On October 17 and 18, 2017, an unusual object sped across the field of view of a large telescope perched near the summit of a volcano on the Hawaiian island of Maui.

While typical asteroids and comets in the Solar System orbit the Sun, ‘Oumuamua and Borisov are celestial nomads, spending most of their time wandering interstellar space.

More recently, computer models have shown that the Solar System sent its own population of smaller bodies into the voids of interstellar space long ago due to gravitational interactions with the giant planets.

Borisov fit this profile: It had a tail made of gases and dust created by ices that evaporated during its close passage to the Sun.

This suggests that it originated in the outer region of a planetary system where temperatures were cold enough for gases like carbon monoxide to have frozen into its rocks.

The gravity of a passing star can eject smaller bodies, known as planetesimals, from the outer reaches of a system, according to a recent study led by Pfalzner.

Saved 69% of original text.