The Right Navigation Camera (Navcam) on the Mars Perseverance rover recently took an image of comet 3I/ATLAS, revealing an elongated stripe that sparked debate about whether it’s a large cylindrical object or not. To clarify this, experts analyzed the camera’s sensitivity and angular resolution to estimate the length of the stripe.
According to NASA, 3I/ATLAS was approximately 38 million kilometers away from Mars when the image was taken. The Navcam has an angular resolution of 0.33 milli-radian per pixel, which translates to a spatial scale of about 12,500 kilometers at that distance. This means the projected length of the stripe is around 50,000 kilometers.
However, this value is significantly larger than the estimated diameter of 3I/ATLAS, which was derived from another space observatory as 46 kilometers for an albedo of 4%. The discrepancy suggests that the elongation is likely due to a long integration time used to make the composite image. This would have resulted in a streak of smeared images, rather than a single, long cylindrical object.
To support this conclusion, experts considered the speed of 3I/ATLAS relative to Mars and the Martian sky. The comet’s motion across the Martian sky would have caused smearing, which is much smaller compared to the limited angular resolution of Navcam.
In short, the elongated stripe in the image must be an artifact of a long integration time used to create the composite image. This means 3I/ATLAS was not visible as a single, elongated object but rather as a sequence of smeared snapshots taken over a short period.
Source: https://avi-loeb.medium.com/interpretation-of-the-stripe-in-the-new-image-of-3i-atlas-from-the-perseverance-rover-camera-7c5332c60ff1