NASA’s Mars Spacecraft Capture Close-Up Views of Comet 3I/ATLAS

In early October 2025, NASA’s Mars missions had a rare front-row seat to a visitor from beyond our solar system: the interstellar comet 3I/ATLAS. Three separate spacecraft — the Mars Reconnaissance Orbiter (MRO), the MAVEN orbiter, and the Perseverance rover — all turned their instruments toward this object, providing new insights into its nature.

A Unique Observation Opportunity

At its closest approach, 3I/ATLAS passed roughly 19 million miles (30 million km) from MRO, giving us one of the clearest perspectives of this comet from any spacecraft.

MRO / HiRISE: The High-Resolution Imaging Science Experiment (HiRISE) camera aboard MRO captured the comet on October 2, 2025.

While HiRISE typically images Mars itself, mission controllers repointed it toward space — a maneuver used before, notably during the Siding Spring comet flyby.
NASA Jet Propulsion Laboratory (JPL)

At the distance of observation, the comet’s image appears as a roughly 19 miles (30 km) per pixel dot, representing the coma — the surrounding cloud of dust and ice that the comet sheds as it warms.

Studying the HiRISE data could help scientists estimate the size of the comet’s nucleus (its solid core) and characterize the particles in its coma.

Comet Chemistry from Ultraviolet Images

The MAVEN orbiter contributed a complementary view using its Imaging Ultraviolet Spectrograph (IUVS). Over a 10-day period starting around September 27, MAVEN collected UV images that revealed hydrogen emission from the comet — a critical indicator of water vapor being released.

By analyzing different wavelengths, the team can identify molecules in the coma, such as hydrogen and hydroxyl.

One key result is an estimate of the comet’s deuterium-to-hydrogen ratio, which provides clues about its origin and evolutionary history.

A Glimpse from the Surface of Mars

On October 4, Perseverance also caught a faint glimpse of 3I/ATLAS from the Martian surface, using its Mastcam-Z camera.

The exposure had to be unusually long to detect such a dim object, and because the camera is fixed, longer exposure leads to star trails in the background — making the comet appear as a faint smudge.
NASA Jet Propulsion Laboratory (JPL)

Even this faint image is scientifically valuable, adding to the multi-point observation campaign.

Why This Matters

Observing an interstellar comet from three different platforms around Mars is extraordinary, because:

Size and Structure: HiRISE data may help pin down the nucleus size and reveal the composition or color of particles in the coma.
NASA Jet Propulsion Laboratory (JPL)

Chemical Composition: MAVEN’s UV observations are critical for understanding the molecular composition of the comet and how much water it releases.

Interstellar Origins: Because 3I/ATLAS comes from outside our solar system, studying it offers a rare window into materials born in another star system.

As Shane Byrne, HiRISE’s principal investigator at the University of Arizona, put it:

“Observations of interstellar objects are still rare enough that we learn something new on every occasion … We’re fortunate that 3I/ATLAS passed this close to Mars.”

Leslie Tamppari, project scientist for MRO at JPL, added that this event highlights the flexibility of Mars missions:

“This is one of those occasions where we get to study a passing space object as well.”
NASA Jet Propulsion Laboratory (JPL)

What Comes Next

Scientists will continue analyzing the HiRISE and MAVEN datasets to refine estimates of the comet’s nucleus size, composition, and behavior.

The UV data from MAVEN, especially, may shed more light on how much water the comet is releasing and how its chemical signature compares to comets from our own solar system.