Was there ever water on Mars?

The answer

Overwhelming geological evidence from orbiters and rovers confirms that Mars once had abundant liquid water. Curiosity and Perseverance rovers have found layered sedimentary rocks, ancient riverbeds, lake deposits, and minerals that only form in water. Mars may have had a vast northern ocean covering a third of its surface about 3.5 to 4 billion years ago. The planet lost its water as its magnetic field weakened, allowing solar wind to strip away its atmosphere. Today, water exists as polar ice caps and possibly as subsurface brines. The Mars Sample Return mission aims to bring Martian rocks to Earth for detailed analysis.