On October 4, 2025 on the imply native photo voltaic time of 21:33:39 on Mars, the Proper Navigation Digital camera (Navcam) onboard NASA’s Mars Perseverance rover took a picture (posted on-line by NASA right here and right here) of the interstellar object 3I/ATLAS within the Martian sky. At the moment, 3I/ATLAS was at a distance of about 38 million kilometers from Mars.
The picture exhibits an elongated stripe which is about 4 occasions longer than it’s extensive. This stripe raised questions on social media as as to if 3I/ATLAS is a big cylindrical object. I used to be requested for my opinion about this puzzling picture by Rep. Anna Paulina Luna and so I instantly labored out the next numbers.
The Navcam on the Perseverance rover has sensitivity to seen mild with an angular decision of 0.33 milli-radian (or equivalently 68 arcseconds) per pixel, as detailed right here. This interprets to a spatial scale of about 12,500 kilometers on the distance of 3I/ATLAS from Mars when the picture was taken. This scale units the width of the elongated stripe within the Navcam picture of 3I/ATLAS. Thus, the projected size of the stripe is about 50,000 kilometers.
The higher certain on the diameter of 3I/ATLAS was derived by the SPHEREx area observatory (reported right here) as 46 kilometers for an albedo of 4%. The Navcam stripe is a thousand occasions longer than this higher restrict and subsequently should be an artifact of an extended integration time on condition that the supply strikes throughout the Martian sky. If 3I/ATLAS was a cylinder so long as 50,000 kilometers, then it will have occupied an angular dimension of 23 arcseconds within the Hubble Area Telescope picture taken on July 21, 2025, when 3I/ATLAS was at a distance of three occasions the Earth-Solar separation from the Hubble digital camera. As a substitute, 3I/ATLAS seems smaller by no less than an order of magnitude within the precise Hubble picture (accessible right here and right here). This means that the elongation of the stripe was generated by the mixing time used to make the composite Navcam picture, throughout which 3I/ATLAS moved throughout the Martian sky.
Mars orbits the Solar at a pace of 24 kilometers per second. 3I/ATLAS is touring on a retrograde orbit in the other way to Mars at a pace of about 67 kilometers per second relative to the Solar. The pace of 3I/ATLAS relative to Mars interprets to a path size of about 50,000 kilometers for an integration time of order 10 minutes.
In conclusion, the stripe within the Navcam picture will need to have resulted from stacking a whole lot of Navcam photographs over a complete time interval of about 10 minutes. 3I/ATLAS would have seemed like a round spot for a person snapshot, which has a most publicity time of three.28 seconds for Navcam. In a single body, the movement of 3I/ATLAS on the Martian sky would have smeared its picture by merely 300 kilometers, solely ~3% of the a lot bigger smearing by 12,500 kilometers related to the restricted angular decision of Navcam. The stacking of a whole lot of photographs enhanced the obvious brightness of 3I/ATLAS within the ultimate picture.
A method to consider the stripe is as a sequence of smeared snapshots, like a pod of inexperienced beans. 3I/ATLAS shared the expertise of a film star with a number of cameras from 7 Mars orbiters and a ground-based rover taking snapshots of it because it handed throughout the Martian sky.
The best decision picture was taken by the HiRISE digital camera onboard the Mars Reconnaissance Orbiter. HiRISE has an angular decision that translated to 30 kilometers per pixel on October 3, 2025. The brightest pixel within the HiRISE picture will present the perfect constraint but on the world of 3I/ATLAS. We’re all hoping that the HiRISE staff will launch their photographs as quickly as attainable.
ABOUT THE AUTHOR
Avi Loeb is the pinnacle of the Galileo Venture, founding director of Harvard College’s — Black Gap Initiative, director of the Institute for Idea and Computation on the Harvard-Smithsonian Heart for Astrophysics, and the previous chair of the astronomy division at Harvard College (2011–2020). He’s a former member of the President’s Council of Advisors on Science and Know-how and a former chair of the Board on Physics and Astronomy of the Nationwide Academies. He’s the bestselling creator of “Extraterrestrial: The First Signal of Clever Life Past Earth” and a co-author of the textbook “Life within the Cosmos”, each printed in 2021. The paperback version of his new e book, titled “Interstellar”, was printed in August 2024.
About The Author
