How to develop research topic in oversaturated field?

[GirtonOramsay]

I am fairly certain that I want to attend Idaho, but I have this "mental barrier" that is making me apprehensive to fully commit since I feel I won't find viable research topic(s), given my specific circumstances. In my case, I have all of the usable data sets available to me (from an expired satellite mission), but the data has been scoured over for many years to the point that all of my ideas have already been done by other researchers. I read the literature (for ~3 months now) and get overwhelmed since I can't find any good ideas that haven't been explored yet. My POI has assured me that there is plenty of available problems to get a PhD, but I still remain uncertain of my capabilities. I just have this feeling that I won't be able to make an impact with my lack of confidence in my ideas now, but I also may be making overly high expectations for myself too.

In general, what are some things that I can do to develop research ideas with advice and feedback from my POI during my first year? Should I rely on my POI to just give me some ideas to test out for the first year? 

[TakeruK]

Your advisor is likely right---in our field, there ARE tons of valuable insights that remain to be made from the precious data, especially data from missions! For most of these missions, even when they have ended, the existing dataset is going to be the best data available for a good long while. It takes so much time, energy and especially money to get missions to other planets/moons and there are just so many cool places to see in our Solar System that unless you're studying Mars, there may only be one mission (two if you're lucky) to your favourite celestial location in your career. 

You are also right that you should be working with your advisor during your first year(s) to develop projects into a PhD. I don't mean to insult you but it's not that worrying that a prospective grad student is unable to come up with ideas that haven't already been done by other researchers. If you can do this, then you would already have a PhD  The reason why it is hard for your specific case is that with missions, the "low hanging fruit" and the most obvious studies to conduct are done first. In fact, they are often already planned by the science team years before the mission even launches (of course, the missions themselves yield data that leads us in more directions!). So, in your shoes, I would not worry that I can't come up with a novel way to analyze the data that the rest of the field has not already considered. There is way more data out there than people in our field to work on it and your advisor can help you carve out a niche for yourself. 

I consider grad school to be an "incubation" process to becoming an independent researcher. At first, you would "rely" on your advisor more to come up with project ideas. You should definitely still try to come up with your own but it's okay if these ideas are already done by others (in fact, it's a good sign, because this means that your thinking is in tune with the field's). Discussions with your advisor can help you figure out how you can take a different approach than others have in the past. Planetary Science is also a beautifully multidisciplinary field (in my totally unbiased opinion :P) so during your grad studies, you will be meeting other people with different approaches and you will get opportunities to combine something you learned from one area with a dataset from another area to develop new results. In fact, during my grad studies, this happened quite often amongst our students  

As I said, grad school is a training/incubation process. The goal is to leave with a PhD and the ability to not only come up with good ideas for yourself but also some wisdom/experience in knowing which ideas are worth pursuing and how to really refine an idea into an actual project. If you could do all this already, then you wouldn't need a PhD. So don't beat yourself up if you are only at the "ideas" phase (which is already itself a great start).

[GirtonOramsay]

Thanks a lot for the great advice and insights on planetary science TakeruK! I agree that I really like the inter-disciplinary nature of planetary science and pursued my undergrad to learn many Earth science disciplines to be prepared for this field. You have a good point that I've put too much pressure on myself to think that I need my dissertation topic before entering grad school, but it's reassuring that having a good background in the field has put me "a step ahead" with potential ideas.