Was it a hidden phase change question? Placing a liquid into a vacuum will convert it into a gas, which will have a definite density decrease. If the liquid is ideal, and therefore non-compressible, it should not be affected by changes in external pressure. If it is not ideal, then the density will decrease by a slight amount if placed into a vacuum.
another question, what happens to a shuttle that is in a circular orbit when it increases its tangential acceleration? does the radius increase or decrease? or does it move to an eliptical orbit? or does it spiral into space?