Guide to Mars: Interview with Bill Hartmann
Traveler’s Guide to Mars
Interview with Bill Hartmann
If the nascent field of astrobiology crosses many faculties– microbiology, oceanography, planetary science, and geology–then the work of the Planetary Science Institute’s Bill Hartmann crosses entire departmental studies. Hartmann’s reach doesn’t have to extend across the hall, but across the campus. His work could appear in the art or astronomy department. He reflects this when he writes that "in my terrestrial landscape painting, I see Earth is a cosmic body — just one of many worlds." While many scientists have a gift for thinking visually, Hartmann has the rare ability also to show others visually what he is thinking. In addition to painting, Hartmann has written science-fiction about Mars, which Sir Arthur C. Clarke reviewed as conveying "a realistic feeling about the future development of Mars." His most recent "Traveler’s Guide to Mars", has entered its second printing after just a few months.
But Hartmann remains committed to science, as inspiration and a basis for understanding the physical universe. Since the early 1970’s, when he was co-investigator with Caltech’s Bruce Murray and Cornell’s Carl Sagan on the Mariner 9 mission, he has marvelled at pictures of the red planet. Mariner 9 discovered the erosion patterns which today, have been refined and become the focus of the debate about whether surface water once existed on Mars. His recent work on the imagery from the Mars Global Surveyor, has given a detailed view of surface objects about the size of a school bus.
Astrobiology Magazine had the opportunity to talk with Hartmann about his interests and the prospects for three landing missions this winter on Mars.
|Layered martian terrain in painting by Bill Hartmann (left), orbital image from Mars Orbital Camera (right).
Copyright William K. Hartmann
Can you walk through the synopsis of how you came to span these diverse fields?
Bill Hartmann (BH): One of my grandfathers was a painter and the other a mathematician who published an early paper on relativity — and now I’m left wondering if I inherited some disposition…or is it all social/familial environment? I set aside an early "play" interest in drawing to pursue physics, geology, and astronomy in graduate school, in order to study planets. After the Ph.D., I had an offer to do a textbook which grew into several textbooks.
Since 1960’s texts were dull, black-and-white affairs, with few pictures, I thought it would be good in my textbooks if I could use Chesley-Bonestell-like artist’s conceptions of astronomical settings to give students a better sense of what we are talking about. [Chesley Bonestell is considered the father of modern space art].
I met a number of other astronomical artists, and kept moving in that direction, as well as doing my scientific work. Also, the more I wrote research papers, then popular books, the more I wanted a wider range of creative expression of what I had learned about life and society, and that led to two novels called "Mars Underground" and "Cities of Gold".
So it was a set of expanding horizons — expanding beyond the strictures of science per se (but science is still the best way to learn about the physical universe).
AM: How did you get started with your new book, "A Traveler’s Guide to Mars"? The book has been well received, sold out its first 30,000 copies and went into a second printing within two months.
BH: When the publisher and I decided to make it a "Traveler’s Guide," I picked about three dozen exciting places on Mars, and then used new and old photos to weave them into a story about how Mars itself has evolved.
I’m using it as an experiment to see if a popular science book can be used to help support research at our Planetary Science Institute. As noted in the front matter, 25% of the royalties will go to the Institute, which in turn has moved to a new expanded building which we hope to buy to provide a permanent, stable home for a good research group and a number of young student assistants.
AM: Your research pioneered some new methods for determining the age of planets and moons by crater counts. A NASA Ames project on the internet– called clickworkers— continued this for Mars, where orbital images where projected, and volunteers counted the craters in a distributed way that was unavailable without big computing power. How do crater counts give the age of a surface on Mars?
|Frost on one side of embankment
Credit: NASA/ JPL/ MSSS MOC
BH: Our technique at the Planetary Science Institute is to use the moon as calibration. We know the crater densities (i.e. diameter distribution) for lunar lava plains that are about 3.3 to 3.9 billion years old. Then we use dynamical estimates from observed asteroids and theory of asteroid scattering out of belt resonances [between planetary influences on orbits], to estimate the ratio of Mars/moon impacts for fixed size asteroids. Then we apply some scaling factors for gravity and impact velocity. Voila! We have the predicted crater density on Mars for 3.5 billion years; and from time dependencies measured on the moon and Earth, we have estimated time dependence, so we can predict "isochrons" or diameter distributions, for different ages on Mars.
Much of this is described in a tutorial.
AM: When there are so many weathering effects on a place like Mars relative to the moon, what is learned about relative ages from crater counts, when the surface is being modified?
|Rugged terrain on Mars
Credit: NASA/ JPL/ MSSS MOC
BH: That’s a big current question for me.
I started out making the comparisons with young, well-preserved lava flow surfaces on Mars. (I was gratified that my estimated ages of few hundred million years were consistent with Mars meteorite ages for basaltic lava flows and igneous rocks from Mars). As we go to older surfaces, erosive and depositional processes preferentially remove smaller craters. Measurement of that effect (currently underway in our program) will give some information on the erosive/depositional regimes as a function of time on Mars.
Preliminary results support earlier estimates that Noachian early Mars [Noachian, the earliest period on Mars, when high impact cratering rates formed densely cratered terrains still preserved on 40% of the planet] had ten to a hundred (1-2 orders of magnitude) higher rates of resurfacing by volcanism, fluvial processes, glacial processes, etc. — on average.
AM: Do you have a sense of what the two Mars landing sites in January–Gusev Crater , potentially a dry lakebed, and Terra Meridiani, where water-formed rocks may be found–are going to offer that is unique compared to previous sites. For instance, the understanding of how surface water might have played a role in reshaping the geology and erosion?
|Viking image of Gusev Crater, an ancient proposed lakebed that will be targeted in the forthcoming Mars Exploration Rover mission.
My favorite is Terra Meridiani, because hematite mineral concentrations are detected there, possibly due to hydrothermal activity, and our crater studies (with Dr. Melissa Lane in our group) suggest a very old surface (a lakebed?) that was only recently exhumed.
A problem I see for all three landing exploration plans is that, in general, Noachian lakebeds will not be well preserved.
Mars is cratered down to sizes of a few meters or less, and according to a recent paper of mine, impact gardening will chew up the surfaces in less than one billion years. So…you can’t pick out Noachian lakebeds and expect them to be intact at the exploration scale of 1-10 meters (~3 to 30 feet).
That’s why I like Terra Meridiani, where we may get lucky and see a surface that has been covered, preserved, and then exposed by exuhumation only a few million years ago.
AM: As co-investigator with Caltech’s Bruce Murray and Cornell’s Carl Sagan on Mariner 9, that mission discovered the dry river channels that are now so intriguing when shown in fine detail as gullies and winding erosion patterns. What is your opinion on how the debates about Martian water have changed from the early 1970’s Mariner images to the late 1990’s Mars Global Surveyor pictures?
BH: The "idea" of Mars went thru a nadir after early Mariner in the 1960s when craters were seen ("Mars is dead like the moon") and then in 1976 when Viking found sterile soil ("Mars is really dead like the moon.")
Since then I think its astrobiological stock has been climbing.
We’ve seen very young geology from crater counts, and we have lava rocks from Mars formed only 170 million years ago. We found that soils can be sterile in Antarctica while nearby rocks (and subsurface?) have microbial activity; we’ve discovered water is actively released on Mars (even if only sporadically) in recent time; two labs have dated a water exposure in a Martian meteorite at around 670 million years; and recent terrestrial studies have suggested the presence of microbes that can go dormant in ancient rocks for periods up to 250 million years! Not to mention the claims of direct detection of microbial fossils in the Allen Hills Martian (ALH-84001) meteor. Could life have evolved in the early, more water-rich environment of Mars, and then have evolved to survive dry periods between sporadic water activity?
It’s a long shot, maybe, but I see it as a very open, exciting question.
AM: Orbital projections of where the Mars Exploration Rovers are right now, can be continuously monitored over their half-year journeys, which culminate in their landing around January 2004. You work directly with the Mars Global Surveyor (MGS) team. How are those images being used during the actual rover missions in January, if at all?
BH: MGS images are by far the highest resolution images of Mars, so they are critical to choosing general landing areas, and determining positions of features observed, we hope, by the three rovers.
AM: Is it correct that the resolution (around 10 meters) is capable of seeing under good conditions, something around the size of school bus approximately?
BH: Yes. On the best MGS images, we feel we get good crater statistics, for example, down to 11 meters diameter
AM: You also worked with D.R. Davis on what has become the leading theory of the origin of the moon–the giant impact that blew out rocky debris from the earth. Most searches today in the near-Earth asteroid field, always view the terrestrial neighborhood as a dangerous place for impacts. Do you find it ironic that life as we know it on Earth couldn’t exist without the moon, but the moon couldn’t exist without an equivalently devastating early ‘extinction-scale’ event like the giant impact?
|Half an hour after the Giant Impact, based on computer modeling by A. Cameron, W. Benz, J. Melosh, and others.
Copyright William K. Hartmann
BH: What I think is ironic is the simple idea, that most lay-people still don’t get, that shooting stars, meteorites, the impact that wiped out the dinosaurs, possible impact control over evolution, and the origin of the moon, are all controlled and explained by a simple diameter distribution of asteroid fragments that can be duplicated by smashing rocks in your back yard. Meanwhile, "our" fundamentalist generals are fighting "their" fundamentalist fanatics over issues that were more or less resolved and should have been settled in the 1700s. Sigh.
AM: In the 1980’s you were part of the Hawaiian Mauna Kea team that first proposed comets as being very dark, coal-like surfaces. Is it surprising given that as a comet is closer in its solar orbit, the solar wind makes it so intensely bright to casual observers?
BH: Dale Cruikshank, Dave Tholen, and I found that outer solar system asteroids and comets all have similar dark colors, apparently due to carbonaceous sooty compounds. The cometary ices are mixed in, but the mix has a dark color. Before that, people thought comets were bright, like icebergs with a little dirt on them. Note that solar wind doesn’t affect the reflectivity. Proximity to the sun just heats the ice and drives off the gas, hence creating a coma, hence making the cometary object much brighter than at large solar distance.
AM: What is your sense of what comets may have to offer astrobiology, in that they likely have some water content, and perhaps after the Jupiter impacts, a kind of destiny with meeting up over very long times with even more habitable places like Earth or Mars?
BH: Comets for sure have water and organic materials, as do carbonaceous chondrite meteorites [stony meteors with hydrocarbons] and interstellar dust. But my sense is that these very facts prove that water and organics synthesize themselves easily and naturally when conditions are anywhere near right — so we don’t need comets per se to provide organics to form life.
They’re handy to have, I suppose, if everything else fails….
AM: As a painter, what kinds of astronomical images most inspire your work? The Hubble galaxies, or the planetary surfaces?
BH: I tend to like surfaces, since I can relate them to effects and formations I observe directly from nature when I paint outdoors at sites such as Kilauea Volcano (Hawaii),Pinacate volcano and desert (Mexico), Iceland, Tenerife (Canary Islands), and the Sonoran desert here in Arizona. Examples are on my home page at our institute web site.