MINUTES OF THE
MARS CRATER MORPHOLOGY CONSORTIUM MEETING IV
US GEOLOGICAL SURVEY, FLAGSTAFF, ARIZONA
OCTOBER 11-12, 2001
Attendees: Nadine Barlow (U. Central FL), Joe Boyce (NASA), Trent Hare (USGS), Horton Newsom (U. New Mexico), and Dave Roddy (USGS)
Thursday morning, October 11: Updates and Status of Mars Exploration Program/MDAP.
Nadine Barlow provided copies of the minutes of the previous year’s meeting (Oct. 10-11, 2000) and reprints of the Consortium’s JGR paper which was published in November, 2000.
Joe Boyce provided an update on the NASA budget for the upcoming year. Although still under a continuing resolution regarding the budget, funding for the Mars Program continues to be a high priority among NASA, Congress, and the White House. There should be enough money to continue to fund the current MDAP investigations and there may be more, so Joe encouraged everyone to propose. The MDAP Review Panel will meet in November in Washington DC and notifications are to be made around late January 2002.
NASA HQ is advertising for a civil service Mars scientist position. Also, Joe announced that he is planning to retire from HQ on March 31, after which he will be joining the University of Hawaii.
Joe also noted that the grant which funds the consortium activities is running out and needs to be renewed. Our activities are currently funded under a grant to USGS (Ken Tanaka, PI). The new proposal should include upcoming workshops and conferences, specifically the possibility of organizing a conference similar to the one on “Impact and Explosion Cratering” which was organized in 1976 by Dave Roddy. Dave commented that people employed by the defense industry are very interested in revisiting this workshop. They are currently conducting many studies related to smaller non-nuclear explosions but are still interested in larger cratering events, particularly for their effects on the evolution of life. We still need to understand the mechanisms of cratering and the formation of particular material (as Dave pointed out, note the amount of particulate material created by the collapse of the World Trade Center buildings on Sept. 11). The mechanisms by which such particulate material is injected into the atmosphere and how it then spreads across large regions or the entire globe is of interest to many people. Horton Newsom noted that people at UNM are working on many aspects of this problem. But the biggest hurdle to getting a consortium of these people together is the fact that this problem crosses many disciplines and thus there are many different sources of funding. The result is that people in one area are unaware of what other groups are doing.
Joe noted that Jim Garvin has managed to get $2 million allocated to the Mars Program for terrestrial analog studies (the Mars Fundamental Research Program). This might be a good place to start in terms of bringing people together to study the effects of large impact cratering. Horton praised this initiative and noted that the direction of work done at the National Labs depends heavily on which programs have good funding sources.
Dave commented that to pull together a good consortium of people involved in cratering studies that we really need hard-ball players (like Gene Shoemaker was) to convince the various agencies that this type of work deserves to be funded. We need to get people from various disciplines together to address these issues. Dave suggested we form a committee to organize this and get things started. Joe agreed that unless there is a strong driving force behind this effort, it will not be considered by funding agencies. It will take a series of steps to accomplish our goal, but this meeting is a good place to start.
Dave noted that part of the trouble is that no one has provided a good definition of the problem, what still needs to be resolved, and the steps that might lead in that direction. We need to lobby key people in all the related disciplines so we can get people at places like the National Academy of Sciences to see the problem and lend their support. Joe noted that if we plan to use Mars money to support such an initiative/conference, it must be connected to Mars. All agreed that we could easily focus a conference on large cratering events with specific emphasis on Mars. We all agreed that what we need now is to get the interest going to support this initiative and that interest is what will drive the various funding agencies to provide the money.
Dave recommended that we identify 3 to 5 people who can constitute a lobbying community. The members of this committee should be scientists of stature in the cratering community so they will attract the attention of other scientists as well as the managers who make the decisions about funding. Dave also recommended that we do not do another 1976 symposium in exactly the same way—with the advances in technology, he suggested we could, for example, produce a virtual book on the Internet which could be constantly updated as new advances occur.
