Evidence of ancient life on Mars may be hidden in colossal caves carved by water

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Vast “karst” caves may have been identified on Mars, formed when slightly acidic water dissolved bedrock, and are considered one of the best places on the Red Planet to search for preserved biosignatures.

“Given the expected technological advances in the coming decades, we believe that in situ exploration will be possible if missions are designed specifically for these goals Karst caves of Mars is an achievable goal,” said Chunyu Ding of the Institute for Advanced Study at Shenzhen University in China in an interview with Space.com.

The caves in the Hebrus Valles region between the extinct volcano Elysium and Mons Utopia Planitia In MarsIn the northern mid-latitudes, eight skylights become visible, which are holes in the ceiling of the caves, visible on the surface as pits ranging from tens to over 100 meters in diameter. The skylights differ from craters in that they do not have raised walls or splashes of ejecta around them. The skylights are believed to form when the surface partially collapses into the empty cavern below.

Caves and skylights have been found on Mars before, but when lava tubes formed within them Volcanic regions. Hebrus Valles, on the other hand, is not a volcanic region; It shows ancient river channels and abundant hydrated minerals and sediments deposited by them liquid waters on the surface a long time ago.

These features were identified by scientists led by Ding and his Shenzen colleague Ravi Sharma. Her team used archival data from various Mars missions, including mineralogical maps based on observations from NASA’s Thermal Emission Spectrometer on now-defunct Mars Mars Global SurveyorEvidence of hydrogen (as a proxy for water) from the Gamma radiation Spectrometer at the agency Mars Odysseyand models of the Martian terrain based on data from NASA’s HiRISE camera Mars reconnaissance orbiter.

They found that the skylights and their surroundings are consistent with so-called “karst caves.” Karst is the dissolution of bedrock containing carbonates and sulfates. While we find karst caves in many places EarthThis is the first time they have been identified on Mars.

The observations show that the Hebrus Valles region is rich in carbonate rocks such as limestone and sulfate rocks such as gypsum. Over 3.5 billion years ago when Mars was warmer and wetterThese carbonate and sulfate sediments were deposited by large basins of liquid water such as lakes and seas. As Mars cooled, the surface water disappeared and much of it formed subsurface ice and frozen brine.

In fact, data from Mars Odyssey’s gamma-ray spectrometer suggests that some water ice may still be present there. At some point, local warming events, perhaps from distant volcanoes, impacts, or long-term orbital fluctuations, would have melted the ice and brine beneath the surface, and the liquid water would have flowed through cracks and fractures in the ground, dissolving the rock and turning those cracks into large caves.

Not all regions of Mars meet the requirements for the formation of karst caves, since, on the one hand, carbonate and sulfate rocks are not omnipresent. Also, not all locations, particularly areas at lower latitudes, harbor subterranean ice and frozen brine or have been geologically stable long enough to allow the caves to form and their rocky ceiling to collapse and the skylights to form.

“Our results suggest that Hebrus Valles is probably not a completely isolated case, but these caves will not be everywhere on Mars either,” Ding said. “They are likely concentrated in a limited number of regions that meet the necessary depositional and hydrological conditions. It is quite reasonable to expect that additional karst caves will be discovered in other, similar environments in the future.”

In fact, there may be more to Hebrus Valles than just the eight caves; There may be others who have not yet experienced the ceiling collapse and will reveal themselves. The skylights known so far appear to have a diameter of several dozen to over 100 meters, and underground the cavities could be many times larger and several dozen meters deep.

Karst caves are the perfect place for shelter old biosignatures. The watery and stable microclimate in the caves could have harbored microbial colonies long ago, and today the caves are protected from the extreme conditions found on the surface of Mars, such as: B. widely varying daytime temperatures, dust storms and ultraviolet sunlight cosmic rays Radiation. Thus future life-seeking missions might try to research them.

However, the surrounding rock will limit the transmission of radio signals from inside the caves to orbiting spacecraft, making exploration of the caves more difficult but not impossible, Ding said.

“From a technical perspective, direct access to these caves is a major challenge,” he said. “However, our geomorphological analysis suggests that not all possible caves are simple vertical shafts. In our work we use the term ‘accessible potential karst caves’.”

Most skylights are characterized by steep walls that lead down into the darkness of the caves. However, in the eight caves of Hebrus Valles there is evidence of slopes consisting of rocky rubble in several step-like formations that could allow a gradual descent.

This could be achieved by multiple robotic explorers forming a communication chain into the caves, ranging from wheeled rovers carefully navigating down each step to climbing robots lowered using winches Air rotorcraft that can fly in and out of the skylights.

The cave’s rocky shielding may not only be suitable for preserving biosignatures, but could also provide protection for the future Mars astronautsto protect them and their outposts from the dangers of radiation and dust storms on the surface. If so, it could be that humanity’s future lies underground on Mars.

Ding’s team’s conclusions were published on October 30 The astrophysical diary letters.