Blind dates are exciting because they hold the potential for surprises, especially when dealing with an interstellar date partner of unknown origin.
On October 3, 2025, the interstellar object 3I/ATLAS will pass within a distance of 29 million kilometers from Mars. At that time, the HiRISE camera onboard the Mars Reconnaissance Orbiter will be able to image 3I/ATLAS with a resolution of 30 kilometers per pixel. The resulting closeup image might separate the contributions of the nucleus and surrounding dust cloud to the total luminosity of reflected sunlight stemming from 3I/ATLAS.
The Minimum Orbit Intersection Distance (MOID) of 3I/ATLAS from Mars, namely the closest distance that 3I/ATLAS gets to the complete path of Mars around the Sun, is merely 2.7 million kilometers. This by itself constitutes a remarkable fine-tuning of the path of 3I/ATLAS.
If 3I/ATLAS is a technological object, this short MOID makes it easy for a precursor mini-probe to reach Mars. In addition, an orbit correction by 10–15 kilometers per second during the month of September 2025, could shrink the closest approach distance of 3I/ATLAS from Mars to zero, as calculated in Figure 4 of my paper with Adam Hibberd and Adam Crowl (accessible here).
The ejection of icy fragments from the surface of a natural comet can only result in a velocity kick of order 0.4 kilometers per second based on the analysis of data from the Webb telescope (accessible here). This ejection speed is insufficient for these fragments to reach Mars. Moreover, the extent of the CO2 plume observed by SPHEREx around 3I/ATLAS (as reported here) is of order 350,000 kilometers, a distance beyond which the plume is expected to be confined by the ram-pressure from the solar wind. This distance is still shorter by a factor of a hundred from the value needed to reach Mars during the closest approach of 3I/ATLAS without a maneuver. Given all these considerations, the arrival of materials from 3I/ATLAS to Mars in October 2025 will be a potential signature of technology.
Gladly, the Labor Day holiday provided me with a relief from my routine administrative duties as director of Harvard’s Institute for Theory & Computation. In between interviews for television and podcasts, I calculated that if 3I/ATLAS has a precursor probe that was traveling ahead of it and sideways towards Mars by about 30 million kilometers, then this precursor probe would be able to intercept Mars on October 3, 2025 or during the week preceding it.
This provides a second motivation for using HiRISE within a month. In addition to imaging the nucleus and dust cloud of 3I/ATLAS, HiRISE could image Mars in search for any precursor objects that precede 3I/ATLAS and get closer to Mars than the main object. Near-Earth telescopes cannot detect the reflection of sunlight from precursor objects that are smaller than a hundred meters, the upper limit on the size of all space probes launched by humans so far.
Blind dates can be exciting if we observe the other side with curiosity and regard data collection as an opportunity to learn something new.
ABOUT THE AUTHOR
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.