Experiments in the NH3-H2O system in the [0,1 GPa] pressure range - implications for the deep liquid layer of large icy satellites

Research areas:
Year:
2002
Authors:
Journal:
GEOPHYSICAL RESEARCH LETTERS
Volume:
29
Number:
24
Month:
DEC 26
ISSN:
0094-8276
BibTex:
Abstract:
[1] We have experimentally studied the peritectic's melting
temperature of a 25 wt\% ammonia water solution in the [0, 1 GPa]
pressure range by using a high pressure low temperature membrane
sapphire anvil cell with nitrogen cooled cryostat. Our experimental
results are in agreement with those presented by Hogenboom et al.
{[}1997] in the {[}0, 0.4 GPa] pressure domain where the peritectic's
melting temperature follows a plateau at 180 K. The present experimental
work fills the lack of data between 0.4 and 0.7 GPa. It also suggests
that the peritectic's melting temperature is much higher than that
between 0 and 0.4 GPa and does not vary very much with pressure at least
up to 1 GPa. This implies the existence of two new high pressure phases
in the ammonia-water system. The behaviour of the peritectic's melting
curve above 0.5 GPa might play an important role in the evolution of a
deep liquid layer in the interiors of the largest icy satellites
including Titan, Ganymede and Callisto. We show that the cooling of the
deep liquid layer may have involved the crystallization of an ammonia
bearing phase at higher temperature than previously expected. If the
initial fraction of ammonia relative to ices is greater than 11 weight
per cent, taking the partial ammonia depletion into account may lead to
a final liquid layer thinner than previously inferred.