Even ordinary telescopes have a way of acting less ordinary when there comes a comet that will never be seen again. The object, named 3I/ATLAS, is the third confirmed interstellar visitor, following 1I/OMuamua and 2I/Borisov, and has not been approached as a target object as much as as a moving equalizer object in contemporary astronomy. The ATLAS survey in Chile was the first flagged and soon identified as unbound: a hyperbolic orbit, which is consistent with a point outside the Solar System. It was already traveling at about 137,000 mph when first identified, so its one-and-only trip, coupled with the direction it takes, would become a characteristic limitation to all planning to look at it.
That limitation has brought to the fore another form of engineering, coordination. The observations have been constructed on various points of view, near the earth, near Mars, and by spacecrafts never meant to observe interstellar comets, as none of the instruments alone can contain the entire tale. A case in point came with the Solar and Heliospheric Observatory which had no expectation of 3I/ATLAS seeing it at all, only by stacking images did the coronagraph data of SOHO show the comet as a faint brightening, as it crossed the field of view at about 222 million miles distance. The platform has also become a protracted example of distributed discovery, having been assisted by citizen scientists in transforming SOHO into the most fruitful object-discoverer of comets in history, with more than 5,186 comet discoveries to its image.
The pedigree of 3I/ATLAS is not the only reason to consider it scientifically useful, but that particular chemistry and dust behavior as it heats up. The James Webb Space Telescope conducted IR spectroscopy found that the coma was dominated by carbon dioxide with a calculated ratio of CO2/H2O of 7.6 +3.-0, an outlier to the usual Solar System comets of the same distance. Such an unstable combination is important since it alters the dynamics of action: what ices propel jets, what dust-grains are stirred and at what distance does the comet appear to view itself living. In visible-light observation Independent observers have reported several tails and a sun-pointing anti-tail, geometry that can be produced when dust grains of relative size are thrown sunward, and only diverted by radiation pressure very gradually. One of the estimates quoted has those grains approximately 100 microns round, which refigures the modeler thinking on the brightness and mass loss in the coma.
Metals have introduced a second more acute puzzle. A spectroscopy using the Very Large Telescope observed many neutral nickel lines but not iron, suggesting an efficient low-temperature release of nickel bearing material. Instead of requiring extreme heating, it is found favorable to the mechanisms which involve dust and photochemistry-paths which can be undertaken by a comet whose overall behavior is described by UCLA comet observer David Jewitt as It is doing the things comets do.
The tails of the comet also can be brought to serve as a sampling device. It was recently demonstrated by modeling that a positioning of the Sun, 3I/ATLAS and Europa Clipper can permit the spacecraft to traverse the solar-wind packets that have already collected cometary ions, which can be identified by heavier water-group elements, and by minute amounts of deceleration and bending of the flow. It is an uncommon type of experience: not a flythrough of dust, but a chemically marked wind which is essentially blowing a section of the comet away.
3I/ATLAS has served as a stress test on the way astronomy is currently run: fewer standalone hero observations, more wavelength, distance and institution choreography. It is not the mystery of it, but a momentary, quantifiable point of reference of what other systems make when they create comets, which makes the comet in that choreography its real gift.
