# Presentation: 054648

## SHOEMAKER CRATER – GOING WHERE WE CAN “SEE”

**SHOEMAKER CRATER – GOING WHERE WE CAN “SEE”**

- Carlton Allen
- NASA JSC

## Recommended impact site for LCROSS:

_**SHOEMAKER CRATER**_
**This 51-km diameter crater centered at 88.1 S, 45 E**
** ****is in permanent shadow  **
**Half of its floor can be imaged by Earth-base radar**
**This degree of target knowledge will strongly constrain impact models and significantly increase the confidence of data interpretation.**

## Lunar Orbiter IV and Clementine images of Shoemaker show that the rim is partially illuminated by sunlight, but the crater floor remains dark.  

**Clementine mosaic**

## Radar interferometry digital elevation model (DEM) 150 m spatial resolution and 50 m height resolution 

**Radar interferometry digital elevation model (DEM) 150 m spatial resolution and 50 m height resolution**

**Radar DEM**

## Radar DEM, combined with ray tracing, highlights five craters in which a portion or all of each floor is in permanent shadow. 

**Radar DEM, combined with ray tracing, highlights five craters in which a portion or all of each floor is in permanent shadow.**

**Radar DEM**

## Intact rim with numerous 1 - 10 km superimposed craters; ejecta blanked is totally subdued

**More degraded than Shackleton, but less degraded than other craters in the region**

**Radar DEM**

## Crater floor diameter is approximately 20 km

**Floor is flat and partially smooth, with scattered impact craters**
**Crater is simple in plan, with no evidence of a central peak**

**Radar DEM**

## Thermal and epithermal neutron counts measured by Lunar Prospector suggest concentrations of near-surface ice.  

## Radar beams with wavelengths of 2.5, 12.6, and 70 cm have returned echoes that are typical of highland terrain, without the strong echoes attributable to ice.  

## In 1999 Lunar Prospector was deliberately crashed into Shoemaker crater.  

**Earth-based sensors detected no ejecta plume.  **

**LCROSS will impact the Moon with ~200 x more kinetic energy, and the impact will be observed by from lunar orbit as well as from Earth.**

## Many targets meet the LCROSS criteria:

**  ****nearside**
**  ****permanently shadowed**
**  ****poleward of 70 degrees latitude**
**  ****large enough to contain a 10 km landing ellipse**
**The actual material to be impacted in most of these candidates is unknown.**

## Shoemaker crater is unique among possible targets – half of the floor has been imaged by radar.  

**The physical properties of the floor material can be modeled.  **
**This target is known to be flat, providing simple geometry for understanding impact dynamics and the ejecta plume.**

## Importance of imaging the target area in a spacecraft impact experiment was demonstrated by the Deep Impact mission to Comet Temple 1.

**Close-up images of the impact point, revealing layered target material, strongly constrained the comet model.**

## Shoemaker is large enough to cover a substantial portion of a Lunar Prospector neutron detector pixel, and so contributes directly to that ice “detection”.  

**Half of the floor is within sight of Earth-based radar and was probed as part of the null ice “detection” by that technique**
**Shoemaker crater provides a unique opportunity to test the seemingly-contradictory neutron and radar results concerning near-surface ice.**

## LCROSS impact into Shoemaker will directly test these two results at the same location, and should significantly improve our understanding of lunar ice.