Attending:  Nadine Barlow (Northern AZ Univ.), Jake Bleacher (AZ State Univ.),

Joe Boyce (Univ. Hawaii), Devon Burr (USGS),  Trent Hare (USGS),  Jennifer Neal (Northern AZ Univ.), Horton Newsom (Univ. NM),  Livio Tornabene (Univ. Tennessee), Shawn Wright (AZ State Univ.).


Thursday, October 9, AM

The session began with introductions and a summary of research interests/activities.  Barlow noted that the Mars Crater Consortium has been quite active this past year, including submission of an abstract to the ISPRS WG IV/9: Extraterrestrial Mapping Workshop Advances in Planetary Mapping 2003 (presentation on March 22, 2003, given by Barlow; Boyce also attended the meeting).   Much interest was generated in the Mars crater databases based on that presentation.  In addition, the Mars Crater Consortium website is now up and running at www.marscraterconsortium.nau.edu.


Mars Program updates 

MER A (Spirit) and MER B (Opportunity) were launched on June 10, 2003, and July 7, 2003, respectively and are on track for landing on Mars in January 2004.  Spirit will land in Gusev Crater while Opportunity will land in the Merdiani hematite region.  Both locations show abundant small crater populations which the rovers should be able to investigate.


Spacecraft Data:  General Discussion 

Newsom noted that much of the data that would have been useful during the MER landing site selection arrived after the decisions had been made.  It would be useful to have additional meetings now with insights from the new data.  Also, we need a place to be able to submit requests for images.  Tornabene noted that there is a program designed to do this called JMars, which is up but not always useful.  Tornabene also noted that THEMIS data continue to contain an aberration (ghost) that still needs to be taken care of.  The discussion then turned to Mars Express data—Boyce noted that there is an agreement between ESA and NASA for general release within 6 months, although he suspects that Gerhard Neukum may try to release High Resolution Stereo Camera (HRSC) data earlier to the community.  Jim Garvin (NASA) will be in charge of getting everything set up so the community can use the Mars Express data.  Newsom reminded everyone that the Mars Odyssey GRS is providing important information and that there are few scientists on the team to really look at the data.  Hare said that USGS has proposed to PGG to put the higher resolution Viking data on-line and register it to the new MOLA-based coordinates.  The toughest part of Viking data is getting it processed—it is not very user friendly.


Explosion Cratering Literature 

Participants at the 5th Mars Crater Consortium (MCC) meeting (Oct. 2002) identified the need for a bibliography of the unclassified explosion cratering literature.  Sarah Stewart (Harvard) is collecting information on these references—all suggestions should be forwarded to her.  This information will be provided on the MCC web site.


Impact Cratering: Bridging the Gap Between Modeling and Observations Workshop

Newsom and Wright reported on the February 7-9, 2003 workshop at LPI on Impact Cratering: Bridging the Gap Between Modeling and Observations.  Much of modeling does not currently replicate observed features.  Two main areas that the modelers are branching out into are inclusion of faults and atmospheric interactions.  David Crawford (Sandia) is running models with a billion cells in order to look at the passage of shock wave through grains in fine scale material (crystal/micron scale).  He finds that shock can melt grain boundaries.  On the field work side, there has been substantial progress in areas such as the Chicxulub drilling program and in discussions of nomenclature.  There is an increased effort to get detailed information from field work.  In India there is a group working on Lonar crater; unfortunately the drill cores done ~30 years ago appear to be lost.  Christian Koerbel (Univ. Vienna) has funds to drill a crater in Africa.  The meeting discussed new ideas about what happens to central peaks as they come up and then collapse—models suggest that in some situations a wave expands outward as the peak collapses.  This could explain observations at Bushveld where supertemperature melts are hard to explain unless the material temperature greatly exceeded the liquidus and melted.  Analysis of crater structures is providing more clues on central peak formation.  The workshop emphasized the need for both modeling and observations in order to understand the cratering process.


