Martian moon Phobos as it crossed in front of the Sun, as seen by NASA’s Curiosity Mars rover on Tuesday, March 26, 2019.


NASA’s Mars rover Curiosity has filmed two solar eclipses caused by its moons Phobos and Deimos as well as a rare “sunset eclipse”, and the results could be decisive for scientists planning space missions to the Martian moons.

Two solar eclipses on Mars

Last week NASA’s Curiosity Mars rover sent back some spectacular photographs of two solar eclipses caused by its two moons Phobos and Deimos. The images were captured by Curiosity’s telephoto-lens camera, called its Mast Camera (Mastcam) using its right-eye solar filter. The images for Phobos  (left) have been sped up by a factor of 10; the entire eclipse lasted about 35 seconds. For Deimos (below), the images have been sped up by a factor of 10; this “eclipse” (or was it? see below) lasted several minutes.

Just last month NASA’s InSight lander also captured a 27-second solar eclipse caused by Phobos.

Curiosity captures a shadow

NASA’s Curiosity also observed the shadow of Phobos on March 25, 2019; as the moon’s shadow passed over the rover during sunset, it momentarily darkened the light (below).

Are these “real” solar eclipses?

An annular solar eclipse as seen from Earth.


Technically, yes, but to a purist eclipse-chaser, not really. Phobos, which is about 7 miles (11.5 kilometers) across, was imaged on March 26, 2019. It doesn’t completely cover the Sun, so it’s called an annular solar eclipse. Phobos covers most, but not all, of the Sun, creating what’s known on Earth as a “Ring of Fire” eclipse (when our Moon is at apogee – its furthest point from the Earth in its elliptical orbit – so appears smaller in the sky than the Sun). Total darkness doesn’t occur during an annular eclipse, and solar safety eclipse glasses must be worn.

No solar eclipse on Mars can match the majesty of totality as seen from Earth, where the Moon occasionally perfectly blocks the Sun. This image is of the 2017 total solar eclipse. 


Eclipse vs. Transit

Luckily, Curiosity took some along. Deimos is about 1.5 miles (2.3 kilometers) across and was photographed on March 17, 2019. Deimos doesn’t even nearly cover the Sun, so it’s more of a “transit” than an eclipse. That’s an important distinction, but even if Martian solar eclipses are less than spectacular, they are important. From Earth, the next transit viewable will be the Transit of Mercury on November 11/12, 2019, when observers in North and South America will be able to see Mercury as a tiny dot in front of the Sun (though only through a telescope).

Why are eclipses on Mars important? 

Capturing solar eclipses on Mars help researchers fine-tune their understanding of each moon’s orbit around Mars. The first time one of the rovers tried to image Deimos eclipsing the Sun, they found the moon was 25 miles (40 kilometers) away from where they expected. That now makes eight observations of Deimos eclipsing the Sun from either Spirit, Opportunity or Curiosity, and over 40 observations of Phobos. 

Japan’s MMX mission in 2024 will return a sample to Earth from Martian moon Phobos.


Japan’s “MMX” mission to Phobos and Deimos

The exact orbit of Phobos is going to be critical if Japan’s Mars Moons eXploration mission (MMX), which will launch in 2024. The probe will study both Phobos and Deimos, and put a lander on Phobos to take a sample. That sample will blast-off back to Earth to arrive in 2029.

Eclipses make Mars “relatable”

There’s another reason why eclipses on Mars are important. “Eclipses, sunrises and sunsets and weather phenomena all make Mars real to people, as a world both like and unlike what they see outside, not just a subject in a book,” said Mark Lemmon of Texas A&M University, College Station, a co-investigator with Curiosity’s Mastcam.

After all, who doesn’t love a solar eclipse, whatever planet it’s on?

Disclaimer: I am editor of WhenIsTheNextEclipse.com

Wishing you clear skies and wide eyes

Follow me on Twitter @jamieacarter@TheNextEclipse or read my other Forbes articles via my profile page.


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