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Remote Sensing and Planetary Processes:
An Interview with Dr. Alex Hayes

by Mark Hilverda. Published on February 18, 2013.

Dr. Alex Hayes
Dr. Hayes at the W. M. Keck Observatory on Mauna Kea in Hawai'i.

Dr. Alex Hayes is Assistant Professor of Astronomy at Cornell University. Hayes uses spacecraft-based remote sensing to study the properties of planetary surfaces, their interactions with the interior, and if present, atmosphere. Recently, he has focused on studying the coupling of surface, subsurface, and atmospheric processes on Titan and Mars.

Was there a person or event that ignited your interest in planetary science?

While in high school, I contacted professors at a number of colleges to ask about undergraduate research opportunities. By far, the most enthusiastic response I received was from Steve Squyres of Cornell University. At the time, Steve was developing a Mars mission that would eventually become the Mars Exploration Rovers (MER) Spirit and Opportunity. His response, which both welcomed and challenged me to work on his project, was the deciding factor in my decision to attend Cornell and pursue a BA in Astronomy. Steve, along with colleague Jim Bell, were both strong supporters of undergraduate research and let a number of us become intimately involved in the MER mission at an incredibly early stage of our careers. To this day, I maintain strong ties with many of the scientists involved in MER (currently approaching sol 3200 of its nominal 90 sol mission).

Since working on MER, I have had the good fortune to study with a collection of awe-inspiring scientists who have both supported my research and helped to reaffirm my interest in planetary science. Credit for igniting my initial interest, however, must go to Steve Squyres and Jim Bell. The experiences that they provided through the MER mission solidified my desire to pursue a career in solar system exploration.

What topics are your pursuing in some of your latest and upcoming research?

We just finished a paper on the physics of generating waves on Titan's hydrocarbon lakes. One of the most intriguing observations of the Cassini Mission to Saturn has been the mirror-like reflections seen from of many of Titan's lake surfaces. These observations are in stark contrast to the discovery of vast equatorial dune fields, which require winds capable of saltating sand-sized particles. On Earth, even light winds will create ripples on a lake that would inhibit mirror-like reflections. As it turns out, the winds predicted in Titan's polar regions during the observed specular reflections are below the threshold required to generate waves. Over the next few years, however, the winds are expected to pick up and potentially cross the wave generation threshold for the most probable liquid compositions.

Another current project, pursued in collaboration with Ryan Ewing of the University of Alabama, involves Titan's vast equatorial dune fields. These dunes, which are believed to consist of solid hydrocarbon particles (i.e., plastic!), form patterns that are indistinguishable from dune field patterns observed on Earth and Mars. By studying the detailed morphometry of these patterns, we are able to probe both the wind directions and timescales over which the dunes evolved. This study will lead to important constraints that can help to understand Titan's long-term climate and hydrocarbon budget. The morphologies of individual dunes also reveal aspects of the sediment transport system and provide insight into parameters such as sediment supply and degree of equilibration with the modern wind regime.

Natucket Island and Ligeia Mare
LEFT: SEASAT-L Band (HH Polarization) SAR image southeast of Nantucket Island obtained in August 1978. The only dry land is Nantucket Island near the top right of the image, everything else is wave structure on the Ocean. (Credit: NASA/JPL) RIGHT: Cassini RADAR Ku-Band (HH Polarization) SAR image of Ligeia Mare on Titan acquired in 2006/2007. Note that the entire lake surfaces dark to the RADAR, suggesting little to no wave activity (Credit: NASA/JPL, Cornell).

On Mars, I have been collaborating with various members of the MSL science team to study the Curiosity landing site using a combination of orbital and rover-based images. Some specific projects include the origin and evolution of the Peace Vallis Alluvial Fan, quantification of fans generated from debris flows on the east side of Gale, photometric properties of Martian soils, and structure of Gale Crater. I look forward to developing these projects as the MSL mission matures.

As far as upcoming research goes, we were recently funded to study the evolution of Titan's polar landscapes using a combination of radar and infrared cameras on the Cassini spacecraft. The innovative part of this project is the incorporation of newly generated Digital Terrain Models (DTMs). The topographic information provided by DTMs has opened new doors for Titan research by allowing the quantitative analysis of morphologic form. For the first time, three-dimensional landscape relationships can be used to study surface evolution on Titan. Previous work on Titan's geology has been limited to a description of the observed morphologies. In our work, we will use topographic information to study the relationships between these morphologies and use that information to read the history of the landscape. I am very excited about this project not only because of the topic, but also because the proposal included a collection of well-known experts who will all be working together to solve this problem.

