T/F: Water once flowed on Mars.

Mars geology is truly fascinating and plays a key role in understanding the planet's history, especially its relationship with water. Mars has various geological features that suggest it was once much wetter than it is today. These include:
- Valley networks
- Outflow channels
- Gullies

These formations are similar to those created by flowing water on Earth. The presence of these features shows that liquid water once shaped the Martian surface. Additionally, scientists have discovered minerals like clays and sulfates, which typically form in the presence of water. These geological clues are critical because they help researchers piece together Mars' climatic history and understand if conditions were ever suitable for life.

Mars missions have been instrumental in uncovering the secrets of water on the Red Planet. Several missions launched by NASA and other space agencies have provided compelling evidence:
- **Viking 1 and 2**: Launched in the 1970s, these landers sent back images of landscapes that suggested the past presence of water.
- **Mars Global Surveyor**: In the late 1990s, it mapped the Martian surface, revealing dried-up riverbeds and signs of ancient lakes.
- **Mars Odyssey**: Detected substantial amounts of hydrogen just below the surface, indicating the presence of vast quantities of ice.
- **Mars Exploration Rovers (Spirit and Opportunity)**: These rovers found various types of rocks and minerals that form in water.
- **Mars Reconnaissance Orbiter**: Provided high-resolution images that showed recurring slope lineae, which might be due to flowing salty water.

Each mission has built on the findings of the previous ones, painting a clearer picture of Mars as a planet that once had water actively flowing across its surface.

The evidence of water on Mars is now overwhelming thanks to various studies and missions. Some of the most compelling pieces of evidence include:
- **Dried-up riverbeds and valley networks**: These are striking indications that liquid water once flowed across the Martian surface in large quantities.
- **Minerals that form in water**: Discoveries of clay minerals, sulfates, and other hydrated minerals from rover analyses show that Mars had long-term liquid water activity.
- **Polar ice caps**: Mars has polar ice caps composed mainly of water ice, further proving that water exists on the planet.
- **Subsurface ice**: Data from orbiters and landers have confirmed the presence of ice just below the surface in various regions.
- **Gullies and slope lineae**: Formation of gullies and seasonal dark streaks on slopes suggests recent activity of liquid water, likely briny (salty) water.

All this evidence strongly supports the idea that Mars was once a much wetter planet, capable of sustaining liquid water for extended periods.