Sometimes, the best part about science are all the still-unanswered questions and the possibilities they offer. And sometimes, you just want an answer already.
Today, we want to know about the unanswered questions that you most want to be figured out while you're still roaming around this planet. Tell us in the comments what the question is and what it is that makes it stick in your mind.
Image: ESA, NASA, and L. Calcada.