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.
Pros:
·
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.
Cons:
·
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.
The
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
Pros:
·
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
Cons:
·
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.