Because of its small size, Phobos does not fully cover the sun as seen from the surface of Mars, so the solar eclipse is what's called a ring, or annular, type, NASA's Jet Propulsion Laboratory in Pasadena, Calif., said.
Curiosity paused during its exploratory driving to record the sky-watching images Aug. 17, JPL said.
"This event occurred near noon at Curiosity's location, which put Phobos at its closest point to the rover, appearing larger against the sun than it would at other times of day," said Mark Lemmon of Texas A&M, a member of the team operating Curiosity's Mastcam camera that captured the images. "This is the closest to a total eclipse of the sun that you can have from Mars.
"This one is by far the most detailed image of any Martian lunar transit ever taken, and it is especially useful because it is annular, he said.
Observations of the Martian moons Phobos and Deimos by Curiosity and by the older but still-active Mars rover Opportunity are helping researchers get more precise knowledge of the moons' orbits, JPL said.