Data Analysis Tools

Hare and his USGS colleagues demonstrated the latest data analysis tools for using MOC stereo imagery.  Demonstration included a crater within Schiaparelli and etched material in Meridiani.


Hare emphasized the importance of being aware of THEMIS updates.  ISIS sends out updates, so get on the list.  For THEMIS, software gets updated more frequently than ISIS, so additional updates get sent out (separate list).  Latest release is THEMIS geometry software release 180, dated Aug 28, 2003.  To get coordinates, need spacecraft data contained in the SPICE files.  Be aware that the new release has the latest version of the SPICE files (original ones gave incorrect coordinates).  With the latest update, you need to include 3 parameters to control the coordinates so you don’t run into problems with mosaicking, etc., around longitude 0°/360°.  The update operates in ISIS.  There is a document on the ISIS website that details THEMIS geometry. VIS band to band registration sometimes is as much as a couple pixels off because the high gain antenna is twitching when pointed to Earth, which in turn wobbles the spacecraft.  IR registration may be off when mosaicking because timing can be off by up to 4 pixels.


Hare is not sure if Phil Christensen (ASU) has a plan to do global mapping yet with THEMIS.  The community needs to put pressure on him to have this done.  Boyce noted that the current plan is to systematically map the planet with IR, but we likely will not get global VIS coverage due to its higher resolution.  Newsom asked if there are any plans to put out regional mosaics.  Hare suspects it will probably have to wait until the public release of JMars (mission planning tool but also a GIS system, so it can do layering), which can now do shape models and bring in the geology.  JMars has the ability to load local data and potentially will be able to load web serve data. 


Hare is developing a number of tools to assist in crater analysis.  ArcMap 9 will include all planetary bodies.  The Mars crater database site on PIGWAD currently gets quite a few hits, but it may eventually be moved it off PIGWAD.  Hare and Barlow briefly discussed Ken Tanaka’s (USGS) Mars Fundamental Research Program proposal to provide Mars crater data and analysis tools on-line.  PIGWAD also includes a discussion group to answer questions from primarily a GIS viewpoint.  ArcMap is probably the best GIS tool right now.  ISIS uses some IDL, but IDL is very difficult to use unless you are really into programming.  Plan is to implement a metadata server this year which can easily bring up all the applicable datasets for a particular area.


Catalog of Large Martian Impact Craters, version 2.0, and MFRP Proposal

Barlow discussed the status of the revision of her Catalog of Large Martian Impact Craters.  She is using MOC, MOLA, and THEMIS data to update and extend the information for all craters larger than 5-km-diameter.  Plan is to have the revision completed by end of 2004.  Barlow will provide the revised Catalog to Hare for ingestion into PIGWAD, where it will serve as the basis for the on-line crater database. 


The Mars Express HRSC team has contacted Barlow about using the numbering system in the Catalog as the identifiers of craters on the high resolution surface maps they will be producing.  In the original version of the Catalog, numbers were assigned to craters based on MC subquadrangle and location on specific terrain units.  However, the use of the MC subquadrangles is declining and Barlow suggested that a new numbering system be utilized in the revised Catalog.  Two options:  (1) number each crater consecutively based on latitude-longitude; or (2) use a numbering system that includes the crater’s latitude and longitude coordinates (similar to catalogs of astronomical features).  Advantage of the latter technique allows craters to be identified and added later without disrupting the numbering system. 


Tanaka’s MFRP proposal consisted of two parts, one dealing with on-line access of crater databases and analysis tools.  The proposal was funded for one year, with the suggestion from Curt Niebur (NASA HQ) that the proposed study be split into two separate proposals and a new PI be responsible for one part.  Barlow has agreed to server as the PI for the MFRP proposal on continuing the development of on-line crater analysis tools and access of the crater databases.  Another suggestion on Tanaka’s proposal was to identify a group which would evaluate the developed tools and advise the PI and co-I’s on additional needs of the community.  Barlow proposed that the MCC serve as this advisory and evaluation committee and the MCC agreed.


