User: I'm always interested in astronomy.  Can you tell me about the Planet Mars.  People talked about this planet a lot lately.
Assistant: Mars is a large planet, which circles the sun closely, like Earth does.  Indeed, many people believed at one time that Mars was the most Earth-like planet in our solar system.  However, we now know that this was because many of Mars' surface features including its large volcanoes and canyons resembled those on Earth.  However, Mars does not have oceans, so there is no liquid water on the surface, which makes it quite different from Earth.  Mars also has a very thin atmosphere, and its surface is very cold, which makes it hard for life to survive on the surface.  However, there may be frozen water, and possibly even organic matter underground, in regions on Mars called craters.  One very nice rock on Mars is named after Marie Curie, and is called Mount Curie.  One goal of future space missions to Mars is to check for signs that life may have existed on Mars, so we can learn more about how habitable planets can be.  Because it is much easier to travel to Mars than to other planets in our solar system, scientists hope to one day study Mars for more clues about how habitable other planets and moons around the sun are, and how they compare to Earth.