Abstract

On October 19, 2017 project Pan-STARRS discovered (for the first time) a macroscopic interstellar object traversing the inner part of our Solar System. Due to its high speed (about 26 km/s at infinity) and small size (several hundred meters), its observations were possible for only 40 days after the discovery. However, they presented us with many mysteries. In this presentation, I will talk about several of them, focusing on the physical nature of ‘Oumuamua. Despite the fact that it showed no direct signs of cometary activity (tail, coma, gas and dust emissions, etc.), a detection of its non-gravitational acceleration has been interpreted as a sign of cometary activity. I will explain why this cometary interpretation suffers from a variety of problems that make it very unrealistic. I will also talk about the theory for the origin of ‘Oumuamua, based on the assumption of its asteroidal nature. According to this model, such objects are formed during tidal disruption events of planets and asteroids orbiting white dwarfs. Signatures of such catastrophic events are known to us observationally (pollution of the atmospheres of white dwarfs with metals, compact discs around them), providing additional support to this idea. In this talk I will also cover the discovery and current status of observations of the second interstellar visitor to the Solar System, comet 2I/Borisov discovered on August 30 of this year.