General Discussion:

Boyce noted the need to encourage more people to attend the MCC annual meeting.  Participants suggested additional people who should be invited—Barlow asked that names and e-mails be sent to her to include on the e-mail distribution list.  Barlow will ensure that the meeting is announced in venues such as the MEPAG Mars calendar.  Another suggestion was to append the meeting to another conference, such as LPSC or AGU.  A third possibility was to move the meeting to a more easily accessible location, such as Phoenix, or to at least alternate locations.


Thursday, October 9, PM:

Research Presentations:

Sarah Stewart (Harvard) joined the discussion via telephone.


Shawn Wright:  Thermal IR Analysis and Terrestrial Impact Craters

Wright is using the ASTER imager to do thermal IR analysis of Earth, with a specific emphasis on geologic units associated with Meteor Crater (e.g., Kaibab, Coconino, and Moenkopi formations).  The problem with multispectral imaging is that the instrument only takes a certain number of points (5 for ASTER compared to 198 points for THEMIS) so all absorptions are not seen.  This also causes one to miss some small lithologic units.


Deconvolution of both THEMIS and ASTER data with image end-members provides accurate interpretations of ejecta distributions.  Sample end member spectra (EMS) often do not provide good fits.  Lithologies and mineralogies with low abundance are often missed.  Wright discussed the use of THEMIS data to analyze a 1-km-diameter fresh crater in Syrtis Major.  The THEMIS radiance was separated into temperature and emissivity and atmospheric corrections were ignored.  The crater ejecta blanket clearly shows up in the temperature view, but begins to blend into the surroundings in the emissivity view.  Image EMA suggests two end member compositions.


Results:  Lower daytime and higher nighttime temperatures imply the existence of a rocky ejecta blanket.  The ejecta blanket and the surroundings appear to be of the same material.  Rims and ejecta blankets expose bedrock—these pixels are ideal targets for deconvolution when dust mantles the surrounding region.


This study has primarily been looking at small young craters—dark in day IR, bright in night IR.  Wright is just starting to look the thermal IR (TIR) characteristics of shocked minerals.  Absorption bands are seen to vary with the degree of shock.  A future direction of this project includes using Lonar Crater samples to determine if naturally-shocked materials are different than experimentally-shocked materials.  Currently shocked materials are not included in the ASU spectral lab—need this!  Could Bandfield’s spectral types 1 and 2 be the result of shock effects?  Newsom noted that he is considering submitting a proposal to get samples from Lonar and other locations to analyze specifically for shock effects.  Unfortunately all the people who have done shock studies at Lonar (i.e., Milton, S. Kieffer) no longer have their original samples, so new samples are needed.  Newsom also noted that looking at material characteristics at different levels of shock is not straight-forward—it requires petrographic analysis, thin sections, etc.  Wright agreed and mentioned that another problem with TIR is that surface roughness, faceting, etc., can affect the absorption characteristics.


Joe Boyce:  Uses/Misuses of MOLA Data and Development

General discussion about the limitations of MOLA data.  Stewart has found a number of “bad” MOLA tracks.  Hare noted that one needs to strip off the off-nadir pointing since they are not accurate.   Stewart has been using the trigrid in IDL to get as many points as possible.  Bad tracks show up often and appear to be shifted slightly along track—look like lines/ridges, which has caused her to be dubious of any linear features.  Hare suggested taking data with track number before doing the interpolation so she can identify and eliminate bad tracks before interpolation. 


Boyce agreed that there are many pitfalls that one has to be aware of when using the data.  One needs to keep in mind the resolution of MOLA versus the resolution of the crater you are interested in—inaccuracies will “blast” you.  Don’t forget you are working with interpolated data.


Newsom asked if anyone knew the status of the MOLA-based crater morphometry paper by Garvin et al.  Boyce thought it might be in review, but was not sure.  Barlow said the last word she had heard from Susan Sakimoto (GSFC) was that funding was tight and they were not sure when it might get out. 


