Mars Reconnaissance Orbiter Snaps Close-Ups of Interstellar Comet 3I/ATLAS
New images from the High Resolution Imaging Science Experiment camera on board NASA’s Mars Reconnaissance Orbiter will allow astronomers to better estimate the size of 3I/ATLAS, the third known interstellar object to pass through the solar system.
This 3I/ATLAS image was captured by the HiRISE camera aboard NASA’s Mars Reconnaissance Orbiter on October 2, 2025. Image credit: Image credit: NASA / JPL-Caltech / University of Arizona.
On October 2, 2025, the Mars Reconnaissance Orbiter (MRO) observed 3I/ATLAS from 30 million kilometers (19 million miles).
The orbiter team observed the comet with the High Resolution Imaging Science Experiment (HiRISE) instrument, which normally points toward the Martian surface.
By rotating, the spacecraft can also point its camera at celestial objects – a technique used in 2014, when HiRISE joined MAVEN to study another comet, Siding Spring.
“Observations of interstellar objects are still rare enough that we learn something new at every opportunity,” said HiRISE principal investigator Dr. Shane Byrne, a research scientist at the University of Arizona.
“We are lucky that 3I/ATLAS passed so close to Mars.”
Captured at a scale of about 30 km (19 miles) per pixel, 3I/ATLAS looks like a pixelated white ball in HiRISE images.
“This ball is a cloud of dust and ice called a coma, which the comet released as it continued its trajectory beyond Mars,” the researchers explained.
Further study of the HiRISE images could help scientists place an upper limit on the size of the comet’s nucleus, its central core made of ice and dust.
The images could also reveal the properties of particles in the atmosphere surrounding the comet, called coma.
Continued analysis of the images can even reveal core fragments or jets of gas, which are sometimes released when comets break up over time.
“One of MRO’s greatest contributions to NASA’s work on Mars has been the observation of surface phenomena that only HiRISE can see,” said MRO project scientist Dr. Leslie Tamppari, a research scientist at NASA’s Jet Propulsion Laboratory.
“This is one of those occasions where we can also study a passing space object.”
“Thanks to NASA’s fleet of capable spacecraft covering the inner solar system, we can continue to observe this dynamic object, and from unique angles,” said HiRISE co-investigator Professor James Wray, a researcher at the Georgia Institute of Technology.
“The three interstellar objects to date have shown striking differences from each other and from typical comets in the solar system, so every new observation we make is valuable.”
“Seeing a visitor from another star system is extraordinary in itself,” said Dr. Tomás Díaz de la Rubia, senior vice president for research and partnerships at the University of Arizona.
“Doing it from a University of Arizona-led instrument orbiting Mars makes this even more remarkable.”
“This moment is a testament to the ingenuity of our scientists and the lasting impact of this university’s leadership in space exploration.” »
“HiRISE exemplifies how discovery tools serve science and the public good. »
