Thermal inertia SI unit proposal
Excerpted from Section 1.2 of Putzig (2006)
Historically, thermal inertia has been given in units of cal cm-2 K-1 s-½, 103 cal cm-2 K-1 s-½ *, and more recently in SI units of J m-2 K-1 s-½. Regardless of the base system, these units are typographically cumbersome and can be visually distracting. They are nearly always either abbreviated (e.g., as 'IU' by Presley and Christensen 1997b and 'SI Units' by Golombek et al. 2003), or, more commonly, given once and thereafter assumed and left off altogether (e.g., by Kieffer et al. 1977, Jakosky 1979, Palluconi and Kieffer 1981, Christensen 1986b, Hayashi et al. 1995, Mellon et al. 2000, and Putzig et al. 2005). Neither solution is ideal. In one case, we have a varying set of ad hoc units; in the other, bare numbers whose units are only ascertained upon a close examination of the early portions of the text. This situation suggests the introduction of a new standard derived SI unit. To that end, I hereby propose a new SI unit designation of 'tiu' such that:
tiu = J m-2 K-1 s-½.
While 'tiu' may be viewed as an acronym for thermal inertia units, it is also the name for Mars in Old English (e.g., Tiu Vallis) and incidentally serves as the root word for Tuesday (Pickett et al. 2000). Naming this unit after Mars is appropriate because conditions on the surface of Mars are uniquely tuned to take greatest advantage of thermal inertia as a measure of surface physical properties (Wechsler et al. 1972, Jakosky 1986, Presley and Christensen 1997a). Furthermore, 'tiu' is terse enough to encourage its inclusion throughout a journal paper, yet unique enough to avoid confusion with other units or English words.
* The units 103 cal cm-2 K-1 s-½ have been informally referred to as "kieffers", but some have also used this term in reference to the SI units.
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