NPR: Joe Palca

NASA has pulled the plug on one of its two Mars rovers. Spirit hasn't been heard from in more than a year, and now the space agency says it's abandoning hope that it will hear from the rover again.

Any disappointment that Spirit's mission has come to an end has to be tempered by the fantastic success of the robotic explorer. Intended to last 90 days, Spirit operated in Gusev Crater on Mars for more than six Earth years.

Indeed, just landing safely on Mars has to be considered a success, since the red planet has a way of devouring space missions.

Last April, a volcanic eruption in Iceland sent a cloud of ash billowing toward Europe. That ash was potentially hazardous for aircraft, and authorities decided to ground all flights — inconveniencing tens of thousands of travelers — rather than risk an accident. A new study suggests that this was the right decision.

Susan Stipp, a professor of nanotechnology at the University of Copenhagen, was one of the people whose plans were frustrated by the volcanic cloud. She had colleagues who needed to get home to Denmark, and samples were delayed en route from Scotland.

News that air traffic controllers had fallen asleep at their posts has brought a chorus of outrage. But if you think it's easy for humans to stay awake and vigilant when working in the middle of the night, think again. The truth is, there's no one-size-fits-all answer for making sure nodding off never occurs.

The problem is humans aren't nocturnal, but modern society demands some people work at night. So is there anything people can do to be certain they stay awake during the graveyard shift?