They go underground and see what there if it is deep they can use a submarine
From the oceans
It may have oceans of liquid water under its layers of water ice. Scientists want to know if these oceans (assuming they are there) contain any forms of life.
I think it is water collected in lakes, ponds, oceans, or other bodies of water.
Discard it all.
They go underground and see what there if it is deep they can use a submarine
Scientists believe that Earth's oceans formed about 4 billion years ago through a process called "outgassing," where water vapor and other gases were released from the Earth's interior through volcanic activity. As the Earth cooled, the water vapor condensed and fell as rain, filling the low-lying areas to create the oceans.
Because its rocks clearly show that it once had oceans made of liquid water.
Scientists call theories that explain all the evidence and are widely accepted by the scientific community "well-established theories" or "well-supported theories." These theories are based on a large body of evidence and have withstood rigorous testing and scrutiny.
Each scientists have there own opinion. Some accept theories and some have to have facts.
Astronomers believe that Mars has water, primarily in the form of ice, and there is evidence of seasonal liquid water flows on its surface. Additionally, scientists have detected water vapor in the atmospheres of several exoplanets and the icy moons of Jupiter and Saturn, such as Europa and Enceladus, which also harbor subsurface oceans.
Because they weren't there, so they have to work from ancient evidence, which isn't always clear.
Scientists think there may once have been large bodies of water on Venus, like oceans on Earth, but they all evaporated or something into space.