There are also a collection of smaller projects that involve Venus, Europa, and Io. Ultimately, however, I am most excited about the projects that I do not yet know about. In January I joined the faculty of Cornell's Astronomy Department. As a result, the interests of my students will drive the direction of my future research. I cannot express how excited I am to be heading back to Cornell and have the chance to work with both undergraduate and graduate students.

How useful are Earth analogs for studying processes on other worlds such as your sedimentology research on Mars? Do they provide a useful starting point or sometimes provide too much bias on initial interpretations?

If treated carefully, Earth analogs are invaluable for studying processes on other bodies. Sedimentary rock outcrops observed by the MER and MSL rovers are a great example. The geometry, scale, and distribution of the bedding layers in these outcrops are strikingly similar to deposits found on Earth and allow the methods and principles of terrestrial-based sedimentology to be utilized on their Martian analogs. Where you have to be careful, however, is when you blindly apply Earth analogs to other bodies without understanding the physics behind the underlying process that generated the structure you are studying. If any of the underlying mechanisms have a strong dependence on environmental parameters such gravity or atmospheric density, you need to scale your models appropriately.

Transport systems on Earth, Mars and Titan
Source-to-sink sediment transport systems on Earth, Mars, and Titan. A: Oblique aerial photograph of a source region on Earth, where runoff results in bedrock channel incision (Credit: Petroleum Development, Oman). B: LANDSAT 7 image of a sediment sink on Earth where a river delta deposits material at the edge of the continent (Credit: NASA). C: CTX image of a source region of Mars with a well-developed branching stream network (Credit: NASA, MSSS). D: CTX image of Eberwalde Delta on Mars (Credit: NASA, MSSS). E: Image of a branching channel network obtained by the Huygens probe during its decent (Credit: NASA, ESA). F: SAR image of a potential alluvial fan near Elvigar Flumina on Titan (Credit: NASA, JPL). Adapted from Figure 2 of J. Grotzinger, A. G. Hayes, M. O. Lamb, S. M. McLennan. Sedimentary Processes on the Earth, Mars, Titan, and Venus (in-press), In: M. Bullock and M. Mackwell (Eds) Comparative Climatology of Terrestrial Planets. 600pp., University of Arizona Press Space Science Series, University of Arizona Press, Tucson.

In addition to Mars, your research has a strong focus on Saturn's moon Titan. What attracted you to this hazy, hydrocarbon world?

Titan is a fascinating and dynamic place whose surface and atmosphere are affected by the same processes that we are familiar with here on Earth. On Titan you have active pluvial (rain), fluvial (rivers), lacustrine (lakes), aeolian (dunes), impact (craters), and potentially cyrovolcanic processes. It is the only moon with a substantial atmosphere (four times denser than Earth's) and the only place other than Earth that we know to have standing bodies of liquid. This makes Titan a natural laboratory for studying the basic principles behind the processes that affect our own surface-atmosphere system on Earth. Titan may also represent a hydrologic system that is common among extra-solar planets, as cooler M-Dwarfs are the most numerous stars in the galaxy and planets with water-based hydrologic systems orbiting M-Dwarfs would have to be too close their parent stars. In truth, however, my initial interest in Titan came from a meeting with the Cassini RADAR Principal Investigator Charles Elachi. He rolled a radar image of Titan's lakes across the hall in front of my graduate student office and told my advisor, Oded Aharonson, and I that he needed someone to analyze the data.

Hydrologic features of Titan
Distribution of hydrologic features in Titan's polar regions.

Planetary science often focuses individually on specific systems such as subsurface, surface or atmosphere. What are some of the challenges you face when studying the big picture, such as the interaction of multiple systems?

My research focusses on quantitative analysis of remote sensing data. This is a very broad topic that can be applied to many problems across subfields including optics, geomorphology, atmospheric science, oceanography, mineralogy, material science, etc. I cannot hope to be an expert in all of these topics, so when I need additional information for specific research projects I often partner with topical experts. An example is my recent paper on generating wind-waves on Titan's hydrocarbon seas. For this work, I collaborated with an oceanographer named Mark Donelan (University of Miami). Mark is an expert on the physics behind terrestrial wind-waves. For my current work on Titan's dunes I've partnered with aeolian expert Ryan Ewing (University of Alamba) and for the upcoming work on Titan's polar landscape evolution I'll be working with, among others, renowned geomorphologist Bill Dietrich (UC Berkeley). I enjoy working on a range of topics and learning from my collaborators.

