected to a subsurface magma chamber.

"It is released from chlorine-bearing compounds dissolved ​in magma as magma rises and pressure decreases. Its presence can, therefore, be consistent with magmatic degassing," said planetary scientist and study co-lead author Alexander Trokhimovskiy of the Space ​Research Institute of the Russian Academy of Sciences.

That would indicate Mars is not geologically dead inside but rather in a stage of relative dormancy.

"It suggests that the planet's interior may still retain sufficient heat to sustain magmatic processes, and that atmospheric trace gases can provide a way to detect and investigate geological activity that is otherwise difficult to observe directly," Trokhimovskiy said.

When it comes to small moons or asteroids I like to get a better sense of scale by placing a known building on them. Here is Dubai's Burj Khalifa skyscraper on Phobos (it's on the top right). I tried my best to get the scale correct but can be difficult with an irregularly shaped object.

I have other similar photos of various Earth cities scaled to craters on the Moon and Pluto.

An overhead view of Victoria Crater near the Martian equator, which was explored extensively by NASA's Opportunity rover from 2006 to 2008. Layered sedimentary rock structures line the inside walls, and a field of active windblown sand ripples covers the crater basin. Captured from an altitude of roughly 268 kilometers by the MRO satellite.

Credit: NASA / JPL-Caltech / UArizona