Goodbye ‘Oumuamua, Hello Borisov; This Is What Two Interstellar Interlopers Can Teach Us
“The most interesting aspect of what we know so far about interstellar objects is how different the first two, ‘Oumuamua and Borisov, truly are from one another. There are a number of ways to form interstellar bodies: from failed star systems in star-forming regions, from ejected asteroids, from comets, and from collisional debris. We do not know how common or rare objects of all these different types are, nor how to definitively classify the ones we’ve seen so far, but hope is on the way. Beginning in the 2020s, the Large Synoptic Survey Telescope will come online, expected to uncover dozens of such objects by 2030.
What are the size and frequency distributions of the interstellar population? How old and/or weathered are they? Are they comet-like or asteroid like; volatile-rich or volatile-free, and do different classes of object originate from different regions in the sky? Are most small objects inactive while most large ones are active? With the tip of the interstellar iceberg uncovered, the answers to these questions and more are at last within our reach.”
In our solar system, asteroids, centaurs, comets, Kuiper belt and Oort cloud objects all have their own unique story, but possess many qualities common to each separate class. Occasionally, one of these objects will get ejected, where it will wander the Milky Way indefinitely, until it encounters another object.
Back in our Solar System, we’ve begun discovering and identifying objects in our neighborhood that originated from interstellar space. In 2017, ‘Oumuamua became the first, and it was extremely odd: small, elongated, and already on its way out. Our picture is now changing dramatically, as a second interstellar object, 2I/Borisov, was just discovered.
With its closest approach coming in early December, astronomers worldwide are getting ready. Here’s what we know so far.