During my thesis defense, one of the questions that caught me most off guard was: “What would you say to a member of the public who asked you why we’re spending more than $2 billion on the Mars Science Laboratory rover?”

I’m ashamed to say that I didn’t answer very well. I was all prepared for my research methods and results to be picked apart, and so I went sort of brain-dead when this question came up. Now, with the brutal cuts to the planetary science budget in the president’s proposed budget for fiscal year 2013, I think it’s time I gave a proper answer.