Before anyone points the finger saying this is a tasteless joke, there are some actual good reasons to pick that specific planet for exploration among the giants in our solar system:
- Smallest mass among the giants means an easier time navigating its gravity well;
- Only giant planet with a surface gravity smaller than Earth's;
- Mildest weather among the giants means less hassle navigating its atmosphere;
- Large tilt means longer days; a sol in there lasts for years, compared to less than an Earth sol for other giants.
Now that we have stablished the seriousness of the question, I really want to probe Uranus to get a feeling of what it's like. I know no gas or ice giant has a solid surface, but according to the wiki
The ice mantle is not in fact composed of ice in the conventional sense, but of a hot and dense fluid consisting of water, ammonia and other volatiles. This fluid, which has a high electrical conductivity, is sometimes called a water–ammonia ocean.
Very-high-pressure experiments at the Lawrence Livermore National Laboratory suggest that the base of the mantle may comprise an ocean of liquid diamond, with floating solid 'diamond-bergs'.
That got me thinking: maybe we could build a submarine or floating probe to explore Uranus. Unlike the probes that were sent to their doom into Saturn and Jupiter this one could last as long as it can stay afloat.
However, the same wiki also says:
The gaseous atmosphere gradually transitions into the internal liquid layers.
This is in line with a passage from the wiki on Jupiter:
In this state, there are no distinct liquid and gas phases—hydrogen is said to be in a supercritical fluid state. It is convenient to treat hydrogen as gas in the upper layer extending downward from the cloud layer to a depth of about 1,000 km, and as liquid in deeper layers. Physically, there is no clear boundary.
This is surrounded by a thicker liquid metallic hydrogen layer, followed by a liquid layer of helium-saturated molecular hydrogen that gradually transitions to a gas with increasing altitude.
I cannot get my head around this. On Earth, if you fill a container with gas and liquids, the gas stays on top and the liquid below, with a clear boundary. Even if the liquid is boiling or if the gas is condensing, we see distinct phases.
So, supposing we go for Uranus and send a splasher probe. Handwaving the problems related to getting it to resist the immense pressures and the low temperatures, would the probe be able to stay afloat - or at least keep a depth within a range - at some altitude?