Not too easy. Not too difficult.
It's an easy elective as long as you do well on the exams. I would recombined not buying the book, and focusing only on slides provided. All the exam questions are from the slides, but the professor focuses on small details from the slides, so its important to read them carefully.
I did not know too much about the solar system, so it was an interesting topic to learn about, if you're not averse to learning about planets for an entire semester. The sole purpose of the course asks the question: can life be sustained somewhere besides Earth? The course is very organized, going from planet to planet, sometimes moons as well, asking this question.
Hours per week:
Advice for students:
As mentioned before, don't buy or rent the book. I hardly used it, and it's not necessary. To study for exams, I would recommend reading the slides thoroughly multiple times.