“Understanding ISO origins provides a deeper context for interpreting their physical and chemical properties,” noted Shokhruz Kakharov of Harvard University. Such remarks encapsulate the scientific curiosity associated with the passing comet 3I/ATLAS, which has been classified as only the third interstellar object to pass through the solar system. The object will pass closest to the earth on December 19 with a distance of 1.8 astronomical units or about 270 million kilometers.
Discovered on July 1 by the ATLAS telescopes in Chile, which are funded by NASA’s ATLAS program, 3I/ATLAS’s hyperbolic-orbit trajectory assures a permanent celestial exile and will keep the object from ever returning to our solar system again. Similar to its antecedents 1I/‘Oumuamua and 2I/Borisov before it, the trajectory and speed of 3I/ATLAS make its clear origin beyond the solar system’s influence impossible to deny. These interstellar objects are known to emerge from the cooler outer reaches of protoplanetary systems surrounding other stars and to be flung into interstellar space by gravitational interactions possibly with giant planets whose migration and subsequent dynamics of scattering may lead to the ejection of enormous cometary populations into interstellar space to wander the galaxy as interstellar objects. The solar system’s own formation may have seen as much as Earth’s mass 30 times worth of comet material ejected into the galaxy during the giant planets’ migration outwards from the central solar system near birth.
Initial observations with the James Webb Space Telescope of the 3I/ATLAS comet suggest a nucleus composed of carbon dioxide ice. This particular volatile evaporates well below the freezing point of water, indicating that the formation site of the 3I/ATLAS comet must have been more distant from the parent star compared to regular solar system comets that contain a higher amount of water ice. This data is also indicative of a similarity in chemistry among 2I/Borisov and 3I/ATLAS, considering that the former had a level of carbon monoxide that indicated it must have formed in cold environments.
The interstellar travel history of the comet, in the galaxy, is an added observational understanding. The research by Kakharov and Abraham Loeb on the Monte Carlo simulations, by the name GalPot, was used to reverse the orbit of the three known interstellar comets. The research shows that 3I/ATLAS is the oldest of the three comets, has a median age of 4.6 billion years, and was formed in the Milky Way’s thick disk, a set of older, lower-metallicity stars that are distinct from the Sun’s thin disk, neighbourhood. This is contrastingly younger than ‘Oumuamua and Borisov, showing that interstellar comets are released at various times in the galaxy, and not only in newly formed galaxies.
In terms of engineers and observers, this is a distinguishing opportunity for cometary calibration. Many instruments, such as the Hubble Space Telescope and ESA’s JUICE, already have images of 3I/ATLAS making its rapid approach towards the sun, and earth-based observatories are preparing for a data-intensive opportunity during its optimal resolution during closest approach. On this topic, it is also believed that future projects such as the Vera C. Rubin Observatory’s Legacy Survey of Space and Time could increase this amount by dozens per year once initiated and operational, with probes such as ESA’s Comet Interception attempting in-situ analyses.
The processes that lead these objects to be on escape orbits are a consequence of giant planet migration theories. When giant planets migrate through orbit changes, whether it is due to planetesimal migration or the “jumping-Jupiter” type of rapid migrations, they will eject ice objects with speeds in excess of the system’s escape speed. Sometimes, when these ice objects make close approaches to a giant planet’s tide disruption zone, they will break apart larger planetesimals into smaller fragments, with shapes like that of ‘Oumuamua. The efficiency of these ejections depends on the planet’s mass, orbital radius, or Safronov number, the planet’s efficiency in ejecting or accreting objects.
Amateur astronomers will witness the passing of a visitor to our neighborhood with relative easy access, powerful binoculars or a telescope being all that is needed on a moonless night. For scientists, it will offer a brief but highly informative insight into the physics and chemistry of planets that formed in a completely different star system. Each photon that reflects from 3I/ATLAS tells us a message about the conditions that existed billions of years and trillions of kilometers away, and how our own solar system’s history fits into the larger story of our galaxy.
