Thesis: The Variability of Atmospheric D/H on Mars
My dissertation focused on variations in the deuterium/hydrogen (D/H) ratio on Mars, and what they can tell us about recent and long-term loss of water from Mars and impacts to its habitability. My work has shown that the solar cycle and seasonal climate variations all can drive large variations in water loss via H and D escape to space. Using photochemical modeling, I revised estimates of the D/H fractionation factor f (the efficiency of D escape compared to H escape) to an average of ~0.055 (vs. the previous value of 0.32) by accounting for lower thermospheric temperatures measured in recent decades and non-thermal escape of D.
The primary chapters of the dissertation are also found published in the literature. Below I provide for you the ADS links so you can grab the copy either from the journal or arXiv if you don’t have institutional access to the journals. For the third chapter, please use Cangi+2024 below in the publication list. It went through substantial revisions before being finally published (with thanks to Roger Yelle for feedback).
- Cangi+ 2020: Higher Martian Atmospheric Temperatures at All Altitudes Increase the D/H Fractionation Factor and Water Loss
- Takeaway: Exospheric temperatures significantly alter the D/H fractionation.
- Cangi+ 2023: Fully Coupled Photochemistry of the Deuterated Ionosphere of Mars and Its Effects on Escape of H and D
- Takeaway: Non-thermal escape driven by chemistry below the exobase cannot be ignored in computing D/H fractionation, as it makes up the lion’s share of D escape.
- Cangi+ 2024: Seasonal Enhancement in Upper Atmospheric D/H at Mars Driven by Both Thermospheric Temperature and Mesospheric Water – Sorry, apparently I never put this one on arXiv, but you can get the open access copy on ESSOAR.
- Takeaway: the D/H ratio in atoms (H and D themselves) varies up to an order of magnitude throughout the year due to normal seasonal variations in temperature, water in the mesosphere, and insolation. The specific mechanisms are different for H and D and rather subtle, so you’ll have to read the paper for more on this one!’
Taken together, the overall conclusion is that escape to space of H and D must have been much greater in the past in order to reconcile what we know about escape today with the quantity of water that has been lost from Mars over time, inferred from geomorphological analysis.