By: Jerry Grula
Posted: November 25, 2025
Most geologists focus their efforts downward, studying the structure of the Earth. But Dr. Phil Christensen focuses on the heavens. Phil is a Regents Professor and the Ed and Helen Korrick Professor in the School of Earth and Space Exploration at Arizona State University. His research interests center on the composition, processes, and physical properties of interstellar surfaces. A major component of his research is the development of spacecraft instruments. Guided byPhil’s leadership, ASU has built a lengthy history of participation in planetary exploration, including the development of nine instruments for NASA and international missions to explore Mars, asteroids, and Europa, a moon of Jupiter with a subsurface ocean that may contain life.
Phil is also a frequent OLLI instructor, providing classes on topics including the inner terrestrial planets, the outer gaseous planets, the moons of Jupiter and Saturn, the Earth’s Moon, the asteroid belt, and the formation of our solar system.
His most recent class focused on key unanswered questions about Mars, including past climates and the potential of life. It then discussed the process of how an actual space mission is built, following the steps from the initial concept through the design, fabrication, and testing of spacecraft and instruments.
The final day included a tour of ASU’s extensive meteorite collection at the Buseck Center for Meteorite studies, and the labs on ASU’s Tempe campus where space instruments are designed and built.
Phil is extremely adept at breaking down technical subject matter into easy-to-understand pieces. No technology background is required for his courses – instead, you need only bring your interest in space exploration!
His class for the upcoming Spring 2026 semester is entitled “Invisible Worlds: Infrared & the Secrets of Light.” The light visible to human eyes represents only a small portion of the electromagnetic spectrum. Infrared light has longer wavelengths than visible light – although we cannot see it, cameras equipped with special detectors can. In this class, we’ll explore electromagnetic energy and demonstrate an infrared camera in action. Infrared observations are invaluable for studying the Earth, as well as other planets, moons, and asteroids. We will also discuss their role in monitoring global warming and greenhouse gases on our planet.
Look for this class in the catalog released December 1, 2025. Infrared cameras are Phil’s specialty, and he looks forward to sharing his passion and knowledge with you!
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I sat down with Phil recently to learn more about how he became a “space geologist,” the work he does at ASU, and his interest in teaching OLLI classes.
OLLI: What sparked your interest in geology, and how did that lead to you studying other celestial bodies?
Phil: As a young boy in the western US, our family took long car trips for vacation. Staring out the window, I was intrigued by the differences in the landscapes – why was Kansas so flat, while Colorado was so mountainous? I was also a child of the Apollo era, and when my mom got me a telescope, I found that I had the same types of questions about the Moon.
Not realizing that I could make a career out of both interests, I graduated with a geology degree and was ready to start a job doing oil exploration in the Middle East. As luck would have it, my friend told me about a professor who was studying Mars and was looking for someone to help him. I spoke with the professor, got the job, enrolled in graduate school, and began my lifelong work on space exploration.
OLLI: How do you, your students, and ASU participate in space research?
Phil: Our research is funded through NASA. When NASA announces a mission, we go through a comprehensive application process. It is time-consuming, but if we are selected, the resulting project results in significant work for our employees and students, as well as prestige and funding for ASU. I spend about 50% of my time on research activities, with 30% on classroom teaching and 20% on service activities.
Our current project is an infrared (IR) camera for the Europa mission. Each mineral has a unique frequency spectrum that will be measured by our camera. My students are currently measuring the spectrum of minerals to build a library, and when data starts coming in from the mission in 2030, they will analyze that data to identify the minerals.
We’re also excited about a new Moon mission we were awarded just before the government shutdown. There are craters near the poles of the Moon which are never exposed to sunlight, so we are going to help investigate them for signs of ice.
OLLI: Do you leverage commercial technology for your cameras?
Phil: Yes, but we can’t just use off-the-shelf equipment. Our instruments need to survive the massive shock and vibration of liftoff, extreme temperatures, and significant radiation, to name a few factors. And they absolutely cannot fail, so we build in redundancy wherever possible. But accommodating these factors adds weight, which is bad for space flight. It’s a huge engineering challenge. As a scientist I’m supposed to be more interested in the “why” and “what” than the “how,” but over time I’ve become increasingly intrigued with the puzzle of making these instruments meet requirements.
OLLI: In your opinion, what is the most important question being addressed in your field?
Phil: Is there, or was there ever, life on other bodies? It’s a question we’ve wondered for centuries, but now we have the technology to answer it. If there is life, what is it? Why did that type of life evolve in the specific environment? And if there was never life, why not? What was different about the environment that prohibited it? Obviously we hope to find signs of life, but there is value in the result regardless of the outcome.
OLLI: If you could go to any other body, what would it be and why?
Phil: Definitely Mars. Europa is interesting because it is an ice moon with liquid water beneath the surface, so it is the most likely location for life in our solar system. But to a geologist, it’s just ice. Mars is far more interesting to me. We can see ravines in places that were likely carved by water, and in shady areas, we have visual evidence of a material which might be water. I’m convinced that it is, but my colleagues aren’t. I’d love to investigate it and find out!
Also, on Earth the tectonic activity churns the planetary surface over time, so none of the rocks we see are that old, geologically speaking. Mars lacks that activity, so its rocks are 4.5 billion years old. Was there water at the beginning of the solar system? Was it acidic? What minerals were there? There is much we can learn about that time that can help us piece together information about Earth.
One of the things I like most about combining geology and astronomy is that I get to think big in terms of both time and space!
OLLI: Why do you teach OLLI classes?
Phil: I love teaching OLLI classes! Every student is there because they are truly interested in the material. Everyone is engaged. That helps me to be more into teaching the material. It’s like a good concert crowd – if the crowd is into the performance, the band feeds off that energy.
It also helps me to figure out how to explain things in their simplest, most understandable forms. I’m not an instructor who likes to stand in front of a class and show students how smart I am. In fact, I think too many students believe that the people who work on NASA missions are all geniuses. We’re not; we’re just normal people with a passion for our field. Anyone can do it!
OLLI: Finally, what’s next on tap for you at OLLI?
Phil: For the Spring 2026 semester I’m going to focus on IR cameras. I’ve taught classes on various aspects of our solar system, but the common thread in all of them is the cameras we use on the missions. I plan to explain how they work, and to let people use them and experience first hand the images we get.
OLLI: Thanks Phil, that sounds great, and thanks for your time for this interview!
Phil: My pleasure!
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Please look for Phil’s class entitled “Invisible Worlds: Infrared & the Secrets of Light” in the December 2025 OLLI catalog!
About the Author:
Jerry Grula is a retired technology business leader with experience in sales, marketing, product management, consulting, and engineering. He grew up in northeast Pennsylvania and moved to Phoenix in 1989, where he started his career and met his wife. He has a BS in Electrical Engineering from MIT and an MBA from ASU, and all three of his children are Sun Devil graduates. His interests include golf, exercise, sports, puzzles, music, fantasy football, technology, lifelong learning, and helping to publish the ASU OLLI Blog.
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