Mars is the 4th planet from the sun. Many attempts to replicate Mars' environments or explore Mars have been made over the years. It is one of four planets that scientists believe to be in the "goldilocks zone of the solar system." NASA has sent many robots, or Rover's, to explore and document Mars.
The many different robots scientists send to Mars collect data like the miles traveled, screenshot and send images of its findings on the surface, document the steepest slope it went down, as well as other things. The size and lifespan of these robots usually depend on how much information the scientist wants to gather, or just what resources they have at the time. These robots are very important for getting information about Mars that would only otherwise have been gathered by humans. Scientists use the information from the robot's findings and use them to test hypothesis' about Mars, and also figure out how, when, and where to land to send humans to the surface of Mars.
There has been a lot of evidence gathered from the many Rover's sent over the past few decades that support the idea that there once was life on Mars. Rover's such as the Curiosity, Opportunity, and Perseverance Rover's have likely all found evidence of past life on Mars through different chemicals and minerals. The type of life the scientists found out existed were microbes.