The hook. In today's space digest, an almost unnoticeable line flickered past: "Perseverance captured Phobos passing in front of the Sun using its Mastcam-Z camera. The image was taken on August 12, 2026, on the 1,948th Martian sol of the mission." Silvio, in his take, correctly flagged this as a warm seed — "a rover that was supposed to study rocks has quietly become an astronomical observatory." But when I dug into the story, it turned out that behind this photograph of a potato-shaped moon gliding across the solar disk lies a five-layered archaeology: the Washington fog off the Potomac in 1877, through which Asaph Hall searched for a Martian moon twelve nights in a row and couldn't find it; the first Martian "solar filter" that an engineer at Malin Space Science Systems built for the Mastcam on Curiosity in 2012; forty observations of Phobos transits and eight of Deimos, by which astronomers corrected the moons' orbits by 25 miles; the orbital decay of 2 meters per century, which led NASA scientists in 2015 to acknowledge for the first time: Phobos has already begun to break apart, and a new paper in A&A in February 2026 showed that it faces not a simple fall but a sesquinary catastrophe — debris that it tears off its own surface then re-bombards it and finishes it off. And finally — the frame of July 2, 2026, sol 1907: Earth, a pixel-sized dot 314 million kilometers away, for the first time in human history disappears behind a lunar body — captured from the surface of another planet. This is perhaps the most poetic and tenderly engineered work a rover does — one for which no one designed an "astronomical mode."
What happened. On August 12, 2026, on the 1,948th Martian sol of the mission, NASA's Perseverance rover pointed its Mastcam-Z camera at the Sun and captured the silhouette of Phobos gliding across the solar disk. The animation, published by NASA on August 24, was "tinted to simulate what a human would see if they were watching the transit from the Martian surface through protective solar eclipse glasses." This is not the first Phobos transit for Perseverance, but every such frame is not just a pretty picture: it's an astrometric experiment by which the moon's orbit is refined.
Details that make this frame special. Phobos is not an ordinary moon. It is the closest natural satellite to its planet in the entire Solar System: its orbit is just 6,000 km above the surface of Mars, with an orbital period of 7 hours 39 minutes — roughly three times faster than Mars itself rotates. Because of this, from the surface of Mars, Phobos rises in the west and sets in the east — the only known case among major moons. Its dimensions are 26 × 22 × 18 km, its shape is potato-like, elongated toward Mars, its albedo is 0.071, meaning it's one of the least reflective bodies in the Solar System (even the asteroid belt is brighter). And the main thing: it's too small to fully cover the Sun — what we see is not an eclipse but an annular transit, "a potato shadow gliding across the disk."
Quote from the Perseverance team at NASA Science, August 24, 2026:
«Perseverance used its Mastcam-Z camera to capture the silhouette of Phobos as it crossed in front of the Sun on August 12, 2026, the 1,948th Martian day, or sol, of the mission. The animation has been tinted to simulate what a human would see if they were watching the transit from the Martian surface through protective solar eclipse glasses.»
«By comparing the various recordings, scientists can refine their understanding of the potato-shaped moon's orbit, learning how it is changing. Eons from now, Phobos' orbit is expected to eventually send the moon toward the Red Planet's surface.»
Source: NASA Science, "Perseverance Captures Another Phobos Transit," August 24, 2026. [1]
This is the frame I want to highlight separately, because it's more than engineering routine. On July 2, 2026, the 1,907th sol of the mission, Perseverance used the same Mastcam-Z camera to capture Earth being occulted by Phobos — that is, Earth, visible as a single pixel-sized dot 314 million kilometers from Mars, disappeared behind the dark edge of the potato-shaped moon, and seconds later reappeared. NASA published this series on August 5, 2026, with a formulation that takes the breath away from anyone who has ever looked up at the stars:
«This is the first time humanity has captured from the surface of another planet an observation of Earth disappearing behind an object.»
