SECOND ANNOUNCEMENT – NOVEMBER 2000

Dear Colleagues:

We are writing to remind you that abstracts for the First Landing Site Workshop for the 2003 Mars Exploration Rovers (MER-A and MER-B) are due on December 8, 2000, by 5:00 p.m. CST (no exceptions!). The workshop will be held January 24–25, 2001, at the NASA Ames Research Center in Mountain View, California. Foreign nationals who wish to attend the workshop must contact local organizer Ginny Gulick (vgulick@mail.arc.nasa.gov) no later than December 11, 2000, to arrange for entry to NASA/Ames.

As the deadline for abstract submission approaches, we would also like to update you on several important changes made by the MER project at JPL. The first relates to a southward shift in the acceptable landing latitude for MER-B, the second to changes in the size and orientation of the landing ellipse for both MER-A and MER-B, and the third focuses on the process of identifying high-priority sites for imaging by the Mars Orbiter Camera (MOC) during the initial stages of the Mars Global Surveyor (MGS) extended mission. It is important that you review these changes carefully as they will affect whether proposed landing sites can be considered.

First, with respect to the acceptable landing latitude for MER-B, the separation of the landing of MER-B from MER-A has been reduced to 35 days. This change necessitates a shift in the latitude band for MER-B southward from 15°N–5°S to 10°N–10°S. Although this change results in substantially improved data links and power budgets early in the mission, some 31 sites previously identified for MER-B are now outside the latitude land and will no longer be considered (see Table 1). Visibility of the landers by the Deep Space Network (DSN) during entry, descent and landing also places restrictions on landing sites that fortunately do not appear to limit the location of possible sites, but may become a factor in the future.

Second, changes in arrival time for MER-B and further analysis of the entry geometry and subsequent descent and landing for both MER-A and MER-B have resulted in changes to the ellipse size and orientation from those shown earlier. Preliminary estimates of landing ellipse orientation and size for early in the launch window are shown below (see Table 2). For MER-A note the difference in orientation relative to what was used previously, as well as the smaller ellipse size at the southern latitudes. For MER-B the orientation is quite different and the ellipse size is substantially smaller. These changes will produce a slightly different set of potential landing sites from what is presently indicated at http://marsoweb.nas.nasa.gov/landingsites/ and http://webgis.wr.usgs.gov/. The greatest effect is the smaller ellipse size, which will likely result in more potential sites for each lander. These estimates of ellipse size and orientation are still preliminary and are subject to change.

Additionally, the Thermal Emission Spectrometer (TES) has returned new thermal inertia and albedo data that are at higher spatial resolution than previous Viking IRTM data. These data have been analyzed and described by Mellon et al. [2000]. Seven sites (see Table 3) previously identified as possible with respect to fine component thermal inertia in the IRTM appear to be borderline acceptable in the new TES data. These seven sites have bulk thermal inertia values of less than 4 cgs units, or 160 SI units, indicating the existence of a dusty surface. Given the established fine component thermal inertia minimum of 3–4 cgs units, bulk inertias of <4 cgs units will also be too dusty. These sites are not rejected herein, but will require special consideration with respect to their surfaces to be acceptable.

Third, as the start of the MGS extended mission approaches, there are plans to use a significant fraction of the high-resolution MOC images for landing site selection. Currently, about one-third of the MOC images are to be targeted on landing sites of interest to future landers, most immediately the MER missions. The MGS project and Mike Malin (MOC PI) have begun detailed planning on how the spacecraft will operate, the ability to obtain non-nadir images during planned spacecraft rolls, and the tradeoff of this type of image acquisition verses normal nadir operations. Efforts indicate that a preliminary list of landing sites is needed a couple of months prior to actual targeting and acquisition of MOC images beginning in the February 2001 time frame. Although this list would obviously change after the first landing site workshop and the resultant identification of high-priority landing sites, it is to the advantage of all involved to have a preliminary list for initial MOC acquisition as soon as possible.

Toward this goal, we would like your help in identifying scientifically high priority landing sites for the MER missions. In order to accomplish this, we are requesting that you submit a list of scientifically interesting sites (up to five per investigator) that meet the preliminary engineering requirements (e.g., as modified above and described at http://marsoweb.nas.nasa.gov/landingsites/ and http://webgis.wr.usgs.gov/) and that look reasonably safe in existing MOC images.

It is expected that most everyone proposing a landing site for the workshop will be preparing such a list as part of the preparation of an abstract for the workshop. Hence, we are requesting that you submit your list of sites at the same time. For each site submitted, identify (1) the site name if it is already in the list of potential sites; (2) the scientific merits/objectives of the site; (3) a list of existing MOC images of the site; (4) remote sensing data of the site (e.g., thermal inertia, rock abundance and albedo); and (5) why the site should be considered safe for landing. Upon receiving the list of sites, they will be tabulated and used for beginning the task of MOC targeting. The list of potential sites and MOC targeting will be updated following the workshop in January.

Send your list of up to five sites by December 8, 2000, via e-mail to John Grant, Matt Golombek, and Tim Parker (GrantJ@nasm1.si.edu, mgolombek@jpl.nasa.gov, and Timothy.J.Parker@jpl.nasa.gov). Be sure to include information related to all five items discussed above for each site. Note that landing site abstracts are also due December 8, 2000, and are to be submitted using the electronic submission form. We look forward to receiving your list of high-priority science landing sites and your abstracts for the landing site workshop as well as your participation in the landing site selection process.

References Cited:
Greeley, R., and J. E. Guest, Geologic map of the eastern equatorial region of Mars, U. S. Geological Survey Miscellaneous Investigation Map I-1802-B, 1987.

Mellon, M. T., B. M. Jakosky, H. H. Kieffer, and P. R. Christensen, High resolution thermal inertia mapping from the Mars Global Surveyor Thermal Emission Spectrometer, Icarus, in press, 2000.

Scott, D. H., and K. L. Tanaka, Geologic map of the western equatorial region of Mars, U. S. Geological Survey Miscellaneous Investigation Map I-1802-A, 1986.


Regards,
John Grant and Matt Golombek
Co-Chairs, Mars Landing Site Steering Committee

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