Final answer:
Mars has shown evidence of past liquid water and organic compounds, whereas moons like Europa and Enceladus may harbor subsurface oceans, and Titan offers a unique environment with hydrocarbon lakes. Mars rovers have been instrumental in these discoveries. These findings have fueled extraterrestrial life research, including the SETI program.
Step-by-step explanation:
One of the most significant discoveries that supports the theory of liquid water on planets other than Earth is the evidence from Martian samples that revealed both water and organic compounds, suggesting that Mars may once have hosted oceans and possibly life. The presence of mineralogy in rocks and unique layering of rock formations analyzed by the Mars rovers, including Opportunity and Curiosity, indicates a history of liquid water on Mars. Moreover, Mars's polar ice caps and gullies suggest current water activity, potentially from subsurface water or near-surface aquifers.
Apart from Mars, Jupiter's moon Europa is believed to have a subsurface ocean beneath its ice shell that could harbor biology. Saturn's moon Enceladus is also of interest due to geysers that eject water into space, indicating the presence of liquid water below. Titan, although extremely cold, holds interest with its thick atmosphere and hydrocarbon lakes, suggestive of unique life forms.
These findings have sparked widespread research and discussion, including programs such as the Search for Extraterrestrial Intelligence (SETI), with the aim of answering the question of whether we are alone in the universe.