In Britain the Royal Mail
created a special postmark to celebrate Philae's landing on the comet. It would be applied to anything mailed on November 14, 15 or 17. Great idea, I thought. I have a friend who collects astronomy-related stamps, and although this wasn't exactly a postage stamp, it still seemed rather special. So I popped a card in an envelope and mailed it.
Boo, Royal Mail! It arrived pristine at its destination. Not a single mark on the envelope except where I'd addressed it. Sigh.