Boyce noted that Peter Mouginis-Mark (Univ. HI) and Bob Craddock (Smithsonian) have developed “quick” ways to produce topographic maps and get topography data, but all of these methods are slightly different.  They should produce the same results, but Boyce was not sure that they do.  He proposed to select a set of craters and compare the different techniques.  Stewart suggested that another possibility would be to construct artificial craters that we know the volumes of and then put them on terrain, run these topography programs, and see how accurate the results are.  Boyce and Mouginis-Mark will create a list of approximately one dozen craters while Craddock’s group and Garvin’s group could put together a similar list of craters, which then all the different groups could use with their techniques and compare the results.  Stewart will build up fake craters and fake MOLA tracks to provide to the others as additional tests.  Hare offered to provide similar data for Meteor Crater.  Boyce will be the contact person for collection and distribution of the data.  Boyce will obtain the crater lists from the other groups, Stewart will provide the artificial craters, and Hare will put everything on his web site for access.  Timeline:  done before LPSC—maybe in time for abstracts?  Stewart expects there will be consistency for large crater D, but more divergence for smaller craters.  Question is where the transition diameter is. 


Shock Effects

Stewart is interested in studying the shock effects on magnetization of basalt.  Newsom offered to provide samples from Lonar Crater in India.  Stewart and her colleagues are trying to correlate the peak pressure of shock with changes in magnetic susceptibility.  Magnetic measurements are a finer determinant of temperature. 


Sarah Stewart—New Gun Lab at Harvard

Stewart reported that the new impact crater research facilities are almost ready at Harvard.  They have the gun set up and were expecting to conduct the first shots the next weekend.  The first project using the facilities will be looking at the shock Hugoniots of ices and ice-rich samples.  They will include embedded gauges to obtain information such as particle velocities and shock pressures.  They are also building in a cooling system to enable studies looking at the effective temperature of volatile releases, etc.  Stewart is also interested in the effect of strain rate on phase transformation during shock.  In natural impacts, pressure rise time is longer than in experiments, so she is interested in looking at actual transformation properties.  Stewart has hired a lab manager with shock wave experience and thus things have progressed faster than expected.   


Trent Hare—Photoclinometry using THEMIS (“Magic Airbrush Technique”)

Hare is working with Larry Soderblom (USGS) to derive a photoclinometric technique using THEMIS data.  How do you do photoclinometry on something that doesn’t really show a shadow?  MOC has a lot of constraints on images before photoclinometry can work—THEMIS may not have as much.  As a side note, Randy Kirk is about to release his photoclinometry code on ISIS which will make photoclinometry easier to use. 


The technique inputs THEMIS IR (night and day), THEMIS VIS, and MOLA.  VIS contains albedo and slope information.  Day IR contains some albedo data and night IR is a proxy for albedo without the slope component.  One can subtract out the thermal inertia as a single layer and extract the albedo component.  Subtracting out the albedo component gives the topographic shading component.  Combining that with MOLA allows one to derive an elevation model.  The downside is the technique is limited to the resolution of the IR (~100 m/pixel) and one has to degrade the VIS data to IR resolution.  This THEMIS photoclinometry technique shows finer detail than MOLA provides.  But a problem with the technique is coverage—have to have IR (day and night), VIS, and MOLA covering the same area.  Soderblom’s goal is to make it easy enough to be able to use it on smaller computers, maybe even personal computers, but that depends on if a PC version of ISIS is developed.


Group agrees that we need these “tertiary” data products available where processing has been done by the experts who then provide the finished product to community.  Will still need to do a few little “tweaks” to register everything properly, but should otherwise be “plug and play”.


