The cameras of NASA’s Curiosity rover usually look down at the rocks on Mars, divining clues in the minerals of what the planet was like billions of years ago.
Sometimes the rover also looks up. In March, it spotted two eclipses.
Eclipses on Mars are not quite as total as those sometimes seen on Earth when the moon completely blots out the sun. The two moons of Mars are small: Phobos is 7 miles wide; Deimos is even tinier, just 1.5 miles in diameter. They only partially block the sun when they pass in front of it.
The camera on Curiosity’s mast is equipped with solar filters that allow it to look directly at the sun and photograph eclipses. On March 26, Curiosity observed Phobos eclipsing the sun. Nine days earlier, it also spotted Deimos passing in front.
Although Phobos does not completely eclipse the sun, the Martian satellite does block it enough to momentarily darken the sky. Another camera on Curiosity noticed the dimming of the landscape on March 25 as the shadow of Phobos passed over the rover at sunset.
The observations by Curiosity — and by earlier NASA Mars rovers, Spirit and Opportunity — enable more precise pinpointing of the moons’ orbits, which are jostled around by the gravity of Mars, Jupiter and even each other.
Although Phobos and Deimos are small, the details of their formation are of considerable scientific interest. Japan’s space agency plans to send a spacecraft to the two moons in the next decade. The Mars Moon Exploration probe, or MMX, will collect samples and return them to Earth for study. A panel of scientific experts earlier this week approved the sample-return phase of the mission.
This article originally appeared in The New York Times.