On Wed, 25 Oct 2017 12:55:23 -0700 (PDT), palsing
wrote:

http://www.skyandtelescope.com/astro...stellar-comet/

Wow, this is fascinating...

"... an object swept up just a week ago by observers using the PanSTARRS 1 telescope atop Haleakala on Maui has an extreme orbit — it's on a hyperbolic trajectory that doesn't appear to be bound to the Sun. Preliminary findings, published earlier today [10/25/2017] by the International Astronomical Union's Minor Planet Center (MPC), suggest that we are witnessing a comet that escaped from another star."

To be clear, a number of comets, and possibly some meteoroids, have
been observed to have hyperbolic orbits. But these have always had
eccentricities just fractionally greater than one... explainable as
either measurement error or by the conversion of elliptical to
hyperbolic orbits due to gravitational perturbations. What makes this
object interesting is its very high eccentricity of 1.19. That's way
outside of measurement error, and it's far too high to reasonably
explain by interactions with the gas giants and Sun.