Could the secrets of another star system be hidden in a faint smudge captured from Mars? In early October, NASA achieved a rare observational milestone: three of its Mars-based assets, MRO, MAVEN, and the Perseverance rover, turned their instruments toward 3I/ATLAS, only the third confirmed interstellar object to traverse our solar system. Its passage within 30 million kilometers of Mars offered the closest vantage point any NASA spacecraft is expected to obtain, enabling scrutiny impossible from Earth-based telescopes during its Sun-concealed trajectory.
MRO’s HiRISE camera is capable of resolving Martian surface features down to 24 centimeters per pixel and was repurposed for deep-space imaging by rotating the spacecraft to track the comet. The technique, used once before during the 2014 flyby of comet Siding Spring, required precise targeting to avoid contamination from Mars’ thin atmosphere and stray sunlight. The resulting images, with a resolution of about 30 kilometers per pixel, show the coma-the diffuse cloud of dust and ice surrounding the nucleus-measuring about 1,500 kilometers across. “Observations of interstellar objects are still rare enough that we learn something new on every occasion,” according to Shane Byrne, HiRISE principal investigator. Scientists hope to glean information regarding particle size distribution, color, and perhaps detect sunward jets within the coma that can lead to knowledge about sublimation dynamics as the comet approaches perihelion.
Complementary insights were provided by MAVEN’s IUVS, which captured multi-wavelength UV imagery over a ten-day campaign. This approach isolates emissions from key species such as hydrogen, hydroxyl, carbon, and oxygen, enabling chemical fingerprinting of the comet’s volatile inventory. By mapping hydrogen release, MAVEN scientists derived an upper limit for the deuterium-to-hydrogen (D/H) ratio, a critical tracer for determining the comet’s formation environment. As noted in prior cometary studies, D/H ratios vary between solar system reservoirs, offering clues to whether an object formed in the cold outer reaches of its native system or closer to its star. Shannon Curry, MAVEN’s principal investigator, described the data as “incredible,” underscoring that the team has “only scraped the surface” of the analysis.
Perseverance’s Mastcam-Z added a unique perspective from the Martian surface despite substantial technical hurdles. Fixed in place during the long exposures, the camera produced star trails while barely registering the comet as a dim point-a consequence of attempting to track so faint and fast a target without a gimbal system. This approach parallels other planetary missions when attempting to image transient astronomical phenomena from static platforms.
The technical achievement does not only lie in the instruments’ sensitivity but is also reflected in the coordinated timing across the platforms. HiRISE’s optical data, the spectrographic measurements of MAVEN, and Mastcam-Z imagery at the surface level form a multiscale data set, bridging visible and ultraviolet regimes. This integration mirrors similar methodologies utilized in previous comet encounters, where remote sensing and in situ measurements combined to characterize dust morphology, volatile composition, and particle kinematics.
Most importantly, the detection and confirmation of interstellar objects like 3I/ATLAS depend on intensive astrometric follow-up to distinguish hyperbolic trajectories from bound cometary orbits. The ATLAS survey telescope in Chile first detected the object in July of this year, with follow-up from Hubble, James Webb, and other observatories. However, Mars-based observations during its solar conjunction filled a critical gap, as Earth-based instruments were shielded by proximity to the Sun. This approach parallels campaigns associated with heliophysics missions, in which spacecraft such as STEREO and SOHO leverage unique viewing geometries to monitor comets inaccessible from Earth.
The scientific payoff extends beyond compositional data. Interstellar comets are considered to be ejected planetesimals from other star systems, their velocities and isotopic signatures sculpted by the dynamics of stellar flybys, planetary scattering, or late-stage stellar evolution. Modeling suggests that ejection velocities from planetary scattering can reach several kilometers per second, while flyby-induced ejections tend to be slower, in the 0.5–2 km/s range. Measuring current motion and rotation rates possible through comparative imaging before and after perihelion may help constrain 3I/ATLAS’s origin scenario.
For planetary scientists and astronomers, the conjunction of engineering precision with astrophysical opportunity in this campaign represents a rare alignment. Every photon captured from 3I/ATLAS carries information from a distant stellar nursery, now decoded through the combined capabilities of orbiters and a rover stationed on another world.