One of the advantages of the MCC meeting is the ability to learn about these new data analysis techniques.  Hare noted that one of the big missing parts of LPSC is the lack of technology presentations.  The Advances in Planetary Mapping workshop this last year helped fill that void, but it is not held every year.  Newsom suggested that Stephen Mackwell, the new LPI director, would likely be very receptive to having a special session after LPSC or as an evening session.  Randy Kirk was suggested as someone who might be interested in helping to organize such a session.


Mars Crater Workshop Discussion (led by Boyce)

The MCC has discussed for several years the possibility of organizing a community workshop to discuss martian impact craters.  We recognize that a good understanding of what crater morphology is telling us is dependent on understanding crater mechanics.  The two areas feed into each other.  MCC should be the driving force for a workshop/conference ala David Roddy’s 1976 conference on impact and explosion cratering, which included computational, experimental, and field geologic studies.  We see many interesting features in impact craters on planetary surfaces but have no idea how they formed.  We need to get the input of the computer modelers.  Newsom will contact Crawford at Sandia to see if we can get interest among the defense/experimental people.  There are also many studies of what is going on with small terrestrial craters, which would also be applicable to Mars.  Other possible people to talk to:  Jay Melosh (Univ. AZ), Tom Ahrens (CalTech). 


This workshop would have similar objectives to the February 2003 Impact Cratering workshop at LPI.  Newsom and Wright both felt that workshop was good but had some limitations.  The big thing the organizers did at that meeting was to bring in people doing field work to talk with the modelers.  But often the field people ignore the physics of what is going on.  Our workshop would focus more specifically on applications to Mars, but there are many areas of overlap.  For example, people are trying to understand KT ejecta in terms of the global distribution of ejecta due to rotation—Sarah Stewart and Pete Schultz (Brown Univ.) are doing similar studies for Mars.  We will contact Robbie Herrick (LPI) about combining future workshops with ours.  Boyce suggested that we need a conference focusing on ejecta, especially layered ejecta morphologies.


Possible topics for the workshop:

1)      The role of volatiles in impact cratering.  Effect of impact into volatile-rich material.  Hydrothermal alteration.   

2)      Large craters and basins (focus on ejecta?).  Cataclysmic bombardment vs resetting of crater ages by most recent large impacts.  Possible tie-in with the Large Meteorite Impacts series of meetings (most recently in August 2003 at the Ries Crater in Germnay).


Participants expressed a preference for topic 1 on the role of volatiles in impact cratering.


Friday, October 10, AM

Research Presentations:


Jake Bleacher—Pedestal Craters

Bleacher is using MOLA profiles to determine the topography of craters.  He finds that pedestal crater ejecta appear to be thicker than typical lunar ejecta.  But when compared with other martian craters, they are not much thicker.  The most commonly proposed origin for pedestal craters is post-impact modification.  Arguments against post-impact modification include symmetric pedestals, preserved ejecta ramparts, fresh undegraded ejecta blankets, interactions between pedestals, preserved secondary crater fields.


Barlow and Newsom as well as Bleacher all noted that pedestal craters tend to be found in friable materials where volatiles are believed to be concentrated (polar regions, Gusev, Arabia).


Study area:  Dorsa Argentea region (72-79°S, 230-275°E), Dorsa Argentea Formation (DAF), Parva Member (Tanaka and Kolb, 2001).  The region is adjacent to the south polar deposits, cratered terrain, and the Cavi Member.  Parva Member features:  relatively smooth surface, regional topographic low, three crater forms (fresh craters, pedestal craters, subdued or ghost craters), sinuous ridges.



1)      Pedestal craters adhere to post impact modification theory.

2)      Pedestal crater presence suggests burial and subsequent erosion

3)      Supported by presence of ghost craters

4)      Crater counts indicate Hesperian surface covering Noachian terrain


Burr noted that many of the secondary craters they have mapped show pedestals.  Boyce cautioned about using Neukum cratering curves.  Eg:  onset diameter of fluidized craters creates a bump in the curve and that varies depending on location.  Barlow also pointed out that Neukum’s production curves are based on young volcanic surfaces—there may be changes in the production populations over time.


