Blind dates often bring an element of surprise and excitement, especially when the date involves an interstellar object of unknown origin. On October 3, 2025, the interstellar object known as 3I/ATLAS will make a close approach, passing within 29 million kilometers of Mars. This event presents a unique opportunity for scientists, as the HiRISE camera onboard the Mars Reconnaissance Orbiter will be capable of capturing images of 3I/ATLAS at an impressive resolution of 30 kilometers per pixel.
The images captured during this close encounter could provide valuable insights into the characteristics of 3I/ATLAS. Specifically, they may help distinguish between the contributions of the nucleus and the surrounding dust cloud to the total brightness observed from the object. Notably, the Minimum Orbit Intersection Distance (MOID) of 3I/ATLAS from Mars is a mere 2.7 million kilometers, indicating a remarkably precise trajectory that could suggest advanced technological origins.
If 3I/ATLAS is indeed a technological object, the short MOID could facilitate the arrival of a precursor mini-probe to Mars. A slight adjustment in orbit—by about 10–15 kilometers per second—in September 2025 could even reduce the closest approach distance of 3I/ATLAS to zero, as detailed in my collaborative research with Adam Hibberd and Adam Crowl. The findings are accessible here.
It is important to note that the ejection of icy fragments from the surface of a natural comet typically results in a velocity kick of approximately 0.4 kilometers per second, based on data from the Webb telescope. This speed is insufficient for these fragments to reach Mars. Additionally, the extent of the CO2 plume observed by SPHEREx around 3I/ATLAS is around 350,000 kilometers, which is still significantly shorter than the distance required for the plume to reach Mars without any maneuvering.
Considering these factors, the arrival of materials from 3I/ATLAS to Mars in October 2025 could potentially serve as a signature of advanced technology. Fortunately, the recent Labor Day holiday provided a brief respite from my administrative responsibilities as the director of Harvard’s Institute for Theory & Computation. During this time, I calculated that if 3I/ATLAS carries a precursor probe moving ahead and sideways towards Mars from approximately 30 million kilometers away, this probe could intercept Mars on or around October 3, 2025.
This scenario creates a compelling reason to utilize the HiRISE camera within the month leading up to the encounter. In addition to imaging the nucleus and dust cloud of 3I/ATLAS, HiRISE could also be deployed to search for any precursor objects that may approach Mars more closely than the main object itself. Notably, current near-Earth telescopes struggle to detect sunlight reflections from objects smaller than 100 meters, which is the upper limit for the size of all human-launched space probes to date.
In summary, the potential close encounter with 3I/ATLAS offers a thrilling opportunity for scientific exploration. Just like a blind date, the experience encourages us to observe with curiosity and view data collection as a chance to learn something new about our universe.
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