You are the first recipient of the newly created Ronald Greeley Early Career Award in Planetary Science. What kind of influence did Dr. Greeley have on your career?

Ronald Greeley was an icon in the field of planetary science. In addition to his fundamental scientific contributions in the field of planetary surface geomorphology (from which I benefited greatly), Ron is also remembered for his mentorship and support of early-career scientists. Though I never worked with him directly Ron always took the time, whether we met during a conference or a Viennese concert, to stop what he was doing and ask me how things were going. That kind of genuine interest is rare among scientists of Ron's caliber and reputation and can go a long way toward encouraging early-career scientists.

You have recently become the director of the Spacecraft Planetary Imaging Facility (SPIF) at Cornell. In addition to supporting research activities, SPIF also focuses on public education and outreach. Which topics seem to be most popular in SPIF's outreach programs? What are some of the most successful approaches to distilling the vast amounts of available information to the public?

SPIF is one of NASA's Regional Planetary Imaging Facilities (RPIF). These centers are dedicated to disseminating and popularizing planetary spacecraft data to researchers, K-12 students, and the general public. SPIF's most popular outreach programs center around presentations and workshops given by our data manager Rick Kline using images from the latest planetary missions (e.g., MER, MSL, and Cassini). Over the next year, however, we will attempt to reach a wider audience.

The Paleontological Research Institute (PRI) is an Ithaca-based museum and research center that has been working with the National Science Foundation to bring Virtual Field Experiences (VFEs) to thousands of Earth Science classrooms across the country. A VFE is a collection of digital data obtained at a field site (e.g, the Mississippi River) and digitized in such a fashion that students can ask questions and learn about the landscape remotely. At SPIF, we will generate extraterrestrial VFEs (EVFEs) using data from the MER and MSL spacecraft. These EVEFs will then be disseminated using PRI's existing distribution network, allowing us interact with thousands of students in a short timeframe! If this program works, we'll try looking for additional collaborations where we can use existing distribution networks to popularize data from spacecraft missions (e.g., Khan Academy).

SPIF school visit
Students from the Immaculate Conception School, who visited SPIF on June 15th, 2012. Image credit: Rick Kline, Cornell SPIF.

Based on your public outreach work, what level of interest do you think exists for people to pursue careers in planetary science? Any recommendations and advice for those considering planetary science as a career?

Planetary Science is a broad field that covers many potential research areas. In terms of interest, I would imagine that many people would find working on active NASA missions as exciting and invigorating as I do. However, I would also point out that an education in Planetary Science is applicable to a broad range of career choices that extend beyond NASA and traditional academia. Before returning to graduate school, I spent a few years working at MIT Lincoln Laboratory (MITLL) on ballistic missile and other tactical defense projects for the US Air Force. The skills I obtained while working on the MER mission were directly applicable to my work at MITLL. Other career options for Planetary Scientists include resource management, aerospace, and exploratory geology.

A concluding, fun “what-if” question: If you could design any mission to Titan, what type of data would you be most interested in collecting?

This one is easy as the mission has already been designed. The Titan Mare Explorer (TiME) was a mission proposal to send a floating capsule to a Titan sea (Ligeia Mare). TiME was selected as one of the three finalists in NASA's recent discovery proposal. As many of you know InSight, a mission to send a seismometer to Mars, eventually won. In other words, NASA was on verge of launching the first extraterrestrial boat! In addition to being sensationally innovative, this mission was also scientifically compelling. We know very little about Titan, so even the most simplistic measurements of its surface would provide fundamental scientific advances.

If I could design any mission to Titan, it would be a lake lander that both sampled the liquid and took high resolution stereo images of the shoreline and surrounding terrain during its descent. If I could have two missions or one flagship class mission like Cassini, I would include an orbiter that could map the surface at 10 m resolution and generate global topographic maps.

TiME capsule
Artist's rendering of the TiME capsule floating in Titan's Ligeia Mare. Image credit: Johns Hopkins University Applied Physics Laboratory.

Reading Resources

Here is a collection of further reading resources compiled by Dr. Hayes for those interested in learning more on some of the topics briefly covered in this interview.

Where to Find Dr. Alex Hayes on the Web


Mark Hilverda is a geoscientist and Web Manager for the Planetary Sciences Section. He enjoys being where science, design, and technology collide. Feedback and suggestions for future articles and interviews are always welcome.