The presence of these canals made Astronomers think this planet could have supported life once, which planet are we talking about?

In the late 19th century, astronomers observed what they believed to be canals on Mars through telescopes, most notably by Giovanni Schiaparelli and Percival Lowell. These "canali" (Italian for channels or grooves) were misinterpreted as artificial waterways built by intelligent Martians. This led to widespread speculation about Martian civilization and the possibility that Mars had once supported life. Later missions proved these "canals" were optical illusions and geological features.