AstronomyPicture of the Day—20181115

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.

2018November 15

ImageCredit: NASA, GSFC, U. Arizona

Explanation:Could this close-by asteroid ever hit the Earth? Eventually yes -- but probablynot for a very long time, even though the asteroid is expected to pass insidethe orbit of the Moon next century. However, to better understand the natureand orbit of all near-Earth asteroids, NASA sent the robotic Origins, SpectralInterpretation, Resource Identification, Security, Regolith Explorer(OSIRIS-REx) to investigate this one: the 500-meter across asteroid 101955 Bennu.Launched in 2016, OSIRIS-REx is now approaching Bennu, and is first scheduledto map the minor planet's rough surface. The featured time-lapse video takenearlier this month compacts Bennu's 4.25-hour rotation period into about 7seconds. Bennu's diamond-like appearance is similar to asteroid Ryugu currentlybeing visited by the Japanese spacecraft Hayabusa2. The exact future orbit ofBennu is a bit uncertain due to close passes near the Earth and the Yarkovskyeffect: a slight force created by an object's rotationally-induced, asymmetricinfrared glow. If all goes according to plan, ORISIS-Rx will actually touch theasteroid in 2020, collect soil samples, and return them to Earth in 2023 fordetailed analyses.