Flowing liquid water essential to life is almost certainly present on Mars, scientists believe.
Experts think water is responsible for mysterious features on Mars that change with the seasons.
A new high resolution technique has revealed gully-like features at four locations, known as recurring slope lineae (RSL), contain salt minerals that precipitate from briny water.
The salts, which are not found in the surrounding terrain, are thought to have been left by water flowing down the sides of hills or crater rims.
Writing in the journal Nature Geoscience, the scientists concluded: "Our findings strongly support the hypothesis that recurring slope lineae form as a result of contemporary water activity on Mars".
"Water is essential to life as we know it. The presence of liquid water on Mars today has astrobiological, geologic and hydrologic implications and may affect future human exploration".
If the discovery is confirmed it has far-reaching implications for the chances of finding life on Mars and future human exploration.
The research is based on an analysis of images taken from the American space agency Nasa's Mars Reconnaissance Orbiter spacecraft.
NASA's journey to Mars | Source: NASA
NASA is developing the capabilities needed to send humans to an asteroid by 2025 and Mars in the 2030s.
The agency says that Mars "is a rich destination for scientific discovery and robotic and human exploration as we expand our presence into the solar system".
It is thought its formation and evolution are comparable to Earth, and will help us learn more about our own planet's history and future.
NASA says Mars had conditions suitable for life in its past.
"Future exploration could uncover evidence of life, answering one of the fundamental mysteries of the cosmos: Does life exist beyond Earth?", NASA says.
Robotic explorers have studied Mars for more than 40 years, and NASA's path for human exploration of Mars has beguns in low-Earth orbit aboard the International Space Station (ISS).
"Our next step is deep space, where NASA will send a robotic mission to capture and redirect an asteroid to orbit the moon", it adds.