I completed my PhD in Astrophysical and Planetary Sciences at CU Boulder from 2017-2023, working at the Laboratory for Atmospheric and Space Physics with Mike Chaffin and the MAVEN team.
Thesis: The Variability of Atmospheric D/H on Mars
In planetary, our dissertations are basically “three papers stapled together” (plus some waxing poetic in an introductory chapter and wrap up chapters). The three papers included above are also found published in the literature (see end of this page). 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.
As with all dissertations, mine was wrong by the time it was done. For the third chapter, please see Cangi+2024 below in the publication list. It went through substantial revisions before being finally published (with thanks to Roger Yelle for feedback).
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, affecting its habitability. In a few words, 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). Yung+1988 quoted a value of 0.32 for D/H fractionation via thermal escape, but non-thermal methods are much more important for D than H, making them critical to include. My 2023 paper accounts for non-thermal atmospheric chemistry processes, which had not been examined before, finding f ~0.04–0.07.
Below with the papers, I summarize a take away of each paper in a few words.
- 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.