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Project Progress

The most comprehensive study of isotopic water in the atmosphere of Mars:
Villanueva et al. 2015, Science

We mapped atmospheric water (H₂O) and its deuterated form (HDO) on Mars, in four epochs. The maps reveal strong variations in isotopic enrichment (D/H) across the Martian globe and a high D/H enrichment in the near-polar regions, indicative of much greater water loss than previously inferred. Hemispheric maps that span seasons from late northern winter to late northern spring on Mars were acquired using high-resolution infrared spectroscopy. They sample the evolution of sublimation from the North polar cap, revealing that atmospheric water replenished during northern spring is seen with a representative value of D/H enriched by a factor of ~7 relative to Earth’s ocean (VSMOW). Certain basins and orographic depressions show even higher enrichment (8-10 VSMOW) while high altitude regions show much lower values (1-3 VSMOW). Part of this variability can be associated with Rayleigh distillation and/or cloud formation, yet such strong anisotropies are difficult to reconcile with current fractionation models. Our atmospheric maps indicate that water ice in the polar reservoirs is enriched in deuterium to at least 7.7 VSMOW, meaning that early Mars (4.5 Ga ago) had a global equivalent water layer at least 137 meters thick. The volume of Mars’ early ocean must have been at least 20 million km3, of which nearly 87% has escaped to space. By comparison, Earth’s Arctic Ocean holds 18.8 million km3 of water.

Based on the surface topology of Mars today, a likely location for this water would be in the Northern Plains, which has long been considered a good candidate because of the low-lying ground. An ancient ocean there would have covered 20% of the planet’s surface – by comparison, the Atlantic Ocean occupies 17% of Earth’s surface.

Building an extensive taxonomy for comets based on their volatile compositions:
We also published six papers on cometary science based on data acquired at infrared and millimeter wavelengths, emphasizing their composition based on primary volatiles: H₂O, CH₃OH, C₂H₆, NH₃, HCN, HC₃N, CO, etc. We extended our emerging compositional taxonomy for comets to additional bodies from the Jupiter Family (103P/Hartley 2) and Oort Cloud reservoirs (C/2009 P1 (Garradd), C/2012 F6 (Lemmon), C/2012 S1 (ISON), and C/2013 R1 (Lovejoy)). See GCA reports by B. Bonev, M. A. DiSanti, and L. Paganini.

We pioneered the use of the Atacama Large Millimeter (and sub-millimeter) Array (ALMA) for planetary and cometary science. Our papers on comets ISON and Lemmon describe the first cometary results to be acquired with ALMA. Our Titan paper is the first planetary paper to be published using ALMA data. See GCA report by S. Charnley.