SO Colloquium: Interstellar planetesimals: 1I/Oumuamua and 2I/Borisov

Extensive surveys of extrasolar planets and of circumstellar disks around nearby stars show that planets and dust-producing planetesimals, similar to the asteroids, Kuiper belt objects and comets in our solar system, are ubiquitous around others stars. The planetesimal population of the young solar system was very numerous initially but the majority of the objects ended up ejected due to gravitational perturbations with the planets and other external perturbers. Numerical simulations indicate that many other planetary systems would have experienced a similar evolution, yielding to an interstellar space filled with ejected planetesimals. This is why, for decades, we had been puzzled that none of these interstellar planetesimals was ever detected crossing the solar system, even though it would have been easily identified as a hyperbolic comet. Then, when 1I/‘Oumuamua, the first interstellar interloper, was finally discovered, our puzzlement grew into utter bewilderment. From its detection with PanSTARRS, and taking into account the depth and duration of this survey, we can infer how many 1I/'Oumuamua-like objects are out there and this number, we will see, is at least ten times larger than what one would be expected from the ejection of planetesimals from extrasolar planetary systems, leaving unanswered the question of its origin. Furthermore, even though we would expect most of the ejected planetesimals to be icy, because the majority would originate from the outer regions of their parent systems, 1I/‘Oumuamua did not show evidence of any of the outgassing typical of solar system icy bodies, leaving unanswered the question of its composition. The discovery of 2I/Borisov, the second interstellar interloper, with an unquestionable cometary composition, has reassured us that a population of icy interstellar planetesimals exists. Similar to their crossing of our solar system, these interstellar planetesimals will also enter the environments where planet formation is taking place.

01/07/2021 - 12:30
Dra. Amaya Moro-Martín
Space Telescope Science Institute, Baltimore, Maryland, USA