Bleacher calculated the debris mantle thickness using the ghost-crater technique of DeHon (1974) and came up with a result that the debris mantle is <400 m thick.  Thickness estimate is a maximum as ghost crater rims have likely undergone erosion.  Mantle is deepest to the east, adjacent to the Cavi Member.  If mantle is <400 m thick, pedestal crater impact would have been deep enough to penetrate the overlying mantle.


Bleacher is estimating erosion rates by using the tallest pedestal to estimate the amount of topography lost.  Parva Member is of early to late Hesperian.  Bleacher is using the crater age curves of Hartmann and Neukum (2001) to calculate erosion rates.  Must calculate a range since the actual period of erosion is undetermined.  Hesperian to present:  ~10-7 m/yr.  These erosion rates are within the published range of 10-5 to 10-8.  Head and Pratt (2001) suggested that the region is a remnant unit caused by extensive meltback of  volatiles.  Tanaka and Kolb (2001) alternately suggest that the region was eroded by volcani-clastic slurries.  Both interpretations require regional deflation.


Observations:  Highest pedestal is the same elevation as the Dorsa Member.  Rough Cavi Member overlies Dorsa.  Larger neighboring craters show significant floor deposition.  Parva Member smoothly transitions into polar layered deposits.


Conclusions:  Parva Member pedestal craters likely formed by post impact modification.  Craters suggest regional deflation occurred with <400 m of mantle material remaining.  Pedestal craters used to estimate erosion rates of 1.3 x 10-7 to 5.2 x 10-7 m/yr.  Surface preserved in tallest pedestal is likely an extension of the adjacent DAF deposits.  Parva may have originally been a volatile-rich polar deposit not protected beneath volcani-clasitic deposits.


This study was published in JGR Planets in July.


Horton Newsom—Meridiani Impact Basin

Newsom has identified a large impact crater in the Meridiani region of Mars which appears to be associated with channels and lacustrine basins in the area and may help explain the hematite deposits.  Main points:  A large early multiringed impact basin underlies southern Arabia and Meridiani Planum region.  The hematite is the top of a layered sequence of rocks that were deposited very early.  The analysis suggests an abundance of surface water relatively recently.  Outer ring fault ~600-800 km diameter and rim crest 380 km (+/- 56 km) diameter.  Newsom and his group are using GIS tools to do the analysis.


Multiring basin is possibly 1600 km diameter, as seen in detrended MOLA topography.  Trough between inner and outer rings seems to control the flow of channels in the area.  Also see a large negative magnetic anomaly near center of proposed basin.  Newsom is collecting evidence that the basin predates the layered deposits, primarily from observations of channels in the center of the basin being exhumed from under the layered deposits (seen in THEMIS VIS—MOC tends to miss a lot of these areas).


Could hydrothermal processes associated with the basin play a role in the formation of the Meridiani hematite deposit?  Impact melt is probably less likely than a volcanic ash origin.  Strongest hematite signature is near the largest basin.  See evidence for drainage from the 150-km-diameter crater in THEMIS and MOC imagery.  There is some possible evidence for shorelines.  New data show evidence for recent fluvial activity.  Also see evidence for interaction of flow with the multiple-layer ejecta of a 20 km crater.  Southern basin “watershed” would cover an area the size of Texas.  Parker and Edgett first saw the layered deposits in this area.  Those layered deposits are within the basin floor, so they could be ancient (Noachian?) sedimentary deposits.   GRS data also suggests the presence of volatile-rich surface material.


General feeling:  This is an area where we can see the influence of water over the past 4 BY.  Water has affected this area throughout its history.


Tornabene asked if gravity data indicated the presence of the basin.  Newsom said they looked at the gravity data but no signature is detected over this area.  Could simply be due to the age of the basin.


