Last week, Curiosity outfitted its high-resolution camera with protective filters and took pictures of the sun as Phobos, one of Mars' two small moons, sailed by.

It was a tricky shoot. Phobos and its sister moon Deimos are closer to Mars than our moon is to Earth, so they shoot across the sky relatively quickly. Phobos takes less than eight hours to circle Mars. Deimos takes about 30 hours to make the trip.

Last Thursday, the moons started to cross paths.

"Phobos grazed the edge of the sun, as seen from Curiosity. We had basically a partial eclipse," astronomer Mark Lemmon, with Texas A&M University, told reporters during a conference call on Wednesday.

The rover took more than 600 images with its left and right cameras, about 100 of which captured some part of the eclipse. Not all the pictures have been radioed back to Earth.

Curiosity has a partner in the project. From the other side of the planet, the rover Opportunity was expected to try to shoot the eclipse on Wednesday.

Aside from pretty pictures, the images should help scientists learn more about Mars' internal structure. Like Earth's moon, Mars' moons have some gravitational pull that slightly change the planet's shape.

"That in turn changes the moons' orbits -- Phobos is slowing down, Deimos is speeding up, like our moon," Lemmon said. "This is something that happens very slowly over time."

In 10 million to 15 million years, Phobos is expected to be so close to Mars that it will be torn apart by the planet's gravity.

The moons' passages by the sun, captured by NASA's rovers, help scientists nail down their orbits and determine how fast they are changing. That information in turn is used to assess how much Mars is deformed as the moons go by.

Curiosity resumed skywatching on Tuesday, when both moons passed overhead.

"This was a really hard thing to do. The timing was very precise," Lemmon said.

The next Martian eclipses will take place in about 11 months. By then, Curiosity should be in a better vantage point.

The rover's eventual science target is a three-mile- high mound of sediment rising from the floor of the Gale Crater impact basin where Curiosity landed six weeks ago.

(Editing by Kevin Gray; Editing by David Brunnstrom)

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