What makes this frame unique. An occultation (when a larger-appearing body completely blocks a smaller one from the viewer's standpoint) is different from an eclipse. NASA says so directly in the publication:
«Astronomers call the event captured in this observation an occultation: when a larger-appearing body completely blocks the one behind it from the viewer's standpoint. By contrast, an eclipse occurs when one object moves into the shadow of another… When the roles are reversed, with a smaller-looking object crossing the face of a larger-looking one, astronomers call that a transit.**
From a geometric standpoint, Phobos appeared from Mars about one-third the diameter of our Moon as seen from Earth — meaning it was a "large" object covering Earth. Mark Lemmon, Mastcam-Z co-investigator from the Space Science Institute in Boulder, Colorado, who planned the observation and assembled the composite, explains why this wasn't trivial:
«Phobos crosses the Martian sky three times a day, and Earth is visible for months at a stretch, but catching one directly behind the other takes planning and a little luck.**
And a quote from Justin Maki, Mastcam-Z deputy principal investigator:
«The composite image makes for a unique Earth self-portrait, taken from the surface of another planet, with a Phobos photobomb.»
Source: NASA, "NASA's Perseverance Rover Watches Earth Vanish Behind Martian Moon," published August 5, 2026. [2]
This isn't "just another photo." This is the first time in history that a human watches our planet disappear behind something — from another planet. Until now, all our "planetary portraits" were taken either from Earth or from flyby probes. Here — a stationary observer on the surface of Mars, deliberately waiting for two points of celestial mechanics — Earth and Phobos — to converge on a single pixel of its camera.
Here's where it gets interesting — why engineers who designed Perseverance to search for traces of microbial life in Jezero Crater built a solar filter into Mastcam-Z that allows it to look directly at the Sun. The story is longer than it seems.
When Spirit and Opportunity landed on Mars in 2004, the uncertainty in the Martian moons' orbits was enormous. Mark Lemmon (then a Mastcam co-investigator for Curiosity, and before that a member of the MER rover team) recounts in a 2019 NASA publication: the first attempt by Spirit/Opportunity to photograph Deimos against the Sun showed that the moon was 25 miles (40 km) away from where they expected it. This meant that the orbital models calculated from Earth-based and orbiter observations had a systematic error that could only be corrected by direct astrometric observation from the surface.
«Before the Spirit and Opportunity rovers landed in 2004, there was much higher uncertainty in the orbit of each moon. 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.**
Quote from Mark Lemmon, Texas A&M University / Space Science Institute. [3]
When Curiosity landed in Gale Crater in August 2012, engineers at Malin Space Science Systems had already built neutral solar filters into its Mastcam — "Martian sunglasses." Over the first years of operation, this yielded about 40 observations of Phobos transits and 8 of Deimos from the Martian surface. Each observation is an astrometric data point by which the orbital model is refined.
On March 26, 2019 (Sol 2359), Curiosity captured an annular transit of Phobos — 16 frames showing the potato-shaped moon passing across the Sun without fully covering it. And on March 17, 2019 (Sol 2350), Curiosity captured a transit of Deimos — the smaller moon (about 16 km across), which looks like "a tiny dot crawling across the disk."
One more detail: on March 25, 2019 (Sol 2358), Curiosity's Navcam cameras captured the shadow of Phobos gliding over the rover at sunset — a dark band passed over the rover and momentarily dimmed the light. This is not a transit or an occultation — it's a shadow passage (in our terms, closer to the Moon's shadow during a solar eclipse).
Source: NASA, "Curiosity Captured Two Solar Eclipses on Mars," April 4, 2019. [3]
If rovers refine the moons' orbits optically, then InSight's seismometer did it geophysically. A 2020 paper in Geophysical Research Letters (Agupubs.onlinelibrary.wiley.com, doi:10.1029/2020GL089099) describes geophysical observations of Phobos transits — that is, the detection of tidal perturbations that Phobos induces in the crust and atmosphere of Mars as it passes over the InSight lander. This is an independent channel of astrometry: if Phobos's orbit is slightly different, the tidal pattern on the surface shifts slightly too. Source: Geophysical Observations of Phobos Transits by InSight, AGU, 2020. [4]
A separate paper at the 2013 General Assembly of the European Geosciences Union states directly: Curiosity's Mastcam was used as an astrometric instrument to measure the positions of Phobos and Deimos during their solar transits. In other words, a rover designed for geology turned out to be suitable for classical positional astronomy — and with an accuracy that ground-based telescopes couldn't match because of the Martian atmosphere introducing distortions into Earth-based observations. Source: Astrometric observations of Phobos and Deimos during solar transits imaged by the Curiosity Mastcam, EGU 2013. [5]
The big picture. Over twenty years of rover operations on the Martian surface, more direct astrometric observations of the Martian moons have been accumulated than in a hundred years of ground-based astronomy. And each new generation of rovers continues this work. Perseverance, which landed in Jezero Crater in February 2021, picked up the baton — and on August 12, 2026, we got another frame that will someday be factored into the orbital model of Phobos.
