Daniel Yiu Wah Lo

I study planets and moons in our Solar System.

My interests lie in using remote sensing techniques to observe the atmospheres and surfaces of terrestrial planetary bodies, and to understand the physical and chemical processes currently active in the atmosphere, on the surface, and at the atmosphere-surface interface. Currently also a science team member for the MAVEN mission to Mars, I make use of data from primarily the Imaging UltraViolet Spectrograph (IUVS) to study the processes that shape the Martian atmosphere today.

Current Projects

1. Climate change at Mars

More than 3.6 billion years ago, Mars had liquid water on its surface. Just like water on Earth today, this water carved the ancient Martian landscape, forming rivers, depositing deltas and collecting in standing lakes. There were even occasional waterfalls. Water was so prevalent then that this period of Martian history is referred to as the "Noachian Period" after the biblical flood.

Modern Mars, however, is exceedingly dry. Gone are the rivers and the lakes. With an average surface temperature of -63oC, H2O on Mars now mostly exists as ice in the polar caps and the subsurface. Although the atmosphere is made up of 95% CO2, the surface pressure of 6 millibars today is too low to produce sufficient greenhouse heating. For Mars to have been warm enough in the past to support liquid water on the surface, hundreds of millibars of CO2 would have been required, and it is believed that most of this CO2 has been lost to space.

To understand the past, we must first understand the present.

My research focuses on the processes behind the loss of the Martian atmosphere. One main process is photochemical escape. CO2 is broken up into the constituent C and O atoms by solar UV radiation, and these C and O fragments can then escape into space if they have sufficient energy. Through my research, I have found, among other results:

While these results apply to atmospheric loss from modern Mars, our characterization and understanding of the various loss processes form the foundation for further studies investigating atmospheric escape from ancient Mars, which had a thicker and warmer atmosphere, and orbited a younger Sun that emitted more intense UV radiation.

2. Monitoring the Martian Atmosphere

MAVEN/IUVS stellar occultation observations (Credit: NASA/GSFC Conceptual Image Lab)

Since its arrival at Mars in 2014, the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft has been providing us with an unprecedented view of Mars through its diverse suite of instruments. Among the instruments, the Imaging UltraViolet Spectrograph (IUVS) plays the role of the "official photographer" for the mission, snapping pictures in the UV of the atmosphere, the surface, and even the moons of Mars. My role in the team is to process and analyze these images to study the structure of the Martian atmosphere and the various processes that occur today.

While other orbiters at Mars have Sun-synchronous orbits that allow them to observe Mars at only two particular local times of the Martian day, MAVEN has a non-Sun-synchronous orbit, giving us a unique opportunity to study how various atmospheric phenomena change over the Martian day. By observing the UV radiation emitted by the atmosphere through IUVS, we are able to determine the temperature and composition of the atmosphere at various altitudes. UV images taken in the day and night tell us different information. In the day, the CO2+ UV doublet emission at 298–299 nm tells us the density of CO2 and the atmospheric temperature. We found regular fluctuations in atmospheric density and temperature over a Martian day due to thermal tides, in response to the diurnal heating by the Sun. A bright reflection of sunlight would be a cloud, possibly formed from a low temperature layer in the atmosphere, or the cooling of an air parcel when it is pushed up one of the tall mountains on the Tharsis plateau. At night, nitric oxide (NO) emissions allow us to trace atmospheric circulation.

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Abbreviated Curriculum Vitae

Click here to download a PDF of my full CV.


Doctor of Philosophy, in progress. Major in Planetary Sciences, Minor in Optical Sciences.

The University of Arizona, USA

Master of Science, 2017. Major in Planetary Sciences.

The University of Arizona, USA

Bachelor of Science with Honors, 2014. Double Major in Physics and Planetary Science, Minor in Philosophy.

California Institute of Technology, USA

Honors and Awards

Galileo Circle Scholarship (2019). The University of Arizona

GPSC Travel Grant (2018). The University of Arizona

Career Development Award (2018). Lunar and Planetary Institute

Group Achievement Award for Science — MAVEN Science Team (2016). NASA

Lieutenant Colonel Kenneth Rondo Carson and Virginia Bryan Carson Graduate Fellowship (2014). The University of Arizona

Fritz Burns Prize in Geology (2013). California Institute of Technology

Selected Bibliography

Lo D. Y., et. al. MAVEN/IUVS observations of C I emissions at 156.1 nm and 165.7 nm. In prep.

Lo D. Y., et. al. Carbon photochemical escape rates from the modern Mars atmosphere. Submitted to Icarus.

Lo D. Y., Yelle R. V., & Lillis R. J. (2020). Carbon photochemistry at Mars: Updates with recent data. Icarus, 114001. doi:10.1016/j.icarus.2020.114001

Ajello, J. M., Malone C. P., Evans J. S., Holsclaw G. M., Hoskins A. C., Jain S. K., McClintock W. E., Liu X., Veibell V., Deighan J. I., Gérard J.‐C., D. Y. Lo, & Schneider N. M. (2019). UV study of the Fourth Positive Band system of CO and O I 135.6 nm from electron impact on CO and CO2. Journal of Geophysical Research: Space Physics, 124. doi:10.1029/2018ja026308

Scheingross J. S., Lo D. Y., & Lamb M. P. (2017). Self-formed waterfall plunge pools in homogeneous rock. Geophysical Research Letters, 44 (1), 200–208. doi: 10.1002/2016GL071730

England S. L., Liu G., Withers P., Yiğit E., Lo D. Y., et. al. (2016). Simultaneous observations of atmospheric tides from combined in situ and remote observations at Mars from the MAVEN spacecraft. Journal of Geophysical Research: Planets, 121 (4), 594–607. doi:10.1002/2016JE004997

Lo D. Y., et. al. (2015). Nonmigrating tides in the Martian atmosphere as observed by MAVEN IUVS. Geophysical Research Letters, 42 (21), 9057–9063. doi:10.1002/2015GL066268

Scheingross J. S., Brun F., Lo D. Y., Omerdin K., & Lamb M. P. (2014). Experimental evidence for fluvial bedrock incision by suspended and bedload sediment. Geology, 42 (6), 523–526. doi:10.1130/G35432.1

Research Experience

Graduate Research Associate, Lunar and Planetary Laboratory, The University of Arizona (2017 – present)

Science team member for Mars Atmosphere and Volatile EvolutioN (MAVEN) (2014 – present)

Graduate Research Assistant, Lunar and Planetary Laboratory, The University of Arizona (2014 – 2017)

Caltech Summer Undergraduate Research Fellowship (2011, 2012, 2013)

Science Research Programme (2006)

Science Mentorship Programme (2004)

Teaching Experience

Member of Curriculum Development Committee at Lunar and Planetary Laboratory, The University of Arizona (2016 – 2017)

Teaching Assistant for ASTR/PTYS 170B2 (The Universe and Humanity: Origin and Destiny) at The University of Arizona (Spring 2017)

Teaching Assistant for ASTR/PTYS 170B2 (The Universe and Humanity: Origin and Destiny) at The University of Arizona (Fall 2015)

Coach for the Singapore national team to the International Young Physicists’ Tournament (2010)

Trainer for the Raffles Institution team to the Singapore Junior Physics Olympiad (2010)

Coach for the Raffles Institution and Raffles Junior College teams to the Singapore Young Physicists’ Tournament (2010)

Planetary Exploration Mission Experience

Science team member for the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission (2014 – present)

Project Manager for runner-up Caltech team to the RASC-AL Exploration Robo-Ops competition (2012)

Science instrumentation team member for winning team at Caltech Space Challenge (2011)

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