What you need to know is that graduate school is a must. Not many employers who hire geologists hire BS geologists for anything other than field tech or lab tech work. You need a Masters degree to be a "professional" that is someone who works solving problems. You need to know that companies are in business to make money. If you cannot do that for them, they are not much interested in hiring you. So, you need to be a problem solver and that is what a MS degree and thesis work does, it teaches you to solve problems. A BS merely in most cases just fills up your intellectual tool box with concepts and knowledge, but you do not really know how to apply them. Thesis and dissertation work teaches you how to identify and solve problems.
Okay, so you want to be a Interplanetary Geologist, the first thing you need to do is determine what area, petrology and mineralogy, or land forms, sedimentary bed forms and sedimentology in general.
My friend is a senior PhD Geologist at the Jet Propulsion Laboratory in California and had a key place on the team for the Mars landers. He devised several of the soil and rock sampling tools on the Rovers. The rover is equipped with instrumentation that can send data back on the mineralogy petrology of the rocks and soil. However a lot of the information sent back is merely imagery. That is where the interpretation of the various bedforms and landforms comes in. The remote sensing geologist must be able to interpret and analyze images to tell him what processes laid down the sediments and rocks from the indicative structures and forms he can discern on the satellite images or images taken by the rover scanners.
So if he sees a type of bedding or cross bedding in a picture he knows the sediment in the rock was laid down by water or wind, or volcanic activity, or even a meteor strike.
So, when you make you choice of college, be sure that there are professors there teaching that can teach you what you need, and have the same interests. Many time students just get into a program, not knowing what they want, and end up following a professor into HIS area of study, which may or may not be what they want or something they can even get a job doing.
If you can find a program or professor with those interests, chances are he has contacts at NASA and can assist bright students of his to get internships.
With the focus on Mars, an MS Thesis, and a Doctoral Dissertation on Mars Geology would be a big step in getting a foot in the door considering Mars seems to be the focus of NASA for the forseeable future. Anyone who has deep research knowledge on aspects of Mars Geology will no doubt have a great advantage over other applicants, especially if you can land an intership.
If I were you, I would do my reading and catalog all those geological topics, technology and geographic areas on Mars that the current exploration has identified as areas of interest. This would give you a listing of those topics to consider for your future college research work. They you will graduate as an expert in those areas.