After almost two decades of continuous observation of the Red Planet, NASA's spacecraft Mars Reconnaissance Orbiter (MRO) and its key camera HiRISE have reached a historic threshold: the one hundred thousandth high-resolution image of the surface of Mars has been captured and processed. The million pixels of the latest recording, captured on October 7, 2025, reveal a dramatic landscape of plateaus and sand dunes in the Syrtis Major region, only about 80 kilometers southeast of the Jezero crater where the rover Perseverance is exploring. Behind that single image lies a story of a long-lived orbiter mission, technological engineering, and the way Mars is becoming increasingly familiar – not only to scientists but also to the wider public.

HiRISE, short for High Resolution Imaging Science Experiment, is the most powerful camera ever sent into orbit around another planet. Placed on the MRO since the spacecraft entered its science orbit in 2006, this half-meter telescopic camera can, in favorable conditions, resolve details ranging in size from about 30 to 50 centimeters on the surface of Mars. Such a level of detail has allowed rover tracks, parachutes, and craters from their landings to be clearly spotted, but also much subtler geological structures – ice deposits, thin layers of dust, cracked channels, and dynamic dune shapes.

The latest image of Syrtis Major is exactly such a mosaic of subtle nuances. On it, mesas – flat-topped elevations with nearly vertical steep slopes – and dark bands of dunes that stretch like rivers of sand through valleys and lowlands stand out clearly. Differences in color, emphasized by the special "enhanced" view of HiRISE, reveal changes in mineral composition and material granulation. Scientific teams are analyzing how the wind behaves in that region, from which directions it brings sand, and in what way that material gets caught in natural "traps" of the terrain, building dunes that slowly migrate over the years.

The Syrtis Major region is one of the historically most famous dark markings on Mars, visible even through telescopes of the 17th century. Today, in the era of orbiters and rovers, it is scientifically even more intriguing. It is located on the border between ancient volcanic plates and lighter, dustier lowlands, and its dunes and layered sediments preserve records of climate changes, wind directions, and the eventual presence of ice closer to the surface. The fact that the one hundred thousandth HiRISE image focuses on precisely that piece of terrain, distant only about 85 kilometers from the location of the rover Perseverance in the Jezero crater, symbolically connects the orbiter and rover in a unique research mosaic.

Mars Reconnaissance Orbiter was launched on August 12, 2005, from Cape Canaveral, and entered orbit around Mars on March 10, 2006. After the aerobraking phase, during which the spacecraft gradually slowed down by passing through the upper layers of the Martian atmosphere, MRO began its primary science mission in November 2006. Although it was originally planned that the mission would last only a few years, the spacecraft still operates stably today, already in its sixth extended mission, and has become the second longest-lived orbiter around Mars, right behind the Mars Odyssey mission.

During almost twenty years of operation, MRO has, according to official data, transmitted more than 450 terabits of scientific data to Earth, of which a large part consists precisely of HiRISE recordings. These images are not just impressive "postcards" of Mars. They are the foundation for detailed surface mapping, selection of future landing sites, discovery of fresh craters in which pure water ice has been ejected, as well as for monitoring seasonal changes – from thin accumulations of frost to dust clouds that cover entire regions.

The HiRISE camera is by construction a powerful reflecting telescope with a primary mirror diameter of 0.5 meters. At the focal point sits an array of CCD detectors that record in three spectral bands: red, blue-green, and near-infrared. At full width, the red channel produces images about 6 kilometers wide with a horizontal resolution of over 20 thousand pixels, while the side color channels cover narrower areas but allow for the reconstruction of false colors that emphasize differences in the composition of rocks and sand. In practice, this means that a single HiRISE scene, like the latest image of Syrtis Major, can occupy hundreds of megabytes of raw data.

The one hundred thousandth recording arrived at a moment when the camera itself bears traces of aging. Back in 2023, part of the electronics connected to one of the CCD assemblies (the so-called RED4) stopped working, which in the final products leaves a characteristic dark "gap" in the middle of the image and reduces the width of the area covered in color. Engineers and scientists from the HiRISE team in Arizona emphasize that this does not affect the main scientific value of the recordings: the same spatial resolutions are still obtained, and a large part of the frame is still available in full, enhanced color. In parallel, possibilities for partial recovery of the problematic channel or additional software correction of artifacts are being explored.

