Rivers on Earth are abundant, in spite of climate change that is evaporating many water sources. In 2018, scientists estimated that rivers and streams, excluding land with glaciers, covered nearly 300,000 square miles across the world.
But rivers aren't as prevalent in the rest of the solar system. As it stands, astronomers believe that there are only two other worlds in our solar system where rivers have flowed: Mars and Saturn's largest moon, Titan. Rivers on Mars haven't flowed for billions of years, but the red planet has been rocked by many cataclysmic events that stripped away its liquid water. All scientists can see today are the degraded remnants of rivers.
