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Peroxy everywhere and what this means for Solid Body Exploration

Author: 
Friedemann Freund
Topic: 
Geochemistry/Petrology
Delivered As: 
Poster
Abstract Text: 

Peroxy may be one of the best-kept secrets when it comes to Solar System Solid Body Exploration. Peroxy are point defects that exist in the matrix of essentially all mineral grains and often along their surfaces. Peroxy are the products of a redox conversion that affects traces of dissolved “water” in minerals, which invariably enter the mineral matrix as “impurities” whenever minerals crystallize or condense in an H2O–laden environment. The redox conversion affects pairs of solute hydroxyls such as O3SiOH HOSiO3 changing them into peroxy, O3Si-OO-SiO3, plus H2. Since H2 are diffusively mobile, they are easily removed, leaving the peroxy behind. Peroxy defects are difficult to pin down. While all peroxy are subject to UV activation, those along grain boundaries easily break upon application of mechanical stress. The break-up generates electron–hole pairs, where the holes are defect electrons in the oxygen anion sublattice. Chemically equivalent to O– in a matrix of O2–, they are oxidizing radicals, •O, identical to the Reactive Oxygen Species (ROS), well known to biochemists. Thus, the presence of these highly reactive, highly oxidizing radicals in planetary surface materials, in particular dust and regolith, may have far-reaching consequences for human exploration of the moon and beyond.
Physically the O– behave as highly mobile electronic charge carriers, h•. They have the remarkable ability to flow out from the site where they have been generated, propagating fast and far. On the way the h• can interact with reduced transition metal cations such as Fe2+ oxidizing them to Fe3+. Unless temperatures are high, such oxidation reactions tend to be reversible. The h• preferentially trap at surfaces. If they encounter H2 molecules at grain surfaces, they can instantly “burn” H2 to H2O (verified at 300K). When the h• arrive at an interface with water ice, they are expected to oxidize H2O to H2O2, similar to the reaction demonstrated to take place at rock–liquid water interfaces. If h• encounter organics, they partially oxidize them to CO, or fully oxidize them to CO2, but partial oxidation to carboxylic acids and similar compounds also have to be considered.

Co-Authors: 
"Cesare Grava...
SSERVI Identifier: 
NESF2016-049

About SSERVI
Recognizing that science and human exploration are mutually enabling, NASA created the Solar System Exploration Research Virtual Institute (SSERVI) to address basic and applied scientific questions fundamental to understanding the Moon, Near Earth Asteroids, the Martian moons Phobos and Deimos, and the near space environments of these target bodies. As a virtual institute, SSERVI funds investigators at a broad range of domestic institutions, bringing them together along with international partners via virtual technology to enable new scientific efforts."