Despite technical challenges, HiRISE is still the key "eye" of NASA's Martian flotilla. Precisely its recordings, together with the somewhat wider but lower resolution context camera CTX and the wide-angle instrument MARCI, were crucial in selecting safe and scientifically interesting locations for the Phoenix, Curiosity, InSight, and Perseverance missions. Before every landing, the orbiter detailedly inspects potential areas, looking for slopes, rock blocks, and dunes that could pose a risk to landers and rovers. HiRISE also monitored spectacular moments of entry, descent, and landing – among others, it recorded the scene of the rover Curiosity hanging beneath its parachute over Gale Crater and later the same scene for Perseverance above Jezero.

HiRISE is at the same time an instrument that has changed our view of the dynamics of the Martian surface. Long-term monitoring of the same locations has shown that dunes literally "march" under the influence of the wind, sometimes even by several meters per year. Avalanches of ice and dust on the steep slopes of polar caps, rockfalls on cliffs, and the sudden appearance of dark streaks and spots connected to the seasonal evaporation of frozen carbon dioxide have also been recorded. All these phenomena indicate that Mars, although cold and dry today, is not a static world but a planet that is still changing.

The latest image of Syrtis Major fits into that story of a changing landscape. The dunes there form as a consequence of the long-term action of the wind which pulverizes rocks, transports sand, and deposits it in the lees behind elevations. Mesas and crater rims serve as natural obstacles, creating zones where vortices slow down and release a load of sand. By analyzing the thickness, shape, and arrangement of dunes, scientists try to reconstruct how wind directions have changed over the years, and even decades, and how much these changes are connected to global seasonal cycles on Mars.

It is particularly interesting that precisely this location for imaging was proposed by a high school student via the platform HiWish. This is a public system for suggesting imaging targets that allows everyone interested, from scientists to students, to propose specific locations on Mars that HiRISE should record. The expert team then verifies the scientific value and technical feasibility of the proposal, and selected targets enter the list of planned observations. In the case of the one hundred thousandth image, the decision to grant the student's proposal nicely shows how much the space around Mars has become an educational, and not just a scientific arena.

The democratization of data is another important aspect of the HiRISE program. Recordings are published very quickly after reception and basic processing, in publicly available catalogs where anyone can browse, download, and analyze data. Researchers around the world use these images to create their own maps, 3D models, and numerical simulations, while artists and science popularizers create impressive visualizations and educational materials from the same data. The University of Arizona additionally develops digital terrain models (DTM) from pairs of HiRISE recordings, so Mars can be "flown over" through virtual videos almost as if it were recorded by a drone.

MRO therein does not serve only as a photographic platform. The spacecraft is a key communications bridge between rovers on the ground and deep space antennas on Earth. Through its system of antennas and transmitters pass enormous amounts of data sent by Perseverance and Curiosity, and MRO simultaneously collects its own recordings and measurements. NASA estimates that the orbiter has enough fuel and resources to continue working at least until the mid-2030s, which means that HiRISE will remain one of the main sources of information about the surface of Mars in the next decade as well.

The one hundred thousandth image is therefore not just a statistical figure, but also a reminder of how much our knowledge of Mars has expanded thanks to one orbiter and one camera. When MRO was launched, the Spirit and Opportunity missions were just ending on the surface, and Curiosity and Perseverance existed only on blueprints. Today HiRISE records traces of multiple generations of rovers, tracking their movements and recording changes they cause on the ground. In combination with other instruments on MRO, and with a fleet of European and Indian orbiters, a detailed chronicle of climatic and geological processes has been obtained that exceeds initial expectations.

Even the HiRISE team itself does not view its images only as scientific data, but also as an opportunity to bring Mars closer to the wider public. Through projects like BeautifulMars e-books and podcasts, and through constant presence on social networks, they choose visually striking scenes – like voluminous dunes, layered rocks, or channels filled with fog – and turn them into stories about the origin and development of Mars. The latest endeavor also includes recording a rare interstellar visitor, the comet 3I/ATLAS, when MRO temporarily turned its camera from Mars toward darker parts of the sky.

At the moment when images and videos related to the one hundred thousandth HiRISE recording are being published on NASA's pages, it is clear that this milestone is not an end, but a new point on a growing curve of data. Every new orbit around Mars is an opportunity to capture yet another window into the past and present of the Red Planet. Syrtis Major, with a combination of mesas, dunes, and rocky plateaus, is in that sense an ideal symbol of what HiRISE does best: it combines the pure aesthetics of space photography with precise scientific analysis, leaving behind an archive of images that will be studied for decades to come.