- Most of the water on Mars is locked up as subsurface ice and in the rocks.
- Researchers discovered that Mars’ basalt rocks are capable to hold about 25% more water as compared to those on Earth.
- Approximately 9% excess volume of Martian mantle may include hydrous mineral species as a consequence of reactions in surface, compared to 4% volume of Earth’s mantle.
Nowadays, it’s not hard to tell thousands of scientists and engineers are studying the Red Planet. Although Martian surface looks frozen, barren, and uninhabitable, a trail of evidence shows that once it was a wetter and warmer planet where life may have thrived. No one exactly knows what happened to this excessive amount of water.
According the previous studies, a vast volume of water lost to space due to the collision of magnetic field of the planet. It might have locked up as subsurface ice or swept away by high intensity solar winds. However, these theories don’t shed light on where all of the Martian water has gone.
Two recent researches from the University of Oxford’s Department of Earth Sciences suggest that the water on Mars is now locked in the rocks. The surface of the Mars reacted with water and then absorbed it, which increased the process of rocks oxidation and made the planet unlivable.
How Did They Get To This?
The research team applied modeling techniques (used to examine the Earth’s rock composition) to measure how much water could be eliminated from the surface of the Mars through reactions with rock. They evaluated the role of subsurface pressure and rock temperature.
The team found out that Mars’ basalt rocks are capable to hold about 25% more water as compared to those on Earth, and therefore it absorbed the water from Martian surface into its interior.
There are numerous evidences that suggest that a different reaction is required to oxidize the Martian mantle. Let’s consider meteorites of Mars – they are chemically decreased compared to the rock’s surface, and in terms of composition, they look quite different. Mineralogy could be one of the many reasons for this.
The Plate tectonics of Earth prevent any major alterations in surface water levels, making wet rocks dehydrate before they enter the Earth’s dry mantle. Neither early Mars nor Earth had this recycling water system.
The water reacted with freshly erupted Martian lavas and it formed in a sponge-like effect. Then it reacted with Martian rocks to produce a wide range of water bearing minerals. This reaction completely changed the Martian rock mineralogy, causing the surface to dry and become uninhabitable.
Today’s Mars vs Mars 3.5 billion years ago | Image credit: Jon Wade
Now you might be wondering why the same never happened to Earth. The reason is Earth is much bigger than Mars with lesser iron content in its mantle rocks and different temperature profile, which affected in a significant way over time. The Martian surface is more prone to react with surface water and produce minerals containing water. These factors were some of the main reasons of Martian geological chemistry dragging water down into the mantle. On the other hand, the hydrated rocks on the Earth could float until they dehydrate.
Halogen Levels and Hydrospheric Water on Earth and Mars
A life could form and be sustainable if the halogen levels (including Bromine, Chlorine and Iodine) is appropriate. Too little or too much could cause sterilization.
Bromine (Br), Chlorine (Cl) and Iodine (I) are key tracers of accretionary processes owing to their incompatibility and high volatility, but most planetary materials and geological area have low abundances. However, neutron irradiation causes noble gas proxy isotopes that offer a high sensitivity tool for heavy halogen abidances.
A research team has used such isotopes to show that Br, Cl and I abundances in enstatite, carbonaceous, Rumuruti and primitive ordinary chondrites are nearly about 9 times, 6 times and 15 to 37 times lesser, respectively, than previous estimates.
According to the study, the halogen depletion of bulk silicate Earth relative to primitive meteorites is almost consistent with the lithophile elements’ depletion. Somewhere between 80 and 90% of heavy halogens are concentrated in the surface of Earth. Moreover, they have not experienced any serious early loss in atmosphere forming elements. The hydrophilic nature of halogen, whereby they track with water, is consistent with water-rich late state terrestrial accretion.
Reference: Nature | doi:10.1038/nature24625 | University of Oxford
Researchers have calculated the relative volumes of water that could be removed from Earth and Mars’s surface through burial and metamorphism of hydrated mafic (igneous rock rich in iron and magnesium) crusts. They analyzed mineral transition-induced bulk density changes at condition of elevated temperatures and pressure for each.
The calculations show that 9% excess volume of Martian mantle may include hydrous mineral species as a consequence of reactions in surface, compared to 4% volume of Earth’s mantle. This provided a crucial sink for hydrospheric water and an approach to oxidize the Martian mantle.
Reference: Nature | doi:10.1038/nature25031 | University of Oxford
The researchers are looking to test the effects of other sensitivities across the planets. What if Earth was smaller or bigger? What if Earth had less ore more iron in the mantle? The answers of these questions would help us better understand what is the exact role of rock chemistry in future fate of the planet.
Searching for life on other planets is not just about studying chemistry, but also very subtle things that might have a huge role in putting water on the surface. Most of these effects and their connections haven’t been explored yet.