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Project Progress

The most comprehensive study of isotopic water in the atmosphere of Mars

During this reporting period, we published the first global maps of HDO and H₂O ever achieved for Mars (Villanueva et al., Science 2015). Our infrared measurements of atmospheric D/H on Mars reveal strong geographical variability and a D/H ratio in water much higher (7 VSMOW) than that in Earth’s ocean water, indicative of a significant loss of water from Mars (see Figure 1). The strong geographic and seasonal changes of D/H on Mars may point to the presence of multiple water reservoirs of varying sizes, which lose water to and (may) gain from the atmosphere over time.

We then advanced our investigation of D/H on Mars, by developing a new observational plan that combines the power of ALMA, Keck and MAVEN to obtain 3D maps of the water D/H signatures on Mars. We were awarded substantial time at these observatories, with the first ever ALMA science observations of Mars to be carried out in March/2016. Vertical profiles of the HDO/H₂O abundance to be acquired with ALMA, in concert with escape rates of D and H measured by MAVEN, will provide an unprecedented view of the water cycle on Mars and the significance of atmospheric transport, and will test the presence of additional water reservoirs on the planet.

Taken in context, our work on Mars water informs us of conditions affecting the origin and persistence of life on a second terrestrial planet, including establishing the initial inventory of water and its subsequent losses.

Unidentified chemistry on Mars? Strong tests of current photochemical models via global mapping of water, ozone, and sulfuretted species

For this investigation, we used maps of ozone (probed via O₂[a¹Δ_g] dayglow) and water across the Martian globe that we obtained in 2014. Ozone and water are powerful tracers of photochemical processes on Mars. Considering that water is a condensable with a multifaceted hydrological cycle and ozone is continuously being produced / destroyed on short-time scales, their maps can test the validity of current 3D photochemical and dynamical models. Ozone and water are closely linked through photochemistry and they are anticorrelated with each other, because atomic hydrogen (a photolysis product of water vapor) is a powerful catalyst for destroying ozone. Comparisons of maps derived from modern GCM models with our new measurement-based maps point to significant disagreement, which in some cases have been related to heterogeneous (gas-dust) chemistry beyond the classical gas-gas homogeneous reactions.

We also obtained the most sensitive search (ever) for sulphuretted species on Mars by employing radio observatories. This work led to improved limits on active volcanism on Mars (Khayat et al. 2015). It received important media coverage, with several articles reported in international and local newspapers.

Unique Spectroscopy and Imaging of Mars with Space Assets

We led a community-wide white paper on the scientific use of JWST for Mars (Villanueva et al., PASP 2015). The distinctive vantage point of JWST at the Sun-Earth Lagrange point (L2) will allow sampling the full observable disk of Mars, uniquely permitting the study of short-term phenomena, diurnal processes (across the East-West axis) and latitudinal processes between the hemispheres (including seasonal effects) with excellent spatial resolutions (~0.07 arcsec). Spectroscopic observations will be achievable with NIRSpec at a maximum resolving power of 2700 in the 0.7-5 µm spectral region (8000 in the 1-1.25 μm range). Imaging will be attainable with NIRCam at 4.3 μm and with two narrow filters near 2 μm, while the nightside will be accessible with several filters in the 0.5 to 2 μm wavelength range. This powerful suite of instruments will be a major asset for the exploration and characterization of Mars. Science cases include the mapping of the water D/H ratio, investigations of the Martian mesosphere by characterizing the non-LTE CO₂ emission at 4.3 μm, studies of chemical transport via observations of the O₂ nightglow at 1.27 um, high cadence mapping of the variable dust and water ice clouds, and sensitive searches for trace species and hydrated features on the Martian surface.

We co-authored the first paper describing an infrared spectrometer (NOMAD) on the ExoMars/Trace Gas Orbiter spacecraft (Vandaele et al. 2015). NOMAD will provide unprecedented sensitivity for trace gases (e.g., 25 pptv for methane, in solar occultation) and promises to revolutionize our knowledge of biomarker gases on our sister planet (N₂O, CH₄, etc.). We continued our participation in the mission preparations, with a more accelerated schedule in the last months of this reporting period, considering the imminent launch on 14 March 2016.

Detailed studies of comets using ground-based observatories:

We also published four 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. See the GCA project reports by Charnley et al., and DiSanti et al. for this reporting period.