The Phoenix Mars Lander is scheduled to lift off for Mars next month:

NASA Spacecraft Set to Study Mars' Icy North Pole
By Ker Than
Staff Writer
posted: 9 July 2007 2:09 pm ET
http://www.space.com/missionlaunches...ix_update.html

It is to land in the north polar region of Mars but the exact lander location has not yet been chosen.

I propose as possible lander sites those areas that have been suggested to contain geologically young polar volcanoes:

TOPOGRAPHY OF SMALL VOLCANOES AT THE MARGIN OF THE MARS NORTH POLAR CAP.
S.E.H. Sakimoto1, J. B. Garvin2, M. Wong1, and H. Wright1,3; 1(USRA at NASAÕs GSFC, Code 921, Greenbelt, MD 20771 USA; ****@denali.gsfc.nasa.gov), 2(NASA's GSFC, Code 921, Greenbelt, MD 20771 USA; ****@denali.gsfc.nasa.gov), 3 (USGS, Menlo Park, CA, 94025).
http://www.lpi.usra.edu/meetings/polar2000/pdf/4092.pdf

Also, dunes in the north polar region have been the only sites so far that are geologically young proven to contain sulfates:

CRISM SPECTRAL SIGNATURES OF THE NORTH POLAR GYPSUM DUNES.
L.H. Roach1, J.F. Mustard1, S. Murchie2, Y. Langevin3, J.-P. Bibring3, J. Bishop4, N. Bridges6, A. Brown4, S. Byrne7, B.L. Ehlmann1, K. Herkenhoff7, P.C. McGuire5, R.E. Milliken6, S. Pelkey1, F. Poulet3, F.P. Seelos2, K. Seelos2, and the CRISM team.
1Dept. of Geological Sciences, Box 1846, Brown University, Providence, RI 02912 ****@brown.edu, 2JHU/APL, Laurel, MD 20723, 3Institute d’Astrophysique Spatial (IAS), Orsay, France, 4SETI Institute, Mountain View, CA 94043, 5Washington University in St. Louis, St. Louis, MO 63130, 6JPL/Caltech, Pasadena, CA 91109, 7USGS, Flagstaff, AZ 86001
Lunar and Planetary Science XXXVIII (2007)
http://www.lpi.usra.edu/meetings/lpsc2007/pdf/1970.pdf

FORMATION OF THE MARTIAN NORTH POLAR GYPSUM DEPOSIT DURING THE AMAZONIAN.
K. E. Fishbaugh1, F. Poulet2, Y. Langevin2, V. Chevrier3, and J-P. Bibring2. 1International Space Science Institute (ISSI), Hallerstrasse 6, Bern CH-3012 Switzerland, ****@issi.unibe.ch. 2Institut d'Astrophysique Spatiale (IAS), Bâtiment 121, 91405 Orsay Campus, France. 3CEREGE, Europóle de l’Arbois, BP80, 13545 Aix-en-Provence Cedex 04, France.
Fourth Mars Polar Science Conference (2006)
http://www.lpi.usra.edu/meetings/polar2006/pdf/8041.pdf

The origin of the sulfate deposits is not known. It has been proposed extensive volcanism from far away volcanoes such as in Tharsis deposited sulfurous dust to the region and obliquity changes allowed the liquid water required for the sulfate formation.
However, it may be the near polar volcanoes are the source of the sulfate dunes. This would be very interesting because these volcanoes date to within only a few million years and some may still be active. Such volcanoes would have provided a local source for the large amount of sulfur required and the liquid water due to the heating generated.
The largest sulfate deposit is around 80N latitude and 240E longitude. And this Icarus article shows there are volcanic landforms at several different longitudes at around 80N, some close to the 240E longitude of the densest sulfate deposit:

North Polar Region Craterforms on Mars: Geometric Characteristics
from the Mars Orbiter Laser Altimeter.
Icarus 144, 329–352 (2000).
http://ssed.gsfc.nasa.gov/tharsis/garvin_icarus.pdf

However, since there are several volcanic landforms at this latitude at different longitudes it can't be confirmed for certain any one of them is the source of the sulfate deposits.
The polar dunes with the densest sulfate deposits are seen around 80 N latitude which is too high in latitude for Phoenix which has to land at 72 N or lower. However, some of the north polar volcanoes do lie around 72 N latitude:

SMALL MARTIAN NORTH POLAR VOLCANOES: TOPOGRAPHIC IMPLICATIONS FOR ERUPTION STYLES.
S. E. H. Sakimoto1, J. B. Garvin2, B. A. Bradley3, M. Wong4, J. J. Frawley5
Lunar and Planetary Science XXXII (2001)
http://www.lpi.usra.edu/meetings/lpsc2001/pdf/1808.pdf

And, a map by OMEGA of north polar sulfates shows they do occur at around 70 N though in lower concentrations:

REMOTE SENSING OBSERVATIONS AND IMPLICATIONS OF MARTIAN NORTH POLAR SULFATE DEPOSITS.
B. H. N. Horgan1, J. F. Bell III1, E. Z. Noe Dobrea2, and P. C. Thomas1, 1Cornell University, Department of Astronomy (****@astro.cornell.edu), 2Malin Space Science Systems (now at Jet Propulsion Laboratory).
Seventh International Conference on Mars.
http://www.lpi.usra.edu/meetings/7th...7/pdf/3241.pdf

It would be interesting to find out if the lower concentration sulfates at the lower polar latitudes also correlate in position to the lower latitude polar volcanoes.

