Free Astronomy Magazine November-December 2023

NOVEMBER-DECEMBER 2023 T his artist’s impression illustrates an interstellar object rapidly approaching our Solar System. The object, ejected from its home planetary system long ago, traveled through interstellar space for billions of years before briefly passing through our cosmic neighborhood. Rubin Observatory will reveal many of these previously unknown interstellar visitors. [Rubin Observatory/NOIR- Lab/NSF/AURA/J. daSilva/ M. Zamani] With the aid of observations of our Solar System and computer simula- tions, scientists speculate that the gravity of larger planets and passing nearby stars often launches most of these remnant planetesimals away from their home systems and out into their galaxies. Traveling through space and not bound to any star, they’re now known as interstellar objects. “Planetary systems are a place of change and growth, of sculpting and reshaping,” said Ban- nister. “And planets are like active correspondents in that they can move trillions of little tiny planetes- imals out into galactic space.” If planets are the correspondents, in- terstellar objects are the telegrams containing valuable information about distant planetary systems and how they formed. And for a short time, some of these messages from afar are right in our cosmic backyard. “A rock from another solar system is a direct probe of how planetesimal formation took place at another star,” said Bannister, “so to actually have them come to us is pretty neat.” Though astronomers think many interstellar objects exist, and likely pass through our Solar System on a regular basis, only two have been confirmed: ‘ Oumuamua in 2017 (also known as 1I/2017 U 1 ), and the comet 2I/Borisov in 2019. These were discovered thanks to great timing, a lot of effort, and a little luck — these small, faint interstellar travel- ers are only visible when they’re close enough to see, and when our telescopes are pointing in the right place at the right time.