Huge Water Reserves Found All Over Mars

Gullies fringe the edge of southern Mars's Hale crater. On Earth, these structures usually form through the action of liquid water.

In 2004, the NASA Mars rover Opportunity found sphere-like grains nicknamed "blueberries." These grains of hematite probably formed in wet sediments.

Alluvial fans are gently sloping wedges of sediments laid down by flowing water. Some of the best-preserved alluvial fans on Mars are in Saheki Crater, seen here.

In 2015, scientists found dark streaks flowing down some Martian hillsides. Initially, salty liquid water was considered the culprit, but recent studies suggest that the streaks are in fact dry cascades of dust.

In October 2017, scientists unveiled evidence that 3.7 billion years ago, Mars's Eridania basin was a vast ocean with hydrothermal vents—potentially offering conditions friendly to ancient life.

Gullies snake down the northwest rim of Hale crater. It's unclear how the gullies formed, but some resemble features on Earth that are carved by flowing water.

In 2012, NASA's Curiosity rover found the remains of a stream that once ran vigorously across Mars's surface. These rocks, which contain ancient streambed gravels, were the first of their kind found on Mars.

The pinkish, scaly texture is Martian bedrock that water altered long ago, forming clay-bearing rocks. It's still unclear how exactly the rock and water interacted.