Horton noted that we need financial support to cover the travel expenses of invited speakers. We may also want to consider that any series of workshops/conferences include a number of international venues. Joe noted that Congress has added money to the NASA budget for Near Earth Asteroid studies, indicating that Congress is interested in studies of the impact threat. The fact that large impact events affect so many different areas (such as exobiology, NEA studies, etc.) might be the “catch” we need to get different offices at NASA to jump on our bandwagon—any area seen as important is the area that generates money.
Ken Tanaka provided a status report on the USGS geologic mapping of the Martian northern plains. Ken noted that Noachian-aged material on Mars is broken up, fine grained, weak material which is very easily eroded. This is probably the result of the high impact cratering rates sustained during the Noachian period. This is most easily seen along the basin edges. Volatility (especially due to CO2) may also help in the collapse process. The volumes of eroded rocks are estimated to range from 1.1 x 104 km3 for the Elysium region to 3.6 x 106 km3 in Valles Marineris. The amount of eroded rocks from the Grand Canyon is estimated at ~5 x 103 km3, for comparison.
In the South polar region we see areas apparently formed by flow. Is this due to interactions of volcanism with volatiles? The putative eskers may actually be channel-produced instead of glacial features. This is suggested by the fact that some of the “eskers” go over other ridges. Instead of forming in glaciers, these features might have formed when a thicker mantle existed which covered the ridges.
In the northern plains, Ken’s group is seeing areas with similar features. There is no sign of the shorelines proposed by Tim Parker—instead, Ken is seeing structural control, even for Contact 2. Ken’s interpretation is that the highlands-plains boundary has undergone a series of collapses, controlled perhaps by volatile concentrations. Ken noted that liquid CO2 at 0°C can lift material 450 m simply due to vapor pressure. So instead of oceans, perhaps we are seeing the remains of a series of collapses along the dichotomy boundary. Stealth craters may actually be relaxed craters instead of resulting from burial. Polygonal terrain is often found in association with the collapsed terrain.
Thursday morning: More Discussion about Conferences.
Following Ken’s update, we returned to the question about the logistics of holding a conference dedicated to large impact cratering events. The group agreed with Dave’s earlier recommendation to pull together a group of high-visibility professionals to form a lobbying committee. We need to focus on the theme of the conference (mechanisms of large craters versus a focus on Mars). The proceedings of the conference could be available on-line as a USGS open file report. Funding will be sought specifically from NSF and NASA. We also discussed how to best relate Mars (so we can get NASA Mars funding) to Earth—possibilities include the fact that there is much new information that has been learned about cratering and its effects on the Earth and its biosphere, that new databases exist of craters on Mars, the moon, and the asteroids, and there is a heightened interest in understanding the properties and dynamics of Near Earth Asteroids. The group noted that there are other conferences related to impact cratering that are being planned (specifically in England and Scandinavia), but none of them are focused on the global implications of large impacts. The plan of action agreed upon by the group is that this consortium start things off by defining the problem, followed by holding the conference and then identifying a lobby committee to meet with researchers and eventually funding agencies.
Horton Newsom reviewed the work that his group is doing on hydrothermal activity produced by the heating associated with crater formation. They have overlaid MOLA data onto the MDIMs to get accurate diameters of craters by fitting a variety of ellipses to the results. The major and minor axis, as well as the crater orientation, is available for inclusion in future crater databases. This work is producing a catalog of large craters and basins which sill be useful for analysis of the Mars Odyssey GRS data once it is acquired. What Horton and his group have found is that many previous lists of large impact structures do not correlate with features seen in the MOLA data. They have confirmed 36 craters >360 km in diameter and have identified another 4 craters which previously have not been noted.
