MINUTES OF MARS CRATER CONSORTIUM MEETING
1. Contents of Databases:
Jeff Kargel described his database of lobateness (sinuosity) information for selected craters with fluidized ejecta blankets. The data set includes quantitative measurements of ejecta blanket perimeter and area as well as crater diameter. Database was collected to address the question of how the sinuosity of fluidized ejecta patterns varies with latitude.
Nadine Barlow described her dataset of 42,283 craters >5-km-diameter distributed across the entire planet. The database includes information on crater location, size, terrain, basic preservational category, ejecta and interior structures, elliptical crater data, central pit diameter, and comments (crater name; comments about quality of imagery which could affect interpretation, etc.). The database was collected primarily to conduct crater size-frequency distribution analysis to revise the martian relative chronology.
David Roddy described the database that he and Nancy Isbell developed. The database contains morphometric data on over 4300 martian impact craters. The included craters displayed one or more of the following: minimally degraded crater at least 10 km in diameter, an ejecta blanket, central peak(s), central pit(s) in central peaks, secondary ejecta field(s), pedestal/rampart features, multirings, or an unusual morphologic feature. The data were collected to address crater mechanical questions on the formation of martian impact craters.
David Roddy also showed data provided by Jim Garvin. Garvin is producing a database of martian impact crater topographic profiles derived from MOLA data. The database provides the first detailed information on crater rim heights, crater depths, central peak heights and widths, central pit diameters and depths, ejecta blanket thicknesses, etc.
James Dohm spoke about the crater data that he, Ken Tanaka, and Juan Lias collected during their study of the tectonic evolution of Thaumasia. The crater data were collected primarily to determine age relationships between different units.
Jennifer (Fred) Ramstad spoke briefly about the study she is initiating on the study of onset diameters for craters displaying fluidized ejecta patterns.
2. Other Inventories
Participants identified other databases which should be included in the consortium archives. These included the crater lake database of Natalie Cabrol and the fluidized ejecta crater database of Francois Costard.
3. Testing of Databases (using ArcInfo)
David Roddy’s and Nadine Barlow’s databases have been incorporated into ArcInfo and ArcView by Trent Hare. Hare provided a demonstration of the capabilities of ArcInfo using the two databases. ArcInfo provides the means to perform multiparameter interactive comparisons and to compare results between the two datasets. Results of comparisons between the two datasets are generally consistent. The differences observed are likely the result of the different emphases of the two databases (i.e., Roddy’s database is more geographically and morphologically limited, while the ejecta/interior classifications in Barlow’s database are not complete). Roddy and Barlow agreed to work on standardizing their datasets and recompare. All agreed that ArcInfo is a powerful tool to compare and extract information from databases and holds great promise for a number of studies about the distribution of specific impact crater characteristics.
4. Workshop Discussion
The goal of the planned workshop is to bring together Mars crater researchers to address the following issues:
· Standardization of procedures and nomenclature
· Recommend standards for data format
· Determine where such databases should be archived for access by the community (a web site maintained by the USGS was recommended)
· Review what types of databases exist and why they were collected
· Determine what kinds of crater data exist or are needed to address major questions about Mars, such as its crater history, its erosional history, its volatile inventory, and its crustal properties
Participants agreed that the workshop should include a demonstration of the capabilities of ArcInfo and ArcView, as well as overview talks (suggested topics were the geology of Mars, erosional history, crater mechanics, and Joe’s perspective on the status of our knowledge and what current/future missions will likely provide).
The biggest discussion was where and when to hold the workshop. One suggestion was to hold it in conjunction with the Lunar and Planetary Science Conference.
· People will be coming to the meeting anyway so they will not have to try to find extra travel funds
· Computing facilities for an ArcInfo demonstration are readily available through LPI.
