The latest research found that comets from outside the solar system originally ran away from the solar system!

Comets from outside the solar system, some of them originally ran away from the solar system! Astronomers from the National Astronomical Observatory of Japan (NAOJ) analyzed the paths of two celestial bodies that left the solar system forever and determined that they were likely to come from outside the solar system. These results improve our understanding of the outer solar system and interstellar space beyond. Not all comets orbit the sun in closed orbits, some travel through the solar system at high speeds before flying into interstellar space and never come back. While it is simple to calculate where these comets are going, it is more difficult to determine where they came from.

There are two possible scenarios: In the first, a comet was initially in a stable orbit far from the Sun, but a gravitational interaction with a passing body pulled the comet out of its orbit. The comet then fell into the inner Solar System, where it could be observed before being ejected into interstellar space. In the second scenario, a comet originated somewhere far away, perhaps in a different planetary system, and as it flew through interstellar space, randomly passed through the Solar System once and then continued on its way. Astronomers Arika Higuchi and Eiichiro Kokubo of the National Astronomical Observatory of Japan calculated the types of trajectories that would typically be expected in each scenario.

The team then compared their calculations with observations of two unusual outbound objects, 1i/'Oumuamua, discovered in 2017, and 2i/Borisov, discovered in 2019. The study found that the interstellar origin hypothesis provided a better match for the paths of these two objects. The study also showed that gas giants passing through the vicinity of the Solar System could have destabilized long-orbit comets and placed them in orbits similar to these two objects. Observations have not yet revealed any gas giants that can be linked to these two outbound objects. But further theoretical and observational studies of small interstellar objects are needed to better determine the origins of these objects.

The results of their study were published in the Monthly Notices of the Royal Astronomical Society. The dynamical properties of objects on hyperbolic orbits through the inner Solar System were studied in the context of two different origins: interstellar space and the Oort Cloud. The probability distributions of the eccentricity e and perihelion distance q were analytically derived for each origin, and the number of objects produced per unit time was estimated as a function of these quantities. By comparing the numbers from the two sources, it is possible to assess which origin is more likely for a hyperbolic object with a given eccentricity and perihelion distance. The study found that the probability of a given hyperbolic object's interstellar origin increases with decreasing eccentricity and perihelion.

Conversely, the probability that a hyperbolic object was scattered from the Oort Cloud by a passing star increases with decreasing eccentricity and increasing perihelion. By carefully considering the elements of their orbits, it is concluded that both 1I/2017U1'Oumuamua (e≃1.2 and Q≃0.26Au) and 2i/2019Q4 Borisov (e≃3.3 and Q≃2Au) are most likely of interstellar origin rather than being scattered from the Oort Cloud. However, the researchers also found that Oort Cloud objects can be scattered by substellar or even sub-Jovian mass perturbators into hyperbolic orbits like the two known examples mentioned above. This highlights the need to better characterize the low-mass end of free-floating brown dwarfs and planets.

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Bo Ke Yuan | Research/From: National Astronomical Observatory of Japan

Reference journal Monthly Notices of the Royal Astronomical Society

DOI: 10.1093/mnras/stz3153

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