online education in a short space of time

I've been teaching an online course for my graduate school alma mater for the past several semesters. So far, each semester has been 14 weeks long, with four of the sessions being face-to-face and the other 10 sessions being conducted through a course homepage provided by the school. I've been trying to brainstorm ways to keep the class on-track for covering all the material required, but making the best use of the online format.

Now I'm teaching a shorter summer version of the course that is only going to be four weeks long. Summer courses are supposed to be intensive, but I just can't see proceeding through all of our material in a linear fashion given the time constraints. How to make this a productive experience for the students, and get them to generate enough written work for me to assign a grade?

Here are some options I've been considering:

-Give out the syllabus in class (our first session is face-to-face) but design it to be a non-linear, "choose your own adventure" style experience. Provide the resources and assignments, but allow people to interact with what's provided in the order of their own choosing and contribute to the course forums and debates based on what they've learned for the week.

-Structure the course into the 8 distinct sessions that it would be if the course were conducted in person, but assign or ask students to select which sessions they'll respond to in writing, or provide overarching written assignments that don't correspond to a distinct session.

-Develop one essential question that we'll continually respond to over the course of the semester - responses for each week will take into account what students have gathered over the course of that week's work. How to sum up a survey course in one essential question? That is the question!

I've found in my elementary school teaching, however, that it isn't impossible to do. My 3rd grade science classes spent the entire year on the question "Can life exist on other planets?", a study that encompassed both Earth and Space topics. After all, in order to know if life can exist on other planets, first we have to understand why and how life exists on THIS planet. Everything else flows from that.

So it may be possible to come up with one "big question" that can be the focus of the entire semester - thereby relieving the pressure to come up with multiple different assignments to be completed in such a short time frame.