Astronomy Picture of the Day

Explanation: Could this close-by asteroid ever hit the Earth? Eventually yes -- but probably not for a very long time, even though the asteroid is expected to pass inside the orbit of the Moon next century. However, to better understand the nature and orbit of all near-Earth asteroids, NASA sent the robotic Origins, Spectral Interpretation, 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 scheduled to map the minor planet's rough surface. The featured time-lapse video taken earlier this month compacts Bennu's 4.25-hour rotation period into about 7 seconds. Bennu's diamond-like appearance is similar to asteroid Ryugu currently being visited by the Japanese spacecraft Hayabusa2. The exact future orbit of Bennu is a bit uncertain due to close passes near the Earth and the Yarkovsky effect: a slight force created by an object's rotationally-induced, asymmetric infrared glow. If all goes according to plan, ORISIS-Rx will actually touch the asteroid in 2020, collect soil samples, and return them to Earth in 2023 for detailed analyses.