Nimmo and Gilmore (JGR, 106, 2001) have found that many basins have low integrated magnetic field strengths (B), while smaller craters have higher B values. Horton suggested that we could possibly use data such as these to confirm or deny the existence of suspected basins. Identification and classification of craters is one of the issues Horton and his group are looking at.
Some process is apparently making the edges of the crater floor weak enough so moats form around the inner edge. Horton suspects it could be hydrothermal alteration or perhaps shock fracturing. Or perhaps the central plateau of the crater floor becomes armored with impact melt, thus making it more resistant to erosion.
Issues related to large basins:
1) Large structures need to be identified and validated. What is the best way to do this? Use of MOLA data to identify the ring diameters is probably the best method. The use of other data sets, such as the magnetic data noted above, could be a useful means to confirm suspected basins.
2) Morphology issues—how do we note the features associated with these large craters, such as the ring furrow craters? Can magnetic and gravity data provide useful techniques for classification?
3) How do we classify degraded craters? Dave noted that there is a universal progression from fresh to degraded craters seen on all bodies. But this progression depends to some extent on whether the crater is simple or complex, and if complex it depends on the definition of transient crater. The generally accepted definition of transient crater is the maximum expansion of the crater prior to wall collapse. But it is difficult to determine the energies involved in the crater formation process without understanding the transient crater.
4) How is ejecta produced and distributed during basin impacts? How does it affect life? What is the grain size distribution? Dave noted there is an incredible amount of dust produced during explosions. Sue Kieffer’s work found that 20-ton explosions on alluvium produce large amounts of glass, and of course tektites can be produced by such large impacts. Nadine noted that one explanation for the Libyan Desert Glass is that it resulted from an impact into thick sand deposits. Horton noted that the amount of glass produced by an impact is important since glass interacts with water and can affect the types of hydrothermal products. Joe wondered if the layered deposits seen on Mars could consist of fine grained material produced by these large impacts. Dave replied that explosions in dry material produce a large debris cloud—their experiments found that such a cloud can last at least 30 minutes and travels a long distance from the explosion site. They actually flew through one such debris cloud and basically were unable to see anything.
5) Is there such a thing as a pristine crater morphology on Mars? Joe said that Garvin and Malin have looked for such a pristine morphology and have not been able to find one. Hence it will be difficult to determine how much degradation craters have undergone since we do not exactly know their original characteristics.
Dave noted that much of the good information about crater excavation was DoD classified work—he and his colleagues are still working to get some of this information declassified.
At this point, the group realized that perhaps we are biting off an awful big slab of still-to-be-answered questions about cratering. We decided we needed to focus on a few important issues at this time. Joe noted that as long as Dan Goldin is NASA Administrator, life will continue to be a major focus for NASA. Obviously Mars can give us a lot of relevant information to understanding impacts on the Earth and how they can affect the evolution of life.
This led back to discussion of the focus for the conference. Do we want to focus on the huge civilization-ending type of impacts or on the smaller but just as deadly tsunami-triggering events. The latter might be politically easier to sell since it could happen on a shorter time scale.
It was agreed that all of us will write up a half-page discussion for the proposal to fund the conference. These reports will be submitted to Joe, who will write the proposal. Suggestions of people to invite to participate/organize the conference include Mark Boslough, David Crawford, Jay Melosh, Mark Cintala, Fred Horz, Bill Bottke (studies orbit evolution; SWRI), and Robert Henry (studies ejecta formation; Kirkland AFB, NM). This consortium will take the lead in identifying an organizing committee of about 10 people. We will see if LPI can provide the conference logistics. Venues suggested include NAU or UNM (so we can get graduate student help). Possible donors to help cover travel expenses for invited speakers and students include the Barringer family and Bill Hartmann. If the conference could be one of the LPI Core Workshops, expenses for the logistical support would be covered by their operations grant. Joe noted that most conferences cost about $15K, so being one of the LPI Core Workshop would help us keep expenses low. Dave estimated that travel alone could run as much as $32K. If we follow up with a virtual (on-line) proceedings volume, we can also keep costs down.
