Imaging shows that much of the ejected material is in the form of dust particles. NASA indicated that the two missions to asteroids, Lucy and Psyche, were particularly helpful here, as they were further away from the Sun than 3I/ATLAS, and could therefore capture backlit images of the comet’s coma.
NASA’s Tom Statler, chief scientist for Solar System objects, said the amount of material ejected by 3I/ATLAS is fairly typical of Solar System comets. But some details are a little unusual. For example, the ratio of carbon dioxide to water is greater than that emitted by local comets. They usually emit iron and nickel together, but 3I/ATLAS appears to be unusually nickel-rich. So, there are signs that it has a history that is somewhat different from the comets in our solar system.
That history is difficult to understand. 3I/ATLAS came from the direction of the galactic core, and does not appear to have recently interacted with any other stars. If this is correct, it is possible that the object is older than the Solar System, and came from a star that formed relatively early in the history of the universe, and thus contained very few heavy elements.
For now, NASA has put up a webpage with a large collection of images from 3I/ATLAS and will update the site as more photos become available. But scientists on the call today stressed that it is still very early in the analysis, and some of these ideas may be refined as they make their way through discussion among scientists and peer review in journals.
Fox also explained that we were able to quickly identify and characterize 3I/ATLAS’s orbit in part because we have systems in place to identify any objects that pose a threat to Earth as part of our planetary defense program. With that and other automated surveys, it’s likely that the three objects we’ve observed so far (two comets, one asteroid) will gradually be joined by other objects, and we’ll be able to build a clearer picture of what’s floating among the stars.