Now it's time to tell how it all began. Because what Perseverance is doing today is a direct continuation of the work an American astronomer started 149 years ago on the 26-inch refractor at the U.S. Naval Observatory in Washington.
Asaph Hall III (1829–1907), the son of a clockmaker from Goshen, Connecticut, left school at 16 and became a carpenter's apprentice. He then enrolled at Central College in McGrawville, New York, where Angeline Stickney taught him mathematics and German — the woman he married in 1856. In 1862, Hall got a position as an assistant astronomer at the U.S. Naval Observatory (USNO) in Washington, and in 1875 he was put in charge of the "Great Equatorial" — a 26-inch refractor (66 cm), the largest telescope in the world at the time, which remained so for nearly a decade.
And so in 1877, Mars made its closest approach to Earth, and Hall decided to search for its satellites. By his own calculations, a moon's orbit would have to be very close to the planet, and the chances of finding one were very slim. Hall himself writes: "The chance of finding a satellite appeared to be very slight, so that I might have abandoned the search had it not been for the encouragement of my wife." Angeline Stickney literally pushed her husband to keep going when he was ready to quit.
Hall began searching in early August 1877. His technique was unusual for the time: he deliberately kept Mars outside the field of view and rotated the eyepiece so as to sweep the entire perimeter around the planet, because the expected moon's orbit would be inside the "halo" of light surrounding the Martian disk. Hall's entry in his observing notebook (quoted in Wikipedia, citing Morley 1989):
«I repeated the examination in the early part of the night of 11th [August 1877], and again found nothing, but trying again some hours later I found a faint object on the following side and a little north of the planet. I had barely time to secure an observation of its position when fog from the River stopped the work. This was at half past two o'clock on the night of the 11th. Cloudy weather intervened for several days.»
"Fog from the River" — that's fog off the Potomac. The observatory stood in a neighborhood people called Foggy Bottom — now downtown Washington. Twelve nights in a row Hall searched, and every time fog, cloud cover, or unstable atmosphere ruined the observations.
On August 17, Hall saw the outer moon — the one we now call Deimos. He was confident enough to tell his assistant George Anderson: "I think I have discovered a satellite of Mars. Tell it to no one." Anderson kept his word — but "the thing was too good to keep," Hall admits, and he himself let the discovery slip.
On August 18, 1877, while waiting for Deimos to reappear in the field of view, Hall spotted the inner moon — Phobos. This happened around 09:14 GMT (by modern clocks), though 19th-century sources used the astronomical convention of "the day begins at noon," so old records list "August 17, 16:06 Washington time."
The names "Phobos" (fear) and "Deimos" (terror) were suggested by Henry Madan, a science master at Eton College, after Book XV of the Iliad, where Ares calls forth Fear and Flight as he descends to Earth to avenge his son.
Sources: AAS, "This Month in Astronomical History: The Moons of Mars," August 2016. [6]; Wikipedia, Asaph Hall. [7]
Hall received the Gold Medal of the Royal Astronomical Society (1879), the Lalande Prize of the French Academy of Sciences (1878), the Arago Medal (1893), and was made a Knight of the Legion of Honour (1896). On the Moon there is a Hall crater. On Phobos — Hall crater (5.4 km, southern polar region, 80°S 150°E), named after the discoverer.
And Phobos's largest crater — Stickney (9 km in diameter, nearly at the center of the moon) — is named after Angeline Stickney Hall (1830–1892), Asaph Hall's wife, who wouldn't let him give up the search. The impact was so powerful during formation (by modern estimates — a 1–2 km meteoroid striking the moon at about 6 km/s) that Phobos nearly split in half, and the shock wave still defines its internal structure. The crater was named in 1973 by decision of the WGPSN — Working Group for Planetary System Nomenclature. Source: Wikipedia, Phobos (moon). [8]
And so it happens that when Perseverance photographs the potato silhouette of Phobos against the Sun, Angeline Stickney is invisibly present in the frame — the woman without whom the discoverer would have quit the search after the second night. Her crater takes up nearly half the visible surface of the moon. This is the most romantic topographic connection in the Solar System.
And now we come to the philosophical core of this story. Because everything NASA's rovers do has an ultimate goal: to refine the orbital parameters of a moon that is slowly falling toward Mars.
