OrbitalHub

On 12 August 2026, on the 1,948th Martian day of its mission, NASA’s Perseverance rover stopped what it was doing for a few minutes, pointed its Mastcam-Z camera at the Sun, and watched Phobos, the inner of Mars’s two moons, slide across the solar disk. The animation that came back has been colorized to mimic what a person on the Martian surface would have seen looking up through a pair of protective eclipse glasses: a small, dark, lumpy silhouette gliding across a glowing orange Sun, never covering enough of it to qualify as a true eclipse (Sci.News).

A partial transit like this is small in the moment and large in the long run. Perseverance has been recording these crossings since it landed in Jezero crater in February 2021, and the team keeps shooting them because each one is a measurement of where Phobos is, and where it is going. By comparing the recordings taken years apart, scientists can refine the moon’s orbit, watch how the orbit is decaying under Mars’s tidal pull, and update the timeline for the day Phobos will finally break apart at the Roche limit or crash into the planet (Sci.News). The same kind of observation, applied to a star instead of a moon, was how exoplanet hunters in the Kepler and TESS era measured the size and orbital period of worlds around other stars. Phobos in front of the Sun is the equivalent demonstration, just two doors down from Earth.

The other reason the recording matters is that Phobos is one of the few Solar System bodies small and close enough that a single orbiting spacecraft can resolve its shadow path from the surface. The moon is only about 26 by 22 by 18 kilometers across, smaller than many asteroids, and orbits Mars at roughly 6,000 kilometers from the surface. That closeness is also why the transit never becomes a total eclipse: from the Martian surface, Phobos never appears large enough to cover the Sun’s disk, only to carve a moving bite out of it.

The 12 August 2026 observation was Perseverance’s most recent entry in a routine the rover has been keeping for more than four Earth years. The Mastcam-Z instrument, a pair of zoomable color cameras mounted on the rover’s remote sensing mast, has been used on multiple earlier sols to record Phobos and Deimos transits. Each observation produces a short video of frames that the team can stack, time-stamp against the rover’s onboard clock, and compare with prior sessions.

What is new with sol 1948 is mostly cosmetic. The animation was tinted on the ground to simulate the visual impression a human observer on Mars would get looking up through solar-eclipse glasses, the same orange-tinted look eclipse chasers use on Earth. The raw data is still a time series of dark silhouettes moving across a bright source. The team released the public-friendly version after running the standard calibration, and the Sci.News writeup on 24 August pulled it back into the news cycle as part of a steady drip of small Mars-science updates (Sci.News).

Behind the video is the same physics that makes a solar eclipse work on Earth: a foreground object passes between the observer and the Sun, casting a moving shadow. The differences are size and geometry. Phobos is roughly 150 times smaller than Earth’s Moon and sits about 200 times closer to Mars than the Moon does to Earth, so its angular size is far too small to cover the Sun. The Moon’s apparent diameter almost exactly matches the Sun’s during a total solar eclipse on Earth, which is the happy coincidence that makes totality possible. Phobos never gets that close to covering the Sun, so the term “transit” is the right word, with “annular eclipse” reserved for a slightly bigger blocker that still falls short of totality.

Mastcam-Z is the workhorse camera on Perseverance’s mast, sitting about two meters above the Martian surface at the eye level of a roughly 6½-foot-tall person, with the two cameras separated by about 24 centimeters to give stereo vision (NASA Mars 2020 Mastcam-Z page). It was designed primarily to study rocks and soils from a distance, with a zoom range that lets the team build topographic maps of terrain features, and it can record 1600 by 1200 pixel frames at up to about 148 megabits per sol of returned imaging.

The transit record itself is what the orbital dynamicists want. Phobos orbits Mars in 7 hours and 39 minutes, faster than any other moon in the Solar System relative to its parent planet’s rotation, and tidal drag is slowly shrinking that orbit. The standard textbook figure is that the orbital radius is decreasing at roughly two centimeters per year, or about two meters per century, and the projections for when Phobos will either break up into a ring or crash into the surface run from about 30 million to 50 million years out (Wikipedia: Phobos (moon))). Observations like the sol 1948 transit tighten the numbers behind those projections by giving the orbit a fresh astrometric fix.

The geometry also gives a measurement that is hard to get any other way: from a fixed landing site like Jezero, the exact path of Phobos across the Sun depends on where Phobos is in its orbit at a particular second. Cross-referencing that path against time, the rover team can solve for orbital elements that mass and remote sensing measurements cannot constrain.

A subtle point worth flagging is that Perseverance did not move to capture this transit. The rover was wherever it happened to be on sol 1948, and the team aimed the mast at the Sun from there. This matters because location is one of the unknowns in the orbital fit: if Jezero’s coordinates are even slightly off in the Mars-fixed reference frame, every recorded shadow path inherits that error. Years of persistent observations from the same rover at the same site cancel most of that error out.

The 12 August 2026 Phobos transit is a small piece of work by a long-running rover that has already spent more than five and a half years on Mars. The Mars 2020 mission’s headline job, caching samples for a future return mission, is well into its second decade of planning, and Mastcam-Z observations of this kind are now a small but reliable side-product that keeps adding data to the Phobos literature. Expect another of these recordings every few months from Jezero as long as the rover stays healthy, and the public versions appear in the standard NASA Mars 2020 image release channels over time. The longer-running payoff sits in the orbit itself: each transit shaves uncertainty off the prediction for the day Phobos stops being a moon.