E. G. Rivera-Valentin, P. A. Taylor, A. Virkki, and B. Aponte-Hernandez report that Arecibo (2380 MHz, 12.6 cm) delay-Doppler radar images obtained on 2017 January 20 