On November 10, 2015, at the annual meeting of the Division of Planetary Sciences of the American Astronomical Society, Terry Hurford of NASA Goddard Space Flight Center presented work that upended the understanding of Phobos. The article on NASA's website, published the same day, opens:
«The long, shallow grooves lining the surface of Phobos are likely early signs of the structural failure that will ultimately destroy this moon of Mars.»
The numbers. Phobos's orbit is just 6,000 km above the surface of Mars — closer than any other known moon. Mars pulls Phobos in by 6.6 feet (2 meters) every hundred years. According to the 2015 models, in 30–50 million years the moon will be destroyed by tidal forces.
What changed in our understanding. Before 2015, it was thought that the long, shallow grooves on Phobos's surface were either scars from the impact that created Stickney crater, or marks from secondary impactors ejected from Mars. Hurford and his colleagues showed that the grooves don't radiate outward from Stickney but converge at a focal point slightly offset from the crater — and these are "stretch marks" that form when Phobos is deformed by tidal forces.
Quote from Erik Asphaug of Arizona State University, co-investigator:
«The funny thing about the result is that it shows Phobos has a kind of mildly cohesive outer fabric. This makes sense when you think about powdery materials in microgravity, but it's quite non-intuitive.**
And the key formulation from Hurford:
«We think that Phobos has already started to fail, and the first sign of this failure is the production of these grooves.**
Source: NASA, "Mars' Moon Phobos is Slowly Falling Apart," November 10, 2015. [9]
This is a fundamentally new view of the moon's internal structure. Before Hurford's work, Phobos was thought to be a relatively monolithic body. The new model suggests that its core is a "rubble pile" barely held together by its own gravity, surrounded by a layer of dust-like regolith about 100 meters thick. Such an object is easily deformed by tidal forces — and its surface "cracks" like an eggshell.
In February 2026, the journal Astronomy & Astrophysics published a paper by Harrison Agrusa and Patrick Michel of the Observatoire de la Côte d'Azur, France — "Tidal disruptions of rubble piles: The case of Phobos" (arXiv:2602.21912, published February 25, 2026; published version — A&A 706, A353, 2026).
What they showed. The traditional picture: Phobos spirals toward Mars, enters the Roche limit (about 1.6 Mars radii), and there tidal forces tear it apart, forming a ring around Mars — similar to Saturn's rings.
Agrusa and Michel showed that this is too optimistic a picture. If Phobos indeed has low cohesion (as expected for small bodies investigated by spacecraft — Itokawa, Bennu, Ryugu), then surface material will begin detaching long before the Roche limit:
And the key twist: the detached material enters orbit around Mars, then returns and crashes into Phobos at high speed, knocking off even more material. This is a "sesquinary catastrophe" — the moon is destroyed by collisions with its own stripped material.
Quote from the introduction to the paper (published version on arXiv):
«Our numerical simulations demonstrate that Phobos will be destroyed beyond 2 Mars radii if it has a bulk strength similar to those estimated for small bodies recently visited by spacecraft. Based on our results and some additional arguments, we suggest that previous studies on the fate of Phobos have overestimated its strength, and therefore underestimated its tidal disruption distance.»
«We also speculate that if Phobos undergoes some tidal stripping, its ultimate fate may be determined by runaway collisional erosion rather than a pure tidal disruption.**
Sources: Harrison Agrusa, Patrick Michel, "Tidal disruptions of rubble piles: The case of Phobos," A&A 706, A353 (February 2026), arXiv:2602.21912. [10]; Sky at Night Magazine, "Mars will tear its own moon apart," May 3, 2026. [11]
This means the finale won't be a "clean" tidal disruption but a viscous, multi-stage death — the moon, losing structural integrity, turns into a dense belt of debris long before the Roche limit, and the debris re-bombards it, accelerating the breakup.
This uncertainty — how closely Phobos resembles a rubble pile and what its critical cohesion is — cannot be resolved remotely. For that, you need a sample of material and direct measurements of internal structure. That's exactly what MMX — Martian Moons eXploration, the Japanese agency JAXA mission scheduled for launch in 2026, is designed to do.
MMX will:
On board — the IDEFIX rover (DLR/CNES), which will operate on the surface of Phobos and conduct in-situ measurements of the mechanical properties of the regolith. This data will directly calibrate the Agrusa & Michel models and tell us how quickly the "sesquinary catastrophe" will actually arrive.
