Astronomy questions

1) Give two arguments for life having existed on Mars. Do you agree with these? Why or why not?

2) What is the greenhouse effect? Could a mild greenhouse effect help make a planet habitable? Explain.

3) Give one method to infer the presence of an exoplanet by observing its host star. How reliable do you think this method will be? Was Kepler’s third law used at any point in this process? Explain.

4) Are there seasons on Mars? How do we know? Explain how there can be so much water present and yet very little to none is present on the surface.