How come we can explore space with relative 'ease' (most things we send up there that I hear about seem to work without failing) yet most of our oceans are unexplored?
The deep ocean is a very difficult environment to explore. Some of the pressures that would be present at sea level are zero in space, which makes going deeper into the ocean a less stressful experience. [1] The depth of the water also plays a role, as some areas of the ocean are deeper than 3200 meters (elliptical orbit) and cover in ice, making it more difficult to explore. [2]Tools like sonar can be used to generate maps of the deep ocean, but they are limited in what they can do and are expensive to create. [3] Additionally, half of the ocean is deeper than 3200 meters, and a lot of it is covered in ice, which makes creating a global basemap difficult. [2]
Compared to NASA's unprecedented 20 meter resolution Martian maps, almost everything produced by bathymetry is seemingly light years behind [3]. Unlike the moon and planets, the seafloor can't be mapped using radar, since ocean water tends to obstruct a satellite's radio waves [3]. In order to capture high-resolution images of the bottom of the ocean, experts will need to deploy a series of sophisticated sonar techniques, which can map a small sliver of the seafloor to a resolution of about 100 meters [3]. Obviously, with 95% of the ocean still unexplored, space exploration is still quite a challenge. But compared to the ocean, space exploration is quite advanced! [1, 4]