# Presentation: 130129

## Gully Analysis by the 2009 Mars Science Laboratory

**W. E. Dietrich, J. Schieber, B. Hallet, **
**K. S. Edgett and M. C. Malin**

## Gullies are located at Middle and Polar Latitudes and Might be Key Sites for Recent Water and Habitability Science

## There’s a variety of morphologic expressions...

**~3 km across, E16-00043, 41.8°S, 158.0°W**

## ...more examples...

## ...and more examples..

**~ 3 km wide, S10-00964, 38.0****°S****, 167.2****°W**

## 

Banked channels
Multiple flow events
Not cratered

- Banked channels
- Multiple flow events
- Not cratered

**...****and another...**

## They Seem to Be Young

- Superimposed craters are uncommon.
- Some have dark floors; do not retain dust.
- Some cut or superpose eolian bedforms.
- Not all are young; some do have superposed craters or eolian bedforms; some have features cut by cracks or faults.

## How Do They Form?

| Hypothesis | References |
| --- | --- |
| H2O groundwater  | Malin and Edgett (2000)
Mellon and Phillips (2001)
Gilmore and Phillips (2002)
Heldmann and Mellon (2004) |
| H2O ground ice | Costard et al. (2001) |
| H2O ice pack, snowmelt, atmospheric precipitation | Lee et al. (2001)
Christensen (2003)
Balme et al. (2006) |
| CO2 release | Musselwhite et al. (2001)
Hoffman (2002) |
| No volatile is involved; dry granular flow | Treiman (2003)
Shinbrot et al. (2004) |

## Malin/Edgett Still Favor Groundwater Hypothesis

- Bolstered by recent excellent evidence that fluids emerged from beneath the ground, rather than by melting of snow.
- Key examples include those at which gullies emerge at a fault, suggesting groundwater percolation along fault (image on far right).

## Can MSL Go to a Gully Site? D’oh!

- We recognize that Planetary Protection likely precludes landing at a gully site, but we feel it is important to have discussed this topic at the 1st Landing Site Workshop.
- It is critical to understand that, while MSL theoretically opens up a larger portion of Mars for landing than previous US surface missions, the design still precludes visiting certain key or critical targets.

## The Search for Places That a 20 km Diameter Landing Ellipse Will Fit

- We examined every gully location known from MOC images, acquired through 30 May 2006, in both hemispheres to 60° latitude.
- MSL obviously can’t land on gullied slopes.
- MSL likely can’t drive down into craters with gullied walls.
- So we sought craters with gullies that are large enough to put a 20 km diameter ellipse on the crater floor, snuggled up as close as possible to gully apron material.
- Most craters with gullies are too small for a 20 km ellipse.
- Most craters large enough for 20 km ellipse do not have gullies.
- We found only 3 viable locations, with two craters at one of the three locations

## Candidate 1 & 2: South Terra Cimmeria

- 35.8°S, 204.4°W

- 35.2°S, 203.9°W

- elevations are ~ +0.4 km

- White boxes show existing MGS MOC coverage to 30 May 2006.

## Gullies in Candidate 1 Crater

## Floor of Candidate 1 Crater

## Candidate 3: Hale Crater (floor too rugged)

- White boxes show existing MGS MOC coverage to May 2006.

## Many, Many Terrific Gullies in Hale (example)

## And in Hale’s Central Peak Area (example)

## But Hale’s Floor is Pretty Rough

## Candidate 4: Wirtz Crater (probably the best)

- White boxes show existing MGS MOC coverage to 15 May 2006.

## Example Gullies on NW Wirtz Wall

## Example Gullies on SE Wirtz Wall

## Example of Wirtz Crater Floor

## Summary

| candidate | name | approx. lat/lon | elevation | comments |
| --- | --- | --- | --- | --- |
| 1 | none | 36°S, 204°W | +0.4 km | ellipse just fits in crater; pretty good candidate |
| 2 | none | 35°S, 204°W | +0.4 km | ellipse barely fits in crater; not much MOC or THEMIS coverage |
| 3 | Hale | 36°S, 37°W | –2.4 km | many great gullies; floor is likely way too rugged |
| 4 | Wirtz | 49°S, 26°W | –0.6 km | probably the best candidate; several places that an ellipse will fit; floor (thus far) doesn’t look too dangerous. |

## Recommendation

- Consider sending MSL to a gully site.
- Unfortunately, there are very few gully sites accessible with a 20 km landing ellipse.
- Recognizing that going to gullies may not be possible, for Planetary Protection reasons, means there is something wrong with the system— how can NASA have not designed a mission (and its feed-forwardness) that could go to the only known class of sites on Mars where liquid water may have been present in relatively recent times?

*Mmmmm, gullies!*