A fresh picture from NASA's Curiosity rover shows the Martian moon Phobos as it's never been seen before — as a crescent shining over the Red Planet at dusk.

The image was captured by the rover's Mastcam imaging system last Friday, on the 45th Martian day of Curiosity's mission. You have to look closely to make out the faint, somewhat irregular crescent in the frame — just as you sometimes have to look closely to see our own moon's ghostly crescent in Earth's daytime skies.

We've seen other views of Phobos, the larger of Mars' two moons. But those mostly show the moon as seen by Red Planet orbiters, or as a silhouette during an eclipse. This is a rare photo (perhaps the first?) showing a crescent moon in a daylit Martian sky, as seen from the surface. It's the sort of spectacle that settlers could look forward to at sunset, decades from now.

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The Planetary Society's Emily Lakdawalla provides further detail in her blog posting, plus further reflection: "Think about this for a moment — we're seeing a different moon from the surface of a different world. And this moon is weird not just for its lumpiness, but also because it orbits so close to Mars that it outpaces Mars' rotation. That means it rises in the west and sets in the east, more than twice every Martian day. Completely alien. And awesome, in the literal sense of the world."

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