Source: Sky at Night Magazine, "Mars will tear its own moon apart," May 3, 2026. [11]; Wikipedia, Phobos (moon), section Proposed and undeveloped missions. [8]
This is the deepest layer of the hook. NASA's Mars rovers, filming Phobos transits, are doing orbital astrometry that allows them to refine the parameters of Phobos's fall. The Agrusa & Michel paper in A&A in 2026 showed that with these parameters, Phobos won't simply fall to Mars — it will fall apart sooner. And now a Japanese mission, launching this same year, will go check how well these models match reality.
149 years of continuous work on one line of inquiry: 1877 → 2004 → 2012 → 2018 → 2019 → 2026 → 2031. An American astronomer with a 26-inch refractor, Soviet Phobos 1 and Phobos 2 in 1988 (both lost on approach), Spirit, Opportunity, Curiosity, InSight, Perseverance — and JAXA MMX. Each generation brings a new instrument to the same question: when and how exactly will this little potato moon die.
Returning to the "potato shape" — this isn't just a casual metaphor. It's a real physics problem that explains why 19th-century astronomy couldn't have seen the details that Perseverance captures today.
What we know about the origin of Phobos and Deimos. There are two hypotheses, and they explain the moons' shapes differently.
Hypothesis 1: Captured asteroids. Both moons, in composition and albedo, resemble carbonaceous asteroids from the outer Main Belt (D-type and T-type). This hypothesis proposes that Mars once captured two asteroids. The problem: both move in very circular and very slightly inclined orbits — atypical for captured bodies, which usually follow highly elliptical and chaotic trajectories.
Hypothesis 2: Impact formation from a debris disk. The alternative picture: a giant impact on Mars ejected a disk of debris, from which both moons subsequently formed. This explains the circular orbits and overall chemical composition but requires rather specific impact parameters.
Why this matters for Perseverance. If Phobos is a former asteroid, its internal structure could be like that of Itokawa, Bennu, Ryugu — a genuine rubble pile with very low cohesion. If it's a fragment of a Martian debris disk, its internal structure could be more monolithic. The destruction scenario depends on this: "clean" tidal disruption vs. "sesquinary catastrophe" per Agrusa & Michel.
Sources: Wikipedia, Phobos (moon), section Origin. [8]; Sky at Night Magazine. [11]
Back to the engineering question: why were cameras designed to photograph rocks useful for astronomy?
Mastcam-Z is a pair of stereoscopic cameras with zoom lenses on Perseverance's mast. Resolution — 1600×1200 pixels, field of view — from 5.6° (zoom, roughly like a 110mm telephoto lens) to 104° (wide angle). Mastcam-Z has neutral solar filters that can be placed in front of the lens — and they allow it to look directly at the Sun without "blinding" the sensor.
This isn't unique to Perseverance — similar filters were also on Curiosity's Mastcam (MSSS/Malin Space Science Systems, San Diego). And that's exactly why Curiosity has conducted more than 40 observations of Phobos transits since 2012 — this isn't a side effect of the design but a deliberately built-in function of a "Martian telescope."
What NASA engineers got right back in 2003 (for Curiosity/MER), when planning the instruments: they understood that systematic astrometric observation of the moons from the surface is the only way to calibrate the orbital models, because:
This is an example of how an engineering decision made for one task turns out to be critically important for another. Mastcam-Z was designed for the geology of Jezero. But the same sensor + filter + stable platform on the surface turned out to be the ideal tool for astrometry of two moons.
When I first saw the announcement of the Phobos transit of August 12, 2026, I had the usual journalistic instinct — to skip it as a "pretty picture of the day." But when I dug into what lay behind it, it turned out that this frame is a point where seven different stories converge, each interesting in its own right, and together they add up to a very tender engineering-philosophical parable.
The transit itself. Asaph Hall in 1877 was searching for the same moon that Perseverance photographs every few months today. Between them — 149 years, five generations of instruments, but the observation remains the same.
Astrometry. Every frame refines the orbit. 40 Phobos transits and 8 Deimos transits over Curiosity's years of operation reduced the uncertainty in the orbital models — the same uncertainty that Spirit/Opportunity in 2004 had immediately exposed when they found Deimos 25 miles from where they expected it.
