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2014 Annual Science Report

NASA Goddard Space Flight Center Reporting  |  SEP 2013 – DEC 2014

Remote Sensing of Organic Volatiles on Mars and Modeling of Cometary Atmospheres

Project Summary

During this period, Dr. Villanueva mainly worked on processing high-resolution (spectral and spatial) data of Mars acquired in January/2014 and in the observational campaigns of 2008, 2009 and 2010, using the recently developed new analytical and modeling capabilities. Unprecedented maps of the D/H ratio in water were extracted from these data, and a paper was recently accepted by Science (see below). In addition, he participated in several international conferences and collaborated on several Titan and cometary projects.

4 Institutions
3 Teams
7 Publications
3 Field Sites
Field Sites

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.

Isotopic enrichment as evidence for global loss of water on Mars after Villanueva et al. 2015 (Science). After correcting for local climatological fractionation of the measured D/H ratio, the current ratio for D/H in atmospheric water on Mars is at least 7 VSMOW, implying a D/H ratio of 8 VSMOW in the north polar reservoir (red curve and right axis). Assuming a fractionation factor (f) of 0.02 and taking the D/H ratios obtained from water in Mars meteorites (Yamato 980459, of 4.5 Ga age) to be primordial, our D/H enrichments imply that Mars’ initial water reservoir was larger than the current water available on Mars by a factor of at least 6.5 (blue curve and left axis). When considering the current PLD content of 21 m of water, this would imply that at least 137 m GEL (global equivalent layer) of water was present on Mars 4.5 Ga ago, covering 19% of the planet’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.

    Geronimo Villanueva
    Project Investigator

    Michael Mumma

    Objective 1.1
    Formation and evolution of habitable planets.

    Objective 2.1
    Mars exploration.

    Objective 3.1
    Sources of prebiotic materials and catalysts

    Objective 3.2
    Origins and evolution of functional biomolecules

    Objective 4.1
    Earth's early biosphere.

    Objective 7.1
    Biosignatures to be sought in Solar System materials