Trent Hare gave the group a demonstration of some of the new techniques the USGS is developing for analysis of MOC imagery. When we reconvened to discuss issues related to the crater databases. One of the issues raised last year was the difficulty in comparing the current crater databases (those of Barlow, Boyce, Kuzmin, and Roddy) with new MGS data because of the offset between the Viking MDIMs and the MOLA-based control net. Trent suggested that we continue to hold off on addressing this issue until USGS gets the MDIM’s correlated with the new control net. Horton suggested that we could get students to help, if additional people-power is needed.
Joe brought up the issue of ejecta morphologies and the fact that (as pointed out by Susan Sakimoto and Jim Garvin at last year’s meeting) MOLA results indicate that all layered ejecta morphologies seem to exhibit a distal rampart. Joe argued that the ramparts are telling us that liquid is present, particularly since such rampart ejecta blankets are seen around smaller craters in the same areas as the near-surface gullies reported by Malin and Edgett. Changes in the geothermal gradient with time could explain the latitudinal variations in onset diameter that Joe is seeing.
Dave noted that codes work well at describing ejecta formation and emplacement for small impacts. But for 1000-km-sized craters, the ejecta falls back into the crater instead of being ejected outside of the crater. The codes basically are unable to deal with 1000-km-sized craters. In some cases, like Steinheim, subsurface layers are not disrupted. This is completely at odds with what the codes predict. Geologic analysis suggests a highly disrupted central region but there is no indication of a bowl-shaped structure that served as the transient crater. Apparently some sort of modification is needed for the codes. Horton noted that modeling (such as that done by O’Keefe and Ahrens) is doing a good job of predicting the uplift of basement rocks. Joe noted that the computer codes are all based on shock wave propagation—perhaps something else is going on.
Trent is continuing to work on combining the various crater databases, removing duplicate information, and producing a single database with all the data. We need to include the new nomenclature, as described in the consortium JGR paper—Nadine said she is working on that as part of her crater catalog updates. Trent will work on centering Nadine’s database with MDIM 2.1 and eventually MDIM 3.
Horton suggested that the consortium collaborate on a paper describing how to identify basins based on various criteria (such as magnetic and topographic data as well as morphologic information). All agreed this was a good idea. Trent noted that he can provide many of the tools he has been working on which combine the MOLA and MDIM data. Dave and Nadine will provide lobateness (i.e., sinuosity) data to see how it compares.
Horton would like to collect information about the thicknesses and other characteristics of the layered material we are seeing on Mars. Can we get access to other databases (such as MOLA roughness, magnetic, etc.) to combine with the crater database? There was some discussion about people who do not want to release their processed data, making it difficult for others to use that data for other studies. All agreed this is very frustrating, but Trent noted that USGS eventually WILL get all those databases so we will get access eventually. MDIM-3 (Kirk) will also provide stereo views of features, which will be very useful in any analyses. MDIM 2.0 often has about a 3 km offset from the MOLA-based control net, which MDIM 2.1 will eliminate. MDIM 2.1 is in software development and is expected to be available next year sometime. It is tied to the MOLA data and provides 100 m resolution. It will be a complete redesign from previous MDIMs—there will be fewer files and bigger projections. The planetographic data sets will be replaced with planetocentric data sets by adding in the MOLA data. High-resolution MOLA data is being created specifically to allow good correlation with MDIM 3.
The big focus for the next year will be on future workshops and conferences. After additional discussion, the group agreed to focus the proposed crater conference on martian cratering for now. This conference will cover crater paleolakes, ejecta morphologies and formation, etc. The terrestrial cratering community will be encouraged to participate and provide their insights. A later conference will be devoted to large terrestrial impact events. Conferences will include not only the regular scientific sessions but we will also try to hold them in locations where we can include field trips. GIS demonstrations would also be an important addition.
The meeting adjourned at noon on Friday, October 12, 2001.