A 200-mile river valley, dubbed a mini-Nile, has been discovered on Saturn's moon, Titan.
Smaller rivers and water features have previously been found on Titan, but the size of this river, stretching across the north of the moon, is the first find of its scale.
Christian Huygens, the astronomer who discovered Titan in 1655, predicted such a phenomenon back then.
"Since 'tis certain that Earth and Jupiter have their Water and Clouds, there is no reason why the other Planets should be without them," he said.
Titan's "water" is not like Earth's but is liquid methane or natural gas.
H2O would be frozen solid on Titan where the surface temperature is around -143 degrees Celsius (-290 degrees Fahrenheit).
Scientists say the source of all the wetness might be rain, since the moon's atmosphere is "humid" and periodic showers have been recorded.
The latest discovery gives Titan the potential for an earth-like landscape.
"The ingredients you need for a rainbow are sunlight and raindrops. Titan has both," said atmospheric optics expert Les Cowley.
There may also be waves on Titan, which, space experts estimate, could be up to seven times taller than those on Earth and three times slower.
While there is no proof of life on Titan, scientists say all these findings make it a possibility.