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NASA\u2019s Perseverance rover is busy exploring the Martian surface and collecting samples for eventual return to Earth. But the rover recently took some time to gaze upward and observe the heavens. Using Mastcam-Z, the rover\u2019s primary science camera, Perseverance captured Phobos, Deimos, and Mercury as they transited in front of the Sun. <\/p>\n
<\/p>\n Phobos and Deimos are unusual. They\u2019re lumpy and are often referred to as \u2018potato-shaped.\u2019 They\u2019re quite close to their planet as moons go, and they\u2019re most likely captured objects, either asteroids or chunks of debris from the Solar System\u2019s early days. They\u2019re also small for primary moons, and both are tidally locked to Mars.<\/p>\n They share the same composition as carbonaceous chondrite asteroids and also have low albedoes. Both those traits bolster the captured asteroid argument. Phobos has the more unstable orbit of the two, and that reflects a more recent capture. Some think that Phobos and Deimos may have been a single object that only broke into two when it was captured. <\/p>\n But, some aspects of Phobos go against the capture theory. It contains some of the same phyllosilicate minerals that Mars does. This points to an alternate formation. A powerful impact could\u2019ve lofted Martian debris into orbit, and the debris could\u2019ve coagulated together to form the small moon. That may have been how Earth\u2019s Moon formed. <\/p>\n On the other hand, both moons have circular orbits near the Martian equator. That hints at a more complex past, including an impact or the involvement of a third body. <\/p>\n The animation below shows Phobos transiting in front of the Sun. <\/p>\n