The landing regions for Phoenix under consideration are shown in the first image attached, taken from Fig. 1 of the report:

OVERVIEW OF MARS EXPLORATION PROGRAM 2007 PHOENIX MISSION LANDING SITE SELECTION.
Seventh International Conference on Mars.
http://www.lpi.usra.edu/meetings/7th...7/pdf/3204.pdf

Region D currently is the leading location for the landing.


Caption to Fig. 1:

"Figure 1. Polar perspective view of MOLA topography
with Regions A, B, C, and D shown. Each Region
covers the latitude range from 65° to 72° N. Region A
covers 250° to 270°, B 120° to 140°, C 65° to 85°, and
D 230° to 250° E."

A map by OMEGA of the north polar sulfate deposits is the second image attached below, taken from Fig. 3 of the report:

REMOTE SENSING OBSERVATIONS AND IMPLICATIONS OF MARTIAN NORTH POLAR SULFATE DEPOSITS.
B. H. N. Horgan1, J. F. Bell III1, E. Z. Noe Dobrea2, and P. C. Thomas1, 1Cornell University, Department of Astronomy (****@astro.cornell.edu), 2Malin Space Science Systems (now at Jet Propulsion Laboratory).
Seventh International Conference on Mars.
http://www.lpi.usra.edu/meetings/7th...7/pdf/3241.pdf

I drew in an arrow in red indicating the location of the lower concentration sulfate deposit at about 70N latitude, 230E longitude, within the possible Phoenix landing area Region D.

Caption to Fig. 3:

"Figure 3: Distribution of Ca-bearing sulfate, based on
1.92 μm band depth, ranging from 0 to 25% band depth below
the continuum. Grayscale regions are residual water ice."



Bob Clark

Attached Images

	750931-Phoenixlandingsites.jpg (37.7 KB, 2 views)
	750933-Sulfatemap-comp.jpg (60.9 KB, 1 views)

On Uplink.space.com was discussed a possible landing site for Phoenix that is within the leading candidate region:

HiRISE | Possible Phoenix Lander Landing Site (PSP_002104_2485)
http://hirise.lpl.arizona.edu/PSP_002104_2485

It's located at 68.3°N lat., 233.9° E long. This means it's close to the sulfate deposit I mentioned at about 70°N lat., 230°E long.
Notice the image contains one and possibly two volcanic landforms. They might be the origin of the nearby sulfate deposits.


Bob Clark

This report shows a meltwater channel in Fig. 1 near the largest polar sulfate deposit:

FORMATION OF THE MARTIAN NORTH POLAR GYPSUM DEPOSIT DURING THE AMAZONIAN.
K. E. Fishbaugh1, F. Poulet2, Y. Langevin2, V. Chevrier3, and J-P. Bibring2. 1International Space Science Institute (ISSI), Hallerstrasse 6, Bern CH-3012 Switzerland, ****@issi.unibe.ch. 2Institut d'Astrophysique Spatiale (IAS), Bâtiment 121, 91405 Orsay Campus, France. 3CEREGE, Europóle de l’Arbois, BP80, 13545 Aix-en-Provence Cedex 04, France.
Fourth Mars Polar Science Conference (2006).
http://www.lpi.usra.edu/meetings/polar2006/pdf/8041.pdf

Perhaps the meltwater channel was formed by a near polar volcano. If so, it should be located near the origin of the channel. Unfortunately, the image doesn't show the start of the channel.
Anyone able to locate MOC or THEMIS images of this channel that shows the location of the origin of the channel? Then it could be determined if volcanic landforms lie nearby.


Bob Clark

Attached Images

polarmeltchannel.jpg (25.4 KB, 1 views)

Here's a MOC image of a north polar cone:

Polar Cone
MGS MOC Release No. MOC2-1519, 10 July 2006.
http://www.msss.com/mars_images/moc/2006/07/10/

It's located at 79.5°N, 57.0°W (303°E).
If you look at the image I copied above containing the meltwater channel, the channel seems to be headed towards the location of this cone. But since you can't see the origin of the meltwater channel, you can't tell if the polar cone is close to the channels origin.
However, the caption to the image of the polar cone claims it is not a volcano, but does not provide the argument for why it is believed not to be.
I attached a copy of the polar cone image below. I rotated it 90° clockwise to make it clearer it's a raised feature.


Bob Clark

Attached Images

PIA08583-comp.JPG (9.7 KB, 5 views)