Mars Moons Double Eclipse
August 16, 2013

Curiosity Captures Pics Of Mars’ Double Lunar Eclipse

Brett Smith for - Your Universe Online

NASA has just released a series of images from its Curiosity rover depicting Mars’ largest moon, Phobos, passing in front of its smaller counterpart Demios. The images have been assembled into a video available on the space agency’s website.

Taken from the surface, the images clearly show large craters on Phobos and will be used to refine knowledge of the moons’ orbits around Mars. They mark to the first time the two moons have been seen eclipsing from the Martian surface.

"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 co-investigator for use of Curiosity's Mastcam, which took the photos. "We may also get data good enough to detect density variations within Phobos and to determine if Deimos' orbit is systematically changing."

NASA scientists realized that the two moons could be seen crossing paths at a time just after Curiosity would be available to send data to NASA's Mars Reconnaissance Orbiter to be relayed on to Earth. The convenient coincidence made the observations possible with minimal impact on the rover's energy allotment. Snapping images of the two moons was only a fleeting distraction from the rover’s current mission of looking into the environmental history within Mars’ Gale Crater, a location thought to be favorable for ancient microbial life.

While Phobos is slowly orbiting closer to Mars, the orbit of Deimos is gradually taking it farther from the planet. Phobos, the larger moon, has a diameter less than one percent of our own moon’s diameter. It also orbits much closer to Mars than Earth’s moon – appearing approximately half as wide in the sky as our own natural satellite.

Named after the Greek god of fear, Phobos is an irregularly-shaped moon with a surface area roughly equivalent to the state of Delaware. Previous research has suggested that the moon is not completely made of solid rock and could hold a sizeable reservoir of ice. Images taken from the Mars Global Surveyor indicate that Phobos is covered with a loose layer of dust and broken rocks called regolith that is over 300 feet thick.

Named after the Greek god of terror, Demios also has a highly irregular shape. It is believed to be comprised mostly of carbon-rich material similar to C-type asteroids. While its surface is pock-marked by impact craters, it is much smoother than the surface of Phobos.

Demios’ orbit is highly circular and it approaches the equatorial plane of Mars. Thought to be a ‘captured’ asteroid, a controversial theory posits that Jupiter pushed it toward Mars, eventually causing the moon to adopt a circular orbit around the Red Planet.

At its peak brightness, Demios would only appear as an unusually bright star from the Martian surface – similar to the appearance of Venus on Earth. The phases of Demios take about 1.2 days to complete, and the speed of its orbit means that it rises in the west and sets in the east, unlike Phobos, which rises in the east and sets in the west.