Perseverance Photographs Aug. 13 Martian Solar Eclipse by Phobos, a Day After Earth's Total Eclipse

Q: How does a tiny, doomed moon create a solar eclipse on Mars that rivals our own planet's celestial shows?

Phobos creates a Martian “solar eclipse” through geometry, not size. Though the moon is tiny—about 22 kilometers across—it orbits extremely close to Mars, roughly 6,000 kilometers above the surface, so from Perseverance’s viewpoint it can pass directly across the Sun and block part of it. The effect is impressive but not truly equal to Earth’s total eclipses. From Mars, the Sun appears about 0.35 degrees wide in the sky, while Phobos appears only about 0.14 to 0.20 degrees across. That means Phobos is too small in apparent size to cover the Sun completely. What Perseverance recorded on Aug. 13 was therefore a transit or partial solar eclipse, not a total blackout. What makes the event striking is how fast and alien it is. Phobos circles Mars in just 7 hours 39 minutes—faster than Mars rotates—so it rises in the west, sets in the east, and can race across the Sun in around 40 seconds. Its irregular, lumpy shape also gives the eclipse a jagged outline unlike the smooth disk of Earth’s Moon. Phobos is also “doomed” because tidal forces are slowly dragging it inward by about 2 centimeters a year. Scientists expect it to either break apart into a ring or crash into Mars in tens of millions of years. Beyond the spectacle, these observations help refine Phobos’ orbit and deepen understanding of Mars’ moon system. Perseverance’s image matters because it gives humanity a surface-level view of a celestial event on a world no human has yet visited.

Q: Why did NASA's Perseverance pause its search for ancient life to photograph a fleeting shadow cast by a dying Martian moon?

NASA paused Perseverance’s life-hunting work because the eclipse was both scientifically useful and exceptionally time-sensitive. A Phobos transit lasts only seconds, and if the rover does not turn its cameras at exactly the right moment, the chance is gone. The image was not just a scenic detour. Watching Phobos cross the Sun helps scientists refine the moon’s orbit and track how the Mars system is evolving. That matters because Phobos is unusual: it orbits only about 7 hours 39 minutes from lap to lap, passes over the Martian sky frequently, and is slowly spiraling inward toward Mars. Repeated transit observations help researchers better model that motion and the moon’s long-term fate. Perseverance was also built to do more than geology. Its Mastcam-Z cameras regularly support atmospheric and astronomical observations alongside the rover’s main mission in Jezero Crater, where it is searching for evidence that Mars once hosted habitable conditions and possibly microbial life. Briefly interrupting rock studies for a rare celestial event is a normal and efficient use of the rover’s tools. There is also a broader scientific and public value. No humans have ever stood on Mars, so robotic missions provide the only direct surface view of events like this. Perseverance’s image offered a firsthand look at a familiar phenomenon from an alien world, one day after a total solar eclipse was seen from Earth, while adding real data on Phobos and Mars’ dynamic sky.

3 articles · Updated · Space.com · Aug 19

Aug. 13 images from NASA's Perseverance rover captured a partial solar eclipse on Mars, showing Phobos crossing the sun through the rover's left Mastcam-Z camera.
Phobos — the larger of Mars' two moons, Phobos and Deimos — appears to be the body obscuring part of the sun, creating the eclipse seen from the Martian surface.
The sighting came 1 day after Earth's Aug. 12 total solar eclipse, underscoring that solar eclipses can occur on any planet with at least one moon.
Perseverance's photos offer a rare surface-level view humans cannot yet witness directly, extending robotic exploration's role in showing phenomena across the solar system.