Solar eclipses on Earth happen a couple of times a year on average. On Mars? The red planet’s moon Phobos can cast a shadow several times a day.
Last month, NASA’s Curiosity rover pointed its Mast Camera (Mastcam) at the Sun to capture Mars’ pair of moons passing in front of our star. Here’s Phobos passing in front of the Sun on March 26.
Here’s Deimos doing the same several days earlier.
A total eclipse is never happening for Mars since the pair of moons are too small. In Phobos’ case, scientists dub it an annular eclipse. Deimos is downgraded to just a transit since it’s so tiny. It looks similar to how a Mercury transit appears from Earth. Speaking of Mercury transits, the next one will be visible for most of North America on November 11. Be sure to catch a glimpse because the next Mercury transit isn’t coming until 2032.
Besides making for a special image, these Martian solar eclipses also help scientists get a better handle on the moons’ orbits.
“More observations over time help pin down the details of each orbit,” said Mark Lemmon (co-investigator for the rover’s Mastcam). “Those orbits change all the time in response to the gravitational pull of Mars, Jupiter or even each Martian moon pulling on the other.”
When a NASA rover first tried to image a solar eclipse back in 2004, scientists noticed Deimos was 25 miles away from where they were expecting it to be. NASA’s three Martian rovers (Spirit, Opportunity, and Curiosity) have seen Deimos transiting the Sun eight times. That number balloons to about 40 for the larger Phobos.
With each eclipse, scientists back on Earth get better measurements for the orbits of the pair of moons. But the gravitational tug of war between the moons themselves and Mars means there will always be a little uncertainty. Plus, Phobos’ days as a moon are numbered.
Here’s one more GIF showing the Phobos’ shadow passing over the Curiosity rover.