EPSC
EPSC Abstracts
Vol. 8, EPSC2013-248, 2013
European Planetary Science Congress 2013
c Author(s) 2013
European Planetary Science Congress
Low temperature heat capacities of solar system materials
G. J. Consolmagno (1), M. W. Schaefer (2), B. E. Schaefer (2), D. T. Britt (3), R. J. Macke (1,4), M. C. Nolan (5) and E. S.
Howell (5)
(1) Vatican Observatory, Vatican City State, ([email protected] / Fax: +39-06-69884671) (2) Louisiana State University, USA,
(3) University of Central Florida, USA, (4) Boston College, Massachusetts, USA, (5) Arecibo Observatory, Puerto Rico,
USA
Abstract
We have devised a novel procedure for measuring the
heat capacity of meteorites at low temperatures. We
insert the sample in liquid nitrogen, determine the
mass of nitrogen boiled off due to the heat within the
sample, and from that calculate the total heat content
removed from the sample as it cools from 300 K to
77 K. The method is rapid, inexpensive, and nondestructive.
1. Introduction
Heat capacity is an essential parameter in many
aspects of asteroid models, from determining interior
thermal evolution to calculating the Yarkovsky and
YORP effects. Furthermore it can provide a nondestructive way of indicating the bulk composition of
a whole meteorite. To date, however, only a handful
of meteorite heat capacities have been published [1,
2, 3], virtually all at temperatures at or above 300 K.
Quantum Design’s Physical Properties Measurement
System is suitable for making low-temperature
measurements, but unfortunately it only measures
samples < 1g, and it is expensive both in terms of
sample consumption and time. One such
measurement has been published, of the shergottite
Los Angeles [4].
heat from the sample is determined. By measuring
how many grams of nitrogen are needed to cool the
sample from room temperature (about 300K; the
actual ambient temperature is recorded for each run)
down to liquid nitrogen temperature (77K), one can
derive the total heat content of the sample. To correct
for any systematic errors, we calibrate against
samples of electronics-grade quartz rather than
assuming the latent heat of liquid nitrogen. Dividing
the total heat content by the sample mass and the
change in temperature, one arrives at the average heat
capacity of the sample over this range of temperature.
Assuming a typical Debye temperature dependence
for heat capacity over this range, one can infer that
this average value is a good representation of the heat
capacity of materials at temperatures typical of the
asteroid belt, around 200K.
3. First Results
Our first results are shown in Figure 1. The lowest
values of heat capacity are for the metal-rich
meteorites Pirapora (iron type IIAB), Augustinovka
(iron type IIIAB), and Estherville (mesosiderite) at
around 350 J/g•K. This is consistent with the known
low heat capacity of metal. The mesosiderite has a
higher value than the pure irons, as expected for a
sample that is a mixture of basalt and metal.
Both theory and the Los Angeles measurement
indicate that heat capacity is a strong function of
temperature, especially at the lower temperatures
found in the asteroid belt. Typically one expects that,
in the absence of phase changes, the dependence at
low temperature will follow a characteristic curve
similar to that derived by Debye [5].
The H and L ordinary chondrite heat capacities, at
around 490 J/g•K, are indistinguishable at our present
precision. Most CO and CV carbonaceous chondrites
and our diogenite samples are just over 500 J/g•K,
slightly higher than the ordinary chondrites, but the
sparse data do not allow us to say that this difference
is statistically significant.
2. Technique
Metal content alone is not the only factor affecting a
meteorite’s heat capacity. The CR meteorite Renazzo
has a metal content of 7.4 vol.%, comparable to
ordinary chondrites, but it has the highest heat
capacity of our measured samples, at around 540 J/
g•K. This difference is presumably the result of its
A Dewar containing liquid nitrogen is placed on a
balance and its mass is measured over time as the
nitrogen evaporates. The sample is dropped into the
Dewar and the amount of nitrogen boiled off due the
significant water content (5.67 wt%) [6]. With this in
mind, one can expect that the heat capacity of metalfree, OH-rich meteorites such as those of the CM and
CI classes should be even higher.
Several chondrite finds have a higher heat capacity
value than similar falls, consistent with significant
amounts of metal have been oxidized in these
samples. However, not all ordinary chondrite finds
show this trend; thus heat capacity might be an
indicator of the degree of weathering that an ordinary
chondrite has experienced.
Among the carbonaceous chondrites measured, we
find that the CV fall Allende has a heat capacity
value similar to the ordinary chondrites; the COs
(Warrenton and Ornans) are slightly higher, but it is
not clear in the data at hand if this is significant. The
one find CV in our sample, NWA 2086, again shows
a higher heat capacity than the fall CV, Allende; this
may be significant, or it may simply be a reflection of
compositional differences between these two
meteorites.
meteorite composition. In particular, we confirm that
the average heat capacity of meteorites at
temperatures appropriate to the asteroid belt and
beyond is about half that of materials measured at
room temperature. We show that metal rich
meteorites are significantly lower in heat capacity
than stony meteorites. Our data suggest that it is very
likely that OH rich meteorites (and asteroids) will
have a higher heat capacity than anhydrous samples.
It is important to emphasize that these data are
preliminary, shown only to illustrate the nature of the
questions that might be addressed in future work.
Acknowledgements
The idea for this technique was inspired by a
conversation with Pierre Rochette and Jerome
Gattacecca. The contributions of MCN and ESH
were supported under NASA grant NNX12AF24G
through the Near-Earth Object Observations program
and funding from the OSIRIS-REx mission.
References
[1] Matsui, T., and Osako, M.: Thermal property
measurement of Yamato meteorites, Mem. Nat. Inst. Polar
Research, Special Issue 15, pp. 243–252, 1979.
[2] Beech, M., Coulson, I. M., Nie, W., and McCausland,
P.: The thermal and physical characteristics of the GaoGuenie (H5) meteorite, Planet. Space Sci. Vol. 57, pp. 764–
770, 2009.
[3] Szurgot, M.: On the specific heat capacity and thermal
capacity of meteorites, Proc. Lunar Planet. Sci Conf. 42,
abstract 1150, 2011.
Figure 1: Solid bars are the middle quartiles of the
data, extended lines the upper and lower quartiles;
open circles are two sigma away from of the mean.
4. Summary and Conclusions
We have developed a fast, inexpensive, and nondestructive system for measuring meteorite heat
capacities. The test data we have collected on
meteorites are consistent with both literature data
taken at higher temperatures and heat capacities
calculated for meteoritic material based on their
major mineralogy.
In our data to date we show important and
statistically significant trends in heat capacity with
[4] Opeil, C. P., Consolmagno, G. J., Safarik, D. J., and
Britt, D. T.: Stony meteorite thermal properties and their
relationship to meteorite chemical and physical states,
Meteorit. Planet. Sci., Vol. 47, pp. 319-329, 2012.
[5] Debye, P.: Zur Theorie der spezifischen Wärmen,
Annalen der Physik Vol. 344, pp. 789-839, 1912.
[6] Weisberg, M. K., Prinz, M., Clayton, R. N., and
Mayeda, T. K.: The CR (Renazzo-type) carbonaceous
chondrite group and its implications, Geochim.
Cosmochim. Acta, Vol. 57, pp. 1567-1586, 1993.