Context : There is evidence to suggest that clathrate hydrates have a significant effect on the surface geology of icy bodies in the Solar System .
However the aqueous environments believed to be present on these bodies are likely to be saline rather than pure water .
Laboratory work to underpin the properties of clathrate hydrates in such environments is generally lacking .

Aims : We aim to fill this gap by carrying out a laboratory investigation of the physical properties of CO _ { 2 } clathrate hydrates produced in weak aqueous solutions of MgSO _ { 4 } .

Methods : We use in situ synchrotron X-ray powder diffraction to investigate clathrate hydrates formed at high CO _ { 2 } pressure in ice that has formed from aqueous solutions of MgSO _ { 4 } with varying concentrations .
We measure the thermal expansion , density and dissociation properties of the clathrates under temperature conditions similar to those on icy Solar System bodies .

Results : We find that the sulphate solution inhibits the formation of clathrates by lowering their dissociation temperatures .
Hysteresis is found in the thermal expansion coefficients as the clathrates are cooled and heated ; we attribute this to the presence of the salt in solution .
We find the density derived from X-ray powder diffraction measurements is temperature and pressure dependent .
When comparing the density of the CO _ { 2 } clathrates to that of the solution in which they were formed , we conclude that they should sink in the oceans in which they form .
We also find that the polymorph of ice present at low temperatures is Ih rather than the expected Ic , which we tentatively attribute to the presence of the MgSO _ { 4 } .

Conclusions : We ( 1 ) conclude that the density of the clathrates has implications for their behaviour in satellite oceans as their sinking and floating capabilities are temperature and pressure dependent , ( 2 ) conclude that the presence of MgSO _ { 4 } inhibits the formation of clathrates and in some cases may even affect their structure and ( 3 ) report the dominance of Ih throughout the experimental procedure despite Ic being the stable phase at low temperature .