Interview With An Astronomer: William K. Hartmann
- Published: Monday, November 18 2013 18:01
Kitt Peak Solar Telescope by William K. Hartmann
Jon Ramer: Hi Bill, thanks for chatting with me. First, let me say congratulations on your recent award of the Shoemaker Distinguished Lunar Scientist Medal. Could you tell us a little about why you were awarded this honor?
William Hartmann: It’s primarily because my hair has turned grey. However, in addition, I had a long history of lunar work. As a graduate student I discovered the Orientale multi-ring impact basin working on a “rectified lunar atlas” project where we projected photos onto a globe and photographed features as seen “from above.” Once I saw the bull’s eye pattern, and then studied other basins I realized that all the big mare-lava basins have this pattern. I took the pictures to Kuiper and he let me be 1st author on a discovery paper, which we published in 1962.
Later in the 60s I studied the size distribution lunar craters, and developed the system for using crater counts (craters/km2) to estimate ages of lunar (and eventually Martian) surfaces. As early as 1965 I published a paper that correctly predicted the lunar mare lava plains were about 3.6 Gy old. In 1975, my Planetary Science Institute colleague, dynamicist Don Davis (who helped bring Apollo 13 back from the moon), and I published the paper that introduced what is now the leading theory of the moon’s origin, involving an impact by a giant planetesimal that threw Earth-mantle and impactor-mantle debris into Earth orbit, where it formed the moon.
JR: You are pretty well known for having come up with the Theia impact theory for the creation of the Moon. What led you to think of something like that in a time when such a theory would have been considered “radical”?
WKH: The discovery of the 1000-km scale Orientale basin on the moon really set me to thinking: “What was the largest impact ever to occur in the Earth-moon system?” Meanwhile, I had been reading papers by the then-little-known Soviet dynamicist, Viktor Safronov who was developing the mathematical theory of how planetesimals aggregated by collisions, to make planets. The biggest pre-Apollo problem about the moon was that it had almost no iron core. How could a body with no iron core form near Earth, which has a giant iron core. I realized that if a body hit Earth and blew out mantle material, the moon could form just from that rocky material (and would be relatively dry because the heat of the explosion would causes losses of water and other volatiles. I approached Don with the question: How large could the 2nd-largest planetesimal grow in the Earth-forming zone, while the Earth was forming. The models in our paper suggested that 2nd-largest bodies could reach sizes as large as Mars! I gave the paper at a 1974 conference and we published in Icarus in 1975.
JR: Being a space artist I’m sure you’ve painted a Theia impact image. Would you please share it with us?
WKH: I have a whole series of paintings about lunar origin, over the years; I start with other workers’ published computer models of the event, which usually produce cartoon-like black and white or false-color diagrams, and try to imagine: What would that have looked like if you were really there? I have a good friend, Larry McGlynn, who has an important collection of art and objects associated with space exploration. He acquired many of the paintings.
I attach one that shows the situation about an hour after the impact, averaging over several models. I like it because it emphasizes not only Earth’s disruption in an early stage of the collision, but also the amount of material being torn out of both bodies. Work by Dave Stevenson, Kaveh Pahlevan suggests that the mixing of that material may help explain why the present-day Earth and moon have such similar isotope patterns, even though the impactor material may have had somewhat different isotopes than proto-Earth.
The Moon, One Hour After Impact by William K. Hartmann
I attach another one that was really a scary painting, the more I looked at it. I wondered: What would it have looked like from proto-Earth, to see the moon bearing down on you. Of course, there was no probably no life yet, but still... The main problem is that I don’t think we know if proto-Earth’s atmosphere might have been opaque with clouds. But I imagined some cloud openings. This moment is only 5 or 10 minutes away from the impact, depending on how the impactor’s approach velocity. People often ask if the ocean shouldn’t be more violent; I’m not sure but the moon’s tidal forces affect the ocean as a whole, and besides, there has not been much time for Earth to react to the suddenly-appearing tidal forces!
Approach of Impactor by William K. Hartmann
JR: Your article mentions that you’ve painted many images while at IAAA workshops. How many workshops have you been to?
WKH: I’m not really sure. Hawaii twice, Iceland, Arches monument, Death Valley, Yellowstone park, Tenerife, Nicaragua, Flagstaff with our outings to Meteor Crater and Grand Canyon. Our mini-projects on Mt. Palomar and Kitt Peak. Our meetings hosted by the Russians in Moscow and the Crimea. Probably at least a dozen. Attached is a picture of the Kitt Peak solar telescope just before sunset - what a wonderful, surreal structure in that beautiful natural setting!
JR: Which one was your favorite and why?
WKH: One favorite was a sort of embryo workshop, the “first” one, which I organized at Volcano Art Center in Hawaii in 1982. It was not really any IAAA workshop, but it was the workshop at which our original group first met each other and bonded; IAAA formed a year later at the Death Valley workshop, organized by Mike Carroll. And we all loved Iceland! Well, they were all great experiences!
JR: What was your favorite workshop painting?
WKH: Ooooffff! That’s hard to say. I am partial to that Kitt Peak solar telescope image, just because it’s both odd and real at the same time, and I like the light effects. Here’s a 1996 view of the Teide volcano that I like. It’s hanging in my studio now. All of the workshop landscapes were painted almost entirely on site, outdoors, so I have strong and happy recollections of being totally immersed “in” each one of those places.
Tenerife Mt. Teide Volcano by William K. Hartmann
JR: You and I once sat on the side of Mount St Helens at an IAAA workshop discussing inspiration for space art. My “Eureka! That’s what I want to do!” painting was actually one of your images in your and Ron Miller’s wonderful book “The Grand Tour.” Did you have a similar image that made you want to paint space art?
WKH: It was definitely the work of Chesley Bonestell! Especially his painting of the silver rocket sitting on the moon, on the front cover of his 1949 book with Willy Ley, “Conquest of Space.” I was so happy to meet him and become friends with him and his wife Hulda late in their lives. It’s great if one of my images helped to inspire you! Thanks for saying that!
JR: Thanks very much for your time - and your wonderful art....
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