Elliot Sefton-Nash, Matt Siegler, David Paige

LRO Diviner Team Meeting – UCLA – Weds. Feb. 13th 2013 – 09:00

Thermal Extremes in South Pole PSRs (LPSC Abs. #2617)

Body of results to date yields a relatively inconclusive answer to the question of volatile abundance at the surface or in the near-surface in PSRs.

LCROSS observed a suite of volatiles, dominated by water, at Cabeus (Colaprete et al. 2010, Science), but there are plenty of other cold traps (Paige et al, 2010, Science).

Observations could indicate:Very thin veneer of water ice frost (Gladstone et al. 2012, JGR)Freshly exposed/weathered regolith e.g. Riner et al., LPSC 2013 Abs. 2677, Zuber et al. (2012), Nature and Haruyama et al. (2008) Science.

What is the range of thermal behaviour in PSRs and does that help constrain volatile presence?

Thermal extrema within PSRs may be governed by regolith/volatile properties, heat flow from the interior and non-solar radiation sources, e.g. other surfaces in line of sight (less in double/triple shadowed).

In lieu of TBOL (will have by LPSC!), choose channels with appropriate spectral response for PSR temperatures:

Channel 8 (50 – 100 μm) 43 to 69 KChannel 9 (100– 400 μm) < 43K

Haworth: Some areas show TB8 maximum never exceeds ~50K. This is also the region with the lowest range of brightness temperatures.

Faustini: Small doubly-shadowed crater near northeast rim. Year-round thermal stability at < 50K.

Shackleton: Relatively high maximum and minimum brightness temperatures, a wide thermal range compared to other major PSRs, with the exception of the poleward crater wall, which exhibits a comparatively narrow thermal range.

Shackleton:

Plausible causes of high 1064nm albedo (LOLA) and low UV albedo (LAMP) include regolith brightening by mass wasting, the effects of space weathering at low temperatures or minor amounts of surface ice (Gladstone et al., 2012 - JGR, Zuber et al. 2012 - Science).

However, recent comparison of Shackleton’s LOLA albedo with a broad crater population sampled from PSRs and equatorial regions indicate that Shackleton is not anomalously bright: surface volatiles not required to explain its appearance (Riner et al., LPSC 2013, Abs. 2677).

Ongoing work:

Run all thermal channels to make TBOL maps (stack grids separated by orbit number).

Explore 'thermal ring' effect caused by buried areas of higher thermal conductivity (M. Siegler)

Constrain errors. Especially for ultra low channel 9 temperatures. Is error within limits required for heat flow measurement?