Should we rethink Mercury’s geologic history? A new study suggests the planet may have once had habitable conditions. This is evidenced by the presence of huge salt glaciers beneath its hostile surface.
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[EN VIDÉO] Mercury, the world of extremes. Very close to the sun, Mercury lives in hell, cooked at 400°C, where it shines…
When we talk about a planet that can or could have harbored life, Mercury seems to be completely out of the picture. Overheated by the Sun, from which it is only 46 million kilometers away, this small, dry and atmosphereless planet is actually very distant, providing the necessary conditions for the emergence of life.
At least on the surface. Because things could be very different in depth. This is suggested by a new study published in the Planetary Science Journal. New data that disrupts our understanding of the zone considered habitable in planetary systems and significantly expands the field of possibilities in astrobiology.
Salt glaciers release volatile elements
Due to its distance from the Sun, Mercury lies outside the habitable zone, which lies between Venus and Mars in our solar system. At more than 400°C in full sun there is no chance of finding liquid water. However, we now know that certain planets could offer favorable conditions for habitability despite extremely hostile surface environments. The hidden oceans of the icy moons of Jupiter and Saturn are perfect examples. But other than a huge iron core and a thin silicate shell, Mercury doesn’t hide an ocean of liquid water. So where might scientists have found conditions that could potentially support life?
Well, in glaciers… made of salt! While it was believed that Mercury’s crust was completely free of volatiles, this certainty was shattered by the passage of the Messenger probe between 2011 and 2015. In fact, sulfur, chlorine, sodium and potassium have been detected on the planet’s surface. Volatile elements appear to originate from underground, suggesting the presence of a “reservoir” hidden in the planet’s basement.
A more favorable environment for life in Mercury’s subsurface?
The new study also shows that these amounts of volatile elements could be much larger than previously thought. The results actually suggest that volatile element emanations are greater in areas with very chaotic terrain, with morphology reminiscent of Martian glaciers. Analysis of these areas, particularly at the poles, shows that they are large salt deposits that trapped volatile elements at the time of their formation. These very special glaciers, which were buried beneath Mercury’s subsurface for more than a billion years, would then have been exposed to the surface by asteroid impacts.
There are terrestrial analogues to this type of glacier, including the dry salt deposits of the Atacama Desert in Chile. However, we know that such environments can represent niches with favorable living conditions for extremophile organisms.
New perspectives in astrobiology
Based on modeling, the researchers suspect that these glaciers were formed during the collapse of a short-lived and warm primordial atmosphere early in Mercury’s history, before the Late Great Bombardment episode. The water in the atmosphere expelled by volcanic activity would thus have condensed on the surface during the long, cold nighttime periods that the planet experiences due to its slow rotation around itself. This scenario therefore suggests the temporary presence of shallow and very salty seas around 4 billion years ago. The subsequent rapid evaporation and loss of water into space would then have led to the formation of these huge salt deposits within the crust.
A new geological story that could give Mercury and its analogues elsewhere in the galaxy new appeal in the search for extraterrestrial life.