One day, while comparing different satellite images of a single Martian crater taken at various times of year, he noticed something odd: a set of dark streaks in the soil that grew in the Martian summer and shrank in the winter. They seemed to flow down the crater's slope, like a spill.

It took NASA a few years to gather more evidence after the student made his report, but finally, in September of 2015, the agency called a big press conference. It confirmed what the undergraduate had suspected almost right away: That was water in that crater.

Back in the 1970s, NASA scientists had informed everyone that the Red Planet was a dry, barren, dead place. Whoops. Now a new generation of NASA scientists were on a dais in Washington, DC, musing openly about what this new finding meant for the odds of discovering life on Mars. "When you look at Earth, everywhere we go where there's liquid water," said Jim Green, the agency's director of planetary science, "we find life." And the Martian water wasn't confined to that one crater wall. Once scientists knew what to look for, they found similar dark streaks at more than a dozen other sites. The agency's Curiosity rover was actually within striking distance of a few of these streaks. "We might be able to visit," Green said. The announcement made headlines around the world. It also set off a bunch of quiet changes within the space agency itself.

When you look outside of the window of a plane, if you are high enough, you can see the curvature of the Earth. Having seen this first hand, I think it justifies the roundness of the Earth without relying on third-party info.