Divide your group into two subgroups. After a few minutes of preparation, have one subgroup present the evidence used in Percival Lowell's time to demonstrate the likelihood of life on Mars. Let the other subgroup huddle for a minute and then try to refute the evidence of the first subgroup based on more recent information.
With your group, prepare a plan for what you would need to take along in order to survive 6 months on the Martian surface. If possible, make a brief presentation of your plan in class. Invite the class to discuss whether recent discoveries of ice on Mars would have any impact on your plan.