Considering its mythological namesake, it's entirely appropriate that there's water on Neptune. But we still don't entirely understand how the gas giant warps water into something unrecognizable. Now plans are afoot to replicate these conditions in a lab.
A team of researchers from the European Union, Russia, and China are drawing up plans to bombard water molecules with heavy ion beams, recreating the tremendous pressure found on Neptune. The experiment is still a ways off – it requires the use of Germany's Facility for Antiprotons and Ion Research, or FAIR, which won't be ready until 2015. Once completed, FAIR can create pressures millions of times greater than anything found on Earth, which is just what's needed to simulate the conditions of Neptune.
Until then, we are left to speculate on how water behaves on Neptune under such unique circumstances. The extreme pressure is believed to forced the water into what's known as a superionic state. This is a very exotic form of water in which an oxygen lattice and liquid hydrogen come together to form stable water molecules that are either in ice or liquid form.
Figuring out how the superionic state works could be hugely useful in understanding the magnetic fields of both Uranus and Neptune, which are very unlike Earth's. The heavy ion beams that FAIR will use are preferable to other methods for recreating extreme pressure, which includes everything from lasers to explosives, because they offer a much more uniform, targeted pressure on the water.