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NASA has actually done this before, for example, you could have sent your name to Mars with the Phoenix rover. However, now that this has been found by Reddit, I'm afraid that that list of names sent to Mars will be an odd one indeed. First of all, there's no captcha, and the form accepts nearly anything, even very long entries.
From Reddit's commenter digitalboy:
"It appears that the input is unbounded. One could then send a somewhat long Base64 encoded binary messages to mars. I'm sure there is SOME bound somewhere but it doesn't appear to be on the form. I create a 4k first name and it took it as input. What to send.... Perhaps a map to my house? Perhaps the lyrics to my favorite song? Fibonacci sequence? Prime numbers? Hm."