The strange sight of a solar eclipse on Mars

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NASA’s Curiosity rover saw two solar eclipses on Mars in March.

On Earth, total solar eclipses are spectacular events. But they’re the result of a total coincidence: The moon in the moments it passes between Earth and the sun is just the right size to cover the sun completely from where we stand. It blots it out, revealing the sun’s atmosphere, the great glowing solar corona.

There’s no scientific reason for this. We’re just lucky.

In March, NASA’s Curiosity Rover got to witness two solar eclipses of the red planet.

The most striking one was the Martian moon Phobos, which sped by Mars on March 26. Unlike on Earth, the moons of Mars do not completely blot out the sun. Instead, they appear as smallish, potato-shaped objects transiting across the surface of the sun.

Here’s what the rover saw on March 26, as the Martian moon Phobos crossed the face of the sun.

The image of Phobos was taken with Curiosity’s Mast Camera, with a special solar filter attached (kind of like the solar eclipse glasses you’d use to look at the sun on Earth). NASA just released these images Thursday.

 NASA/JPL-Caltech

On March, 17, the much smaller moon Deimos made a much slower crawl past the surface of the sun. It’s more of a “transit” of the sun than an eclipse, but still quite neat.

 NASA/JPL-Caltech

Mars’s two moons — Phobos and Deimos — are small and distinct from our moon. Phobos, the larger of the two is just 16 miles across.

But what it lacks in size, it makes up for in speed. Phobos is caught in a very fast orbit around Mars, completing a revolution in about eight hours. That means it rises and sets multiple times on a typical Martian day (which is about 37 minutes longer than ours). Phobos is also incredibly close to Mars — orbiting at a distance of 3,700 miles. Our moon is 239,000 miles away. Deimos is even tinier, about 8 miles across, orbiting Mars once every 30 hours.

On Mars, there’s a solar eclipse nearly every day. The Martian moon Phobos’s orbit is nearly directly over its equator; our moon, on the other hand, is in a tilted orbit, so the Earth, sun, and moon don’t line up as often. And this isn’t the first time Curiosity has captured images of solar eclipses on Mars. But the images are important because they help scientists better understand the motion of Mars’s moons.

 ASA/JPL-Caltech/Malin Space Science Systems/Texas A&M University
The size of Phobos and Deimos, compared to the size of our moon.

The rover captured the recent eclipses because observations of the eclipses help scientists understand Mars and its moons. Phobos, for one, is expected to keep dipping closer and closer to the surface of Mars, due to tidal forces.

“More observations over time help pin down the details of each orbit,” Mark Lemmon, the NASA co-investigator in charge of the Mast Cam, said in a press statement. “Those orbits change all the time in response to the gravitational pull of Mars, Jupiter or even each Martian moon pulling on the other.” Watching them move across the sun helps NASA figure out orbits of the moon.

It’s also just cool. Curiosity was also able to see the shadow of Phobos as it passed over the sun. This is what it looked like.

 NASA/JPL-Caltech