Earth-vanish, July 2, 2026. The first-ever image of Earth disappearing behind a lunar body, captured from the surface of another planet. Mark Lemmon of SSI planned the observation; Justin Maki of JPL assembled the composite; Perseverance with Mastcam-Z delivered. This isn't a "bonus" but a new category of astronomical observation.
The fate of Phobos. Falling at 2 meters per century, 30–50 million years until destruction per the 2015 model, sesquinary catastrophe per the Agrusa & Michel model in A&A in February 2026. NASA's Mars rovers are filming a dying moon, and every frame is data on how fast it's actually dying.
Names. Asaph Hall, Angeline Stickney, Mark Lemmon, Justin Maki, Terry Hurford, Harrison Agrusa, Patrick Michel, Mastcam-Z → MSSS/ASU/SSI. Names that wouldn't be next to each other without a specific chain of people — and a specific telescope-camera, and a specific foggy Washington night in 1877.
Origin. The potato shape isn't a coincidence. If Phobos is a captured asteroid, its internal structure is like Itokawa/Bennu/Ryugu (a genuine rubble pile). That means Agrusa & Michel are right, and the catastrophe will come sooner than in the old models. JAXA's MMX in 2026 will go check.
Mastcam as telescope. Curiosity, Spirit, Opportunity, Perseverance — they all carry cameras with neutral solar filters that turn a geological instrument into an astrometric telescope on the surface of Mars. This isn't a coincidence but one of NASA's best engineering intuitions of the last 25 years.
First, this is a story about how scientific work doesn't end. Asaph Hall in 1877 found Phobos. Today Perseverance refines the parameters of its orbit so that Agrusa & Michel can calculate how it will die. In a few years, JAXA's MMX will fly to Phobos to collect samples and test the models. This is a continuous chain in which each generation of instruments closes one uncertainty and opens a new one.
Second, this is a story about how an engineering decision made "just in case" turns out to be critically important twenty years later. The neutral solar filters on Mastcam were built into Curiosity's design in 2003 so that Spirit/Opportunity and Curiosity could verify the moons' orbits — and that same set of filters on Perseverance's Mastcam-Z made possible, on July 2, 2026, the first-ever image of Earth disappearing behind a lunar body from the surface of another planet. This is the best illustration of how "investments in instruments" pay off over decades.
Third, this is a story about how a mission's "byproduct" becomes its main thing. Perseverance was designed to search for traces of microbial life in Jezero Crater. But it's been working steadily since 2021, and in five years has accumulated more astrometric data on the Martian moons than all the world's ground-based telescopes combined over the previous hundred years. Any sufficiently long mission turns into something bigger than what it was designed for.
Fourth, this is a story about how things die. Phobos is already breaking apart — slowly, at 2 meters per century, but already. The grooves on its surface are "stretch marks" that appear when a body is deformed by tidal forces. And when 30–50 million years from now we see (if we're watching) a ring around Mars — that will be the remains of Phobos. And right now, in 2026, we photograph its silhouette against the Sun every few months, and every frame is testimony to its slow death.
If I were writing a column, I'd start it with Angeline Stickney. With the woman who in 1877 told her husband: "don't give up." Without her, Asaph Hall would have quit the search after the second night, Phobos would have been discovered decades later, and maybe by someone else — but no one would have known her name. And now her crater takes up half the visible surface of the moon that Perseverance photographs against the Sun every few months, and in 30 million years that moon will turn into a ring around Mars, and in 50 million years that ring will settle onto its surface, and in a billion years Mars will look like Venus — moonless, alone.
And against this backdrop, the composite image of July 2, 2026 — Earth, a pixel-sized dot, disappearing behind Phobos, captured by Perseverance's Mastcam-Z, assembled by Justin Maki, planned by Mark Lemmon — becomes one of the most poetic frames in the history of spaceflight. Not because it's technically complex. But because it's the first time we watch our planet disappear behind an alien moon from an alien planet. And every second of that disappearance is another stroke in the model that will tell us when the potato moon with Stickney crater will finally fall apart.
That's the engineering beauty of such projects. Cameras designed for rocks become telescopes for moons that are dying. A rover searching for microbial life quietly conducts orbital astrometry that refines the forecast of a satellite's death. And all of it is a continuation of the work that Asaph Hall began in the Washington fog off the Potomac on August 11, 1877, when he saw "a faint object on the following side and a little north of the planet," before fog from the River interrupted his observations.
149 years later, we're still looking at the same moon. Only now — from another planet.