By Meghan Bialt-DeCelie ’19

Since the discovery of perchlorates in soil acquired from Mars using the Pheonix Lander, researchers have been wondering how a liquid such as this can exist in the extreme cold temperatures found on the planet. A solution of perchlorate at 44% by weight can cause the freezing temperature of water to drop well below that of pure water. Researchers led by Samuel Lenton, PhD investigated the effects of a highly concentrated brine of magnesium perchlorate solution, which mimicked Martian water, on the structure of water molecules.

They were able to analyze the interactions and structure of the molecules of the Martian brine through EPSR computation modeling. EPSR simulations modeled the molecular structure and density of the atoms at the concentrations and temperatures experienced by the brine. The researchers found that the highly concentrated magnesium perchlorate solution caused a change in the spatial density of water causing its second coordination shell of electrons to completely combine with its first shell. This structure is similar to pure water being compressed under incredibly high pressure (2 GPa) resulting in the formation of level VII ice. They also found that the typical hydrogen bonds that take place between molecules of pure water are replaced with cation-water-anion bonds with the magnesium anions of the Martian mimic solution.

This gave researchers insight on the impact of highly concentrated salt solutions on water and how it causes enough change in the structure of water for it to remain in a liquid state in the extreme cold temperatures found on Mars. Exploring the difference in the structure of Martian water can expand our understanding of the limits of extraterrestrial life.

References:

1. S. Lenton, et al., Highly compressed water structure observed in a perchlorate aqueous solution. Nature Communications 8, (2017). doi: 10.1038/s41467-017-01039-9.
2. Image retrieved from: https://mars.nasa.gov/mer/gallery/press/spirit/20040119a.html