· The workshop will be competing with many other workshops held in conjunction with LPSC
· We would likely draw a larger group of people, including many not directly involved in database collection, taking away from the desired atmosphere of making this a small working meeting.
other suggestion was to hold it in conjunction with a Mars mission launch such
as the Mars Surveyor 98 launches (particularly the December launch). The workshop itself would be held in
· Many people may be going to the launch anyway, or be interested in attending so the meeting will add extra incentive
· Can be the desired small group
· Will not be distracted by the activities of LPSC or other concurrent workshops
· Unless they are already attending the launch, people would have to find extra travel funds to attend
· Expenses associated with renting a room for the meeting may be higher than at LPI and computer facilities may not be as accessible as at LPI (Barlow will check into these issues).
· Short turn-around time from the funding request (to Mars DAP) to the time of the proposed workshop.
Consortium members decided to identify people who would be interested in the workshop and e-mail them for information on (a) their interest and (b) their preferred location and date.
5. Formatting and Storage/Access
The group was impressed by the demonstrated capabilities of ArcInfo and ArcView and strongly supported the use of this system for the archiving and access of impact crater databases. The drawbacks include the expense of the software and the system requirements needed to run the software. In addition, someone needs to be sufficiently familiar with the program to be able to input the data in the proper format and manipulate the program to get the desired multiparameter results. There is concern that probably only a few locations could afford the system.
The group recommended that the databases be archived at the USGS with access through a Web site.
6. Web Sites—see #5
7. Summarize Future Planes/Recommendations
Workshop: Bob Craddock, Joe Boyce, and Nadine Barlow will poll the community and organize the workshop. Chuck Barnes will help with e-mailing information.
Recommendations of the group: The goals of this consortium and the workshop (to inform the community of available databases, to recommend standards for the nomenclature and format of such databases, and to make recommendations on the archiving of such databases) are strongly endorsed by this group. We recommend continuation and expansion of this Martian Impact Crater Consortium.
8. Consortium Development/Expansion
Roddy, Boyce, Barlow, and Craddock will identify other potential consortium members.
9. Reviewed Archives
At this meeting, Roddy and Barlow compared their datasets using ArcInfo as well as going back to the original photomosaics and overlays. They agreed on each other’s interpretation and nomenclature of crater features. In addition, Boyce, Roddy, Barlow, and Barnes met with Ramstad to answer questions she had about her fluidized crater onset diameter project.
10. Software Selection
Group recommended use of ArcInfo, recognizing that individuals will use other software that meets their particular needs. Trent Hare (and his successors) will provide ArcInfo formatting requirements to researchers so their databases can be easily incorporated. The Consortium will be open to suggestions of other software products that come to our attention.
11. Science Discussion
The science discussion focused on how Martian impact crater databases can be used to describe the following:
a) The geologic history of Mars (from crater densities and crater size-frequency distribution analyses)
b) The distribution and physical state of subsurface volatile reservoirs (from fluidized ejecta morphologies)
c) The erosional history of Mars and processes responsible (photoclinometry versus MOLA profiles)
d) Tests to determine if the fluidized ejecta pattern is due to impact into subsurface volatiles or due to atmospheric entrainment of ejected material
e) How crustal properties affect the resulting crater morphology/morphometry.
12. Cratering Mechanics
Martian impact craters can be compared with their counterparts on other bodies (especially Earth and Moon) to test various questions related to cratering mechanics. In particular, information on crustal properties may be provided through study of impact crater morphometric information, such as depth-diameter ratios, central peak height and base width, wall terrace width, central pit diameter and type (floor versus summit pit), and ejecta blanket area and sinuosity.
13. UDIR Database
Roddy will look into acquiring a copy of this database.
14. Continued Analysis
Barlow will check completeness of and update the ejecta and interior morphology data in her Catalog. She also will provide Hare with a copy of her database on ejecta blanket lobateness.
Roddy will check the accuracy and completeness of his database of crater morphometric properties.
Ramstad will continue her analysis of the onset diameters for craters with fluidized ejecta morphologies.
Kargel will provide his lobateness data to Hare for archiving in ArcInfo.