Curiosity captures footage of a Martian moon eclipse

For the first time for any Mars surface expedition, the Curiosity rover captures images of two Martian moons eclipsing each other.

Deimos, the smaller of the Mars moons, gets overshadowed by its sibling Phobos. The large recess at the bottom of Phobos is Stickney Crater.

As Curiosity continues to trek across the wild red yonder of Mars, it stopped for a moment earlier this month to observe the two Martian moons, Phobos and Deimos, passing by each other in the night sky. This imagery of one Martian moon eclipsing another as seen from the surface of Mars is the first of its kind, and serves a useful purpose for astronomers.

"The ultimate goal is to improve orbit knowledge enough that we can improve the measurement of the tides Phobos raises on the Martian solid surface, giving knowledge of the Martian interior," said Mark Lemmon, a Texas A&M University co-investigator working with Curiosity's Mastcam. "We may also get data good enough to detect density variations within Phobos and to determine if Deimos' orbit is systematically changing."

Curiosity's Mastcam telephoto-lens camera captured the unique view of the two Martian moons on August 1, but the full-resolution visuals weren't sent back to Earth until a week later as they were considered a low priority transmission.

Unlike Earth's colossal moon, the two moons orbiting Mars are far smaller and have different orbits. For starters, Phobos has a diameter of 6.9 miles and is getting closer to Mars, while Deimos is 3.9 miles and is branching farther away. To put things in perspective, Earth's moon is 2,159 miles in diameter. According to NASA, Phobos closer orbit makes the rock appear about half the size as the moon does here on Earth.

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