Daniel Yiu Wah Lo

I study planets in our Solar System.

My interests lie in using remote sensing techniques to observe the atmospheres and surfaces of terrestrial planets, and to understand the physical and chemical processes currently active in the atmosphere, on the surface, and at the atmosphere-surface interface. Currently 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.

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

The Spacecraft and Instrument: MAVEN/IUVS

Launched in 2013, the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission is NASA's latest spacecraft to Mars. With an orbit of 4.5 hours that goes down to 150 km and up to 6500 km above the surface, MAVEN provides 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 ultraviolet 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 various processes that occur in the Martian atmosphere today.

1. Tracing Atmospheric Loss

The evolution of the Martian atmosphere has been a long-standing mystery. Ancient channels and deltas record a time when there was liquid water flowing on the surface, carving the landscape, and collecting to form standing lakes. However, with a surface pressure of 6 millibars, the predominantly CO2 atmosphere of today is too thin to support liquid water. Hundreds of millibars of CO2 is required, and it is believed that most of the CO2 has been lost to space over the history of the planet. CO2 is broken up into the constituent C and O atoms via photochemical reactions in the upper atmosphere, and these C and O atoms can then escape into space if they have sufficient energy. One source of energy is from the photochemical reactions themselves. MAVEN/IUVS observations of the unique spectral signatures associated with various atmospheric species and reactions allow us to characterize the densities of key atmospheric species (such as CO, O and C), the rates of the photochemical reactions they are involved in, and how these vary both spatially and temporally. The successful application of these observations as constraints in our model to understand photochemical loss as it occurs today is a crucial step before we can trace loss rates backwards in time to unravel the evolutionary history of the Martian atmosphere.

Tidal variations of CO2+ ultraviolet doublet emissions with longitude (Lo, et al. 2015)

2. Identifying Atmospheric Tides

Thermal tides describe the "breathing" of the Martian atmosphere, expansion and contraction of the atmosphere in response to the diurnal heating by the Sun. These tides manifest as oscillations in density, pressure and temperature with periods which are harmonics of the Martian day. These oscillations have been observed throughout the atmosphere, and can be large — density variations of 20% are typical. Tides thus play a significant role in the diurnal circulation and transport in the Martian atmosphere. MAVEN is able to observe these tides through variations in the CO2 density as its orbit brings it across different latitudes, longitudes and times of the Martian day.

Credit: NASA GSFC/MAVEN/Univ. of Colorado

3. Monitoring Clouds

Temperature changes in the Martian atmosphere can result in condensation of its main constituent CO2 and the formation of clouds. These clouds show up conspicuously in MAVEN/IUVS images as localized regions with strongly scattered sunlight. MAVEN's non-sun-synchronous orbit allows IUVS to observe the distribution of clouds over the course of a Martian day, providing us with a unique dataset to study the processes that drive cloud formation and dissipation.

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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.

University of Arizona, USA

Master of Science, 2017. Major in Planetary Sciences.

University of Arizona, USA

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

California Institute of Technology, USA

Selected Bibliography

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

Conference Presentations

MAVEN IUVS Observations of C I Emissions at 156.1 nm and 165.7 nm. Mars Aeronomy Conference 2017.

Twilight Limb Observations of the Martian North Polar Hood by MAVEN IUVS. Division of Planetary Science/European Planetary Science Conference 2016.

Twilight Limb Observations of Clouds in the Martian Atmosphere by MAVEN IUVS. Lunar and Planetary Science Conference 2016.

Tides in the Martian Atmosphere as Observed by MAVEN IUVS. American Geophysical Union Fall Meeting 2015.

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)

Teaching Experience

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

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

Teaching Assistant for ASTR/PTYS 170B2 (The Universe and Humanity: Origin and Destiny) at 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/Raffles Junior College teams to the Singapore Young Physicists’ Tournament (2010)

Honors and Awards

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

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

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