Randy Kirk—Mars Express High-Resolution Stereo Camera

Basic resolution of the camera is 10 m.  The team plans to make elevation models and high-resolution maps (1:200,000 scale; possibly 1:000,000 scale, etc.).  The biggest problem is trying to find something to be able to label features on maps.  Proposal:  Put crater numbers on maps. 

How soon?  Start making maps in 2004.  Estimates 10-50 quads a year.  Only a subset would be hardcopy; most would be electronic.  Probably mid-2004.  Can we renumber before they start producing maps. Intensive effort at beginning of mission to focus on Beagle landing site. But elliptical orbit, so will largely focus high-resolution mapping on Southern Hemisphere initially.

Barlow noted that the consensus of group from the day before would be to renumber globally, using latitude/longitude.  Barlow will go ahead and focus her efforts on simply updating latitude and longitude now and go back later to do revision of classifications.


Kirk also noted that MDIM 2.1 is the best we can do with Viking data.  Looking ahead we may have MDIM 3.0 based on MOC; MDIM 4.0 based on THEMIS, etc.  By end of the Mars Odyssey mission we should have global IR and less than global VIS.  Magic Airbrush technique gets you to 100 m resolution in topography.  HRSC will be better, but could be courser.  Both are complementary but also very computationally intensive.  Kirk felt it would be big project to provide the Magic Airbrush technique to the community in an easy-to-use form.


Devon Burr:  Crater Counts in Cerberus Plains

Burr and colleagues looked at 3 channels:  Athabasca, Marte, and an unnamed channel to the NE of Athabasca.  They counted craters on the channel floors using MOC, particularly on the striated terrain.  They tried to pick regions that were not too dusty.  Marte Valles is difficult because it is embayed by what appear to be lava flows (others suggest these are debris flows/lahars).  On Marte, Burr counted craters on both the putative lava flows and the channel floor not covered by the dark material and came up with similar crater densities.  Similar crater-density terrain occurs to the north where rootless cones are found, which are likely another indication of the interaction of water and volcanism—lava overrunning volatile-rich (saturated?) substrate, causing steam explosions.  Craters follow the isochrones nicely up to about 20 m diameter, where they turn over (due to dust infill? Volcanic?).  However, the group now believes that many of the craters of this size may be secondaries from a 10-km-diameter crater tentatively named Zunil (McEwen et al., 2003).


This raised the question of how much of the small crater record is the result of secondary cratering.  Boyce suggested that Shoemaker was probably right in that lunar craters <1 km are dominated by secondaries.  Many are high velocity secondaries which will not be distinguished from primaries.  Burr noted that her work shows a break in the size-frequency distribution curve at ~1 km.  McEwen narrowed this down as largely secondaries from Zunil.  Barlow noted that a big unresolved question of great interest to crater statistical studies is whether secondary production is the same on the Moon and Mars.  Boyce noted that another question is whether the distribution of secondaries is uniform around globe.  Burr replied that Bob Strom sees small ray craters everywhere, which are interpreted to be primary impacts.  Barlow asked if this was necessarily an indication of a primary impact.  Boyce stated that high velocity secondaries as well as primaries would be expected to look like this.  Barlow also questioned what role the target material plays in secondary production.  Burr said one of the interesting results of her study is that long secondary rays are not seen on Marte Valles, which is expected to be of similar material to that on which Zunil is found.  Barlow suggested that meteorite velocity might also play a role (i.e., cometary vs asteroid).


Burr also discussed how the young age of Zunil might make it a candidate source crater for some of the SNC meteorites.  Mineralogic data from THEMIS could help, but unfortunately Athabasca is largely dust covered.  Tornabene noted that this is one of the problems he is interested in pursuing and suggested using locations where bedrock is exposed, such as crater rims/walls.  Newsom reminded everyone that crater rims and walls are not the only dust-free location—scarps, for example, might also be locations which are not dust-covered. 


