Summary:

- The article discusses the discovery of wave ripples on the surface of Mars, which suggest that liquid water was present on the planet's surface around 4 billion years ago.
- These wave ripples were observed in images captured by the HiRISE camera on NASA's Mars Reconnaissance Orbiter, and they are similar to those formed by the movement of water on Earth.
- The presence of these wave ripples provides evidence that Mars once had a wetter and more Earth-like environment, which could have supported the development of life on the planet in its early history.