AstronomyPicture of the Day—20181122

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2018 November 22

TheUnexpected Trajectory of Interstellar Asteroid 'Oumuamua

ImageCredit: NASA, JPL, Caltech

Explanation:Why is 'Oumuamua differing from its expected trajectory? Last year, 1I/2017 U1'Oumuamua became the first known asteroid from interstellar space to passthrough our Solar System. Just over a year ago, this tumbling interstellar rockeven passed rather close to the Earth. The asteroid's future path should havebeen easy to predict given standard gravity -- but 'Oumuamua's path has provento be slightly different. In the featured animation, 'Oumuamua is shownapproaching and exiting the vicinity of our Sun, with the expectedgravitational and observed trajectories labelled. The leading naturalhypothesis for this unexpected deviation is internal gas jets becoming activeon the Sun-warmed asteroid -- but speculation and further computer simulationsare ongoing. 'Oumuamua will never return, but modern sky monitors are expectedto find and track similar interstellar asteroids within the next few years.