Mapping the Thermal Inertia of Iapetus
Abstract
Nighttime temperatures on a slow rotating airless body, such as Iapetus, are a critical indicator of the surface thermal inertia since during this time the only active heat source is the stored thermal energy within the surface material. During a PRIME data set for ISS in 2007, the Cassini CIRS instrument was given the opportunity to record data at such a time. Surface temperatures deduced from thermal emissions are thus far the lowest recorded for Iapetus. To account for the observed low temperatures, a much lower thermal inertia than previously estimated is required. Surface thermal inertia is expected to vary if dark material overburden thickness varies on the surface of Iapetus. This arises from the finding that for a heterogeneous mixture where the surface material has a lower thermal inertia than the underlying layer, the surface proximity of the high thermal inertia material strongly affects the observed surface thermal inertia (Mellon et al., 2004, Icarus, 169, 324-340). Indeed, it has been suggested that albedo is a function of dark material thickness (Spencer and Denk, 2010, Science, 327, 432-435) thus it can be shown that surface thermal inertia is a function of albedo. Via the use of a heat transfer model and the recently published Iapetus bolometric Bond albedo map (Blackburn et al., 2010, Icarus, Submitted), surface thermal inertia can now be extrapolated for several albedo points on Iapetus. This allows for an estimate of the albedo/thermal inertia relationship and thus the development of a global thermal inertia map. We will discuss the implications for surface material composition focusing on the material properties of the dark terrain.
- Publication:
-
AAS/Division for Planetary Sciences Meeting Abstracts #42
- Pub Date:
- October 2010
- Bibcode:
- 2010DPS....42.0906R