We heard a lot about commercial space travel in 2012, but for me the first half of 2013 has been all about commercial space travel to Mars. Audacious ventures like Dennis Tito's Inspiration Mars, which aspires to send a married couple to the red planet by 2018, and Mars One, an effort to colonize Mars by 2023, are all hampered by significant challenges. And yeah, they might be a little bit crazy. But they've also contributed to what I see as a growing public interest in space travel, and a fascinating dialogue about the limits (or lack thereof) of human exploration. There's been a lot written on the topic of human travel to Mars, but my very favorite—and a series I think too many people have missed—is Kate Greene's Mars On Earth adventure at Discover Magazine's website. I mean, she's living in a NASA-funded Mars simulation on Hawaii's Mauna Loa volcano for 120 days. Go read that. —Katie Drummond, The Verge (@katiedrumm)