Hydrogen isotope evidence for loss of water from Mars through time

Abstract

The high D/H of the Martian atmosphere (∼5–6 × terrestrial) is considered strong evidence for the loss of Martian water to space. The timing and magnitude of the loss of water from Mars can be constrained by measurements of D/H in Martian meteorites. Previous studies of Martian meteorites have shown a large range in D/H, from terrestrial values to as high as the current Martian atmosphere. Here we show that the ancient (∼4 Ga) Mars meteorite ALH84001 has a D/H 4 × terrestrial and that the young (∼0.17 Ga) Shergotty meteorite has a D/H 5.6 × terrestrial. We also find that the young Los Angeles shergottite has zoning in D/H that can be correlated to igneous growth zoning, strongly suggesting assimilation of D‐enriched water during igneous crystallization near the Martian surface. In contrast to previous studies, we find higher and less variable D/H ratios in these three meteorites. Our results suggest a two‐stage evolution for Martian water—a significant early loss of water to space (prior to 3.9 Ga) followed by only modest loss to space in the last 4 billion years. The current Martian atmospheric D/H has remained essentially unchanged for the last 165 Ma.

Validity of the Apatite/Merrillite Relationship in Evaluating the Water Content in the Martian Mantle: Implications from Shergottite Northwest Africa (NWA) 2975

“…Some grains contain Cl amounts at the limit of detection (<50 ppm). Trace abundances of halogens in extra-terrestrial merrillites have been reported [6,12,50].…”

Juvenile chemical sediments and the long term persistence of water at the surface of Mars

“…If habitable environments did exist on early Mars, they are separated from Meridiani Planum and younger intervals by late heavy bombardment (Frey, 2008), the termination of the magnetic dynamo (Lillis et al, 2008), and associated atmospheric loss (Greenwood et al, 2008;Tian et al, 2009). Tian et al (2009) (Sleep et al, 1989), with one of the last very large impacts, recorded by the ~1350 km Isidis Basin, forming at ~3.8-3.9 Ga (Frey, 2008).…”

New measurements of D/H on Mars using EXES aboard SOFIA

“…Indeed, the main mechanism responsible for the deuterium enrichment in the Martian atmosphere is expected to be fractionation through differential escape rates of the D and H atoms, the post-decomposition products of the HDO and H 2 O molecules (Owen et al 1988). The disk-integrated estimate of the D/H ratio must be compared with its value in the past, measured in the most ancient SNC meteorites and/or in clays at the Martian surface (Greenwood et al 2008;Usui et al 2012;Mahaffy et al 2015). For a precise measurement of the present D/H ratio on Mars and in order to avoid any possible seasonal variation, D/H should be, as much as possible, integrated over an entire Martian year.…”