Saturn Photobombs Show New Images of Mars Moons Phobos, Deimos

New images of Mars’ two moons, Phobos and Deimos, could help shed light on how the mysterious rock operates in their orbit.

The photos, which the European Space Agency released this week, show the moons’ cratered surfaces and gave scientists a chance to update calculations about how they are positioned in the sky.

Because Phobos and Deimos always show the same face to Mars—known as being tidally locked—a spacecraft has to make multiple passes in order to capture all the details of the surface, which are crucial for understanding how the moons formed and what they are made of. According to the ESA, the new images have offered a closeup of “the bumpy, irregular and dimpled surface” of Phobos and the “irregular and partially shadowed body” of Deimos.

The agency’s Mars Express spacecraft snapped the new images of Phobos and Deimos in January.

Of the two moons, Phobos is larger and closer to Mars; it is 17 miles across and orbits the Red Planet three times a day. Deimos is 9 miles across and takes 30 hours to make a revolution.

Deimos_and_Saturn Saturn looms behind Deimos, the smaller of Mars’ two moons. ESA/DLR/FU Berlin

“There is much we still wish to know about the Mars system,” the space agency explained. “The moons remain particularly mysterious, with open questions about their origins, formation and composition. As a result, combined with their proximity to the Red Planet, the little moons have generated a lot of interest as a target for future missions.”

The photos of the moons were special not just for their main focus, but the space behind them was important as well. That includes Saturn, which helped out astronomers from several hundred million miles away.

As the ESA pointed out, “Scientists repeatedly refine our knowledge of the moons’ positioning in the sky and ensure it is up-to-date by observing each moon against background reference stars and other solar system bodies.”

In the new shots of Deimos, the outer solar system planet lurks in the background, a ringed smudge of light in the blackness of space.

Having more precise measurements of the moons’ positions makes it easier to study them further, because sometimes a spacecraft only has a few moments to line up a shot and take it.

Phobos_and_background_star A background star (circled) offers a reference point for scientists studying Phobos, the larger of Mars’ two moons, in this January 2018 photo. ESA/DLR/FU Berlin

Phobos_surface_sequence A sequence of images the Mars Express spacecraft took of Phobos, the larger moon of Mars, in September 2017 shows the cratered surface. ESA/DLR/FU Berlin

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