Conclusions from Burr’s study:  Crater counting in conjunction with geologic and topographic evidence indicates the 3 channels are distinct and formed at 3 different times.  Athabasca and Marte are separated by a ridge—probably could not get water through this ridge in sufficient volumes to carve Marte.  Proposed formation ages of the channels:  Athabascia:  2-8 MA; Unnamed:  10-40 Ma;  Marte: 35-140 Ma.


Boyce suggested that Burr might check the MOC based curves with Viking to see if the smaller crater curve connects with larger crater curve or if there is some sort of disconnect.  Barlow also suggested checking to see if there is THEMIS VIS in this area that could serve as a connection between MOC and Viking resolutions.  Newsom recommended doing a student-T test to determine if the channels really retain distinct crater populations.


Open Discussion:

Abstracts:  Following the recommendation from last year’s MCC meeting, we required abstracts for this year’s meeting.  Barlow collected the abstracts and made them accessible through the MCC web site.  There was a suggestion of compiling the abstracts into a USGS Open Report.  Hare will look into this, but noted that abstracts would need to be peer-reviewed in this case.  Another option is to keep them on-line and add an abstract number, which would make them accessible for on-line search engines—Barlow agreed to do this.  Newsom suggested we also include keywords which would make it easier to search.


Explosion Cratering Literature:  Newsom raised the question about copyrights for the explosion cratering literature.  Could we scan the literature and put it on-line for easier access?


MCC WebSite:  Wright suggested we provide a link on MCC participant names that can take people to participant home webpages.


MCC Meeting and Crater Workshop: 

How do we encourage more participation at the MCC meeting?  Barlow asked everyone to send her the names of people who should be invited to the meeting.  Newsom suggested that the Barringers might be willing to provide some financial assistance for travel.  What types of incentives can we provide for getting people to attend?  Honoraria for special presentations?  Field trip to the floor of Meteor Crater?


Boyce noted that we need to have funding to help support keynote speaker travel for the Mars Crater Workshop.  Would need to propose to NASA Mars Program for this workshop and see if Garvin will provide some funding.  Much of support can be provided by LPI (Paul Schenk, Robbie Herrick, and Steve Clifford could be local contacts). 


Barlow raised the question of whether we still need the MCC meeting if we have a full workshop devoted to martian impact craters.  Boyce argued yes, since the MCC meeting discusses different issues like databases, data analysis tools, etc.  Barlow then asked whether the MCC meeting should be linked to the conference itself (before or after) or have it at a separate time (still in Flagstaff?).  Newsom plans to bring several of the Southwestern Indian Polytechnic Institute students he has been working with to next year’s MCC meeting, not only for the meeting discussions but also to be able to work with Trent Hare on GIS-related issues, so he would like to have the MCC meeting continue at USGS-Flagstaff.  Hare noted that USGS plans to develop a specific room where students/scientists can interact with USGS people for training, etc.


Boyce again emphasized that we need to strengthen the MCC and make sure that people involved in Mars crater research show up.  Newsom suggested we could tie into funding priorities for HQ.  Boyce agreed, stating that we need to show research priorities to people at HQ to enhance funding possibilities. 


Tentative timing for Crater Workshop:  Fall, 2004.  Location:  Probably Lunar and Planetary Institute in Houston, TX.  Conference Proceedings:  Special issue in a journal. 


Working title:  Role of Volatiles in Impact Cratering in the Solar System

General areas of interest:

Mechanics—role of volatiles on formation of pits and ejecta  (explosion, experiment (lab), calculation/numerical)

Morphology variations as a function of ??

Composition of volatile component—effects; concentrations

Atmosphere effects

Terrestrial field studies

Geochemical effects—effects on target materials

Effects of volatiles on crater density distributions


Organizing Committee:   

Newsom will discuss the workshop with Schenk, Herrick and Clifford before approaching Mackwell about LPI support.  Barlow will circulate above ideas to entire Mars Crater Consortium membership.  After input, we will finalize a proposal to send to LPI and NASA. 



 Meeting adjourned at approximately 12 noon.