It has been a privilege to serve as a blogger for The Planetary Society at various planetary science conferences over the years. This was only the second time I’ve done it from the city in which I live, Knoxville, Tennessee. The 45th Binghamton Geomorphology Symposium, so named because it was originally based in Binghamton, New York, but now moves from year to year, was held at the University of Tennessee over the weekend. The theme of the Binghamton Geomorphology Symposium is usually terrestrial, but this year it was planetary science.
A real highlight of the symposium was Victor Baker’s survey of the history of planetary geomorphology, taking it all the way back to Galileo and Christiaan Huygens and looking at the philosophical struggles that affected the field over the years. Most of the pre-telescopic era was dominated by the struggle between authority on one side and reason on the other. In the earliest days, the struggle was against classical and church authorities who claimed the heavens were perfect and thus worlds should be smooth and featureless and telescopic observations which clearly showed lunar craters and planetary markings. Later, the struggle came between supposed authorities (for example, Grove Karl Gilbert, whose conclusion that lunar cratering was volcanic was used to marginalize those who supported the impact hypothesis) and people reaching conclusions doing original research.
Baker also talked about how in an era when planetary astronomy was largely funded by philanthropists, figures like Percival Lowell emerged. He related Lowell’s obsession with canals and his related theories of the dying Martian civilization to the work of the American philosopher Charles Sanders Peirce, whose “Fixation of Belief” beautifully describes Lowell and other crackpots.
"The Fixation of Belief"
Baker also appealed to Peirce when talking about the difficulties of doing geology, planetary or otherwise. Peirce wrote that “Geology is...the most difficult of the sciences, barring none. Concerning causes in nature that are not communicative...the invention of the right hypothesis requires genius” (“Review of ‘The Life of James Dwight Dana,’”1899). While papers often focus on how hypotheses are tested and students are taught a hypothesis, Baker spoke about how little emphasis is put on how to formulate a hypothesis, and often papers only explain the hypothesis and then how it is tested, not how it was formulated. Figuring out what to test is thus an overlooked challenge. And often the hypotheses tested are simply based on what people who are considered authorities in the field say should be tested, without any real discussion of how the hypotheses themselves were developed.
Returning to the theme of authority versus reason, Baker waded into some controversial waters, questioning our approach to exploring the Martian surface. He focused on NASA’s obsession with sending big, high-priced rovers, and then searching for a single site that would yield answers to the history of water on Mars and whether or not it had life. Imagine, he said, finding a single site from orbit to explain the history of water and life on Earth. He suggested that it would be more reasonable to send dozens of small landers and perhaps rovers to diverse sites, and then select where to send big missions from what we learned from the smaller ones. He argued that the problem lies in that the fact that the powers that be (in this case NASA and perhaps Congress) are fixated on the concept of one or a few large missions that will explain Mars, drowning out a reasoned approach to exploration.
Since I am a philosopher by trade, I was very pleased to see a well-received keynote that was philosophically driven, bringing together two areas that are of great importance to me. The other talks at the meeting were less philosophical, but ranged across a broad range of planetary geomorphology topics.
Amanda Nahm started out with a talk about tectonic features throughout the solar system. She gave a general survey, then compared normal faults on the moon and Enceladus to show how similar inferences could be made about lithospheric properties on both worlds. [Normal faulting happens where brittle rocks are being stretched apart, like in the African Rift Valley on Earth. --Ed.] Since normal faulting is nearly ubiquitous on solid worlds more than a few hundred kilometers across, this provides a relatively universal tool for comparing them.
Tectonic features: Enceladus vs. the Moon
Chloe Beddingfield, working with Devon Burr and William Dunne, created digital elevation models of some major tectonic features on Saturn’s large icy moons. She picked Ithaca Chasma on Tethys, Avaiki Chasmata on Rhea, and the wispy terrain on Dione, and then compared the slopes with laboratory models of water ice. They found the slopes to be much shallower than they expected. While mass wasting (landslides) may be the culprit, evidence for it is absent in the cross sections they studied. They proposed viscous relaxation and magmatic intrusion as possible explanations for the topography.
NASA / JPL / SSI
Dione's scarps and slopes
Cassini snapped this ultra-close view of Dione during its 500-kilometer flyby on April 7, 2010.
Beddingfield also presented a poster, along with Burr and Joshua Emery, on Miranda, where she argued for listric faulting (a type of normal faulting in which one of the layers falls away on the fault line, particularly near the surface) in Arden Corona. Interestingly, this model does not work for the large, global chasm best known for its giant cliffs seen on the terminator during Voyager’s closest approach.
Peter Cartwright, best known for his spectroscopic work on the Uranian moons and also working with Burr, presented a poster showing work he has been doing comparing Titan’s rivers with an ephemeral river in Namibia. By using both Landsat and SIR-C radar data, he is attempting to establish context for interpreting much lower-resolution Cassini Radar data to understand how material from the highlands is deposited by rivers, like the cobbles seen by the Huygens lander. Interpreting radar images is notoriously tricky, which is a major reason why comparing Titanian examples with terrestrial ones in which we have other sources of high resolution data is useful. His work included a test strip where he compared mapping of an area using visible and radar data.
Landsat and SIR-C radar data
Alexander Hayes did a survey of solar system lakes, examining earth and Mars before focusing on Titan. He explained how differences in the seasonal patterns in the north and south of Titan explain why most of the filled lakes are currently in the North, although over long periods of time this changes. Radar measurements earlier in the Cassini mission taken of Ontario Lacus showed that the surface was flat. However, in the last few years, several ephemeral islands have emerged, and radar data returned in the last month shows that some small waves may be starting to kick up on the lakes.
Additionally, Cassini did an altimetry pass across Ligeia Mare that detected both the surface and the bottom of the lake. The data show that its deepest areas are about 200 meters deep. This, combined with the detection of the bottom in itself, indicates that Ligeia Mare is almost pure methane. Traditional models of Titan’s lakes assume a large ethane component, but an ethane content of more than a few percent would have obscured the lake bottom at such depths from Cassini’s radar.
There were a lot of Mars presentations, mostly focusing on water flows and Aeolian processes. Covering them would be another blog entry. As a group, they demonstrated that, due to the relatively intense coverage it has gotten in comparison with other planets, papers on Mars are becoming very regionally specific. Increasingly, Mars papers resemble terrestrial papers. For example, Keenan Golder’s poster showed a geologic map of Ceberus Fossae made taking advantage of the CTX imager on the Mars Reconnaissance Orbiter. CTX is a workhorse that is overshadowed by the sharper-eyed HIRISE. CTX has provided nearly global coverage of Mars with resolutions of a few meters, allowing us to study small features over large areas. It was interesting to see how many people working with such data sets, as well as with Curiosity, are terrestrial geologists crossing over to Mars. Linda Kah, one of the keynote speakers, had never done extraterrestrial geology before, leading to her great surprise at other investigators' excitement when, for example, Curiosity discovered a conglomerate early in its mission (It was the first unambiguous example of one identified on the Martian surface).
NASA / JPL / MSSS / Ed Truthan
Hottah, a conglomerate rock formation in Gale crater, Curiosity sol 39
A nine-image color Mastcam-100 mosaic of some tilted blocks of rock seen by Curiosity during its drive to Glenelg, sol 39 (September 15, 2012).
The symposium, both in terms of the research presented as Victor Baker’s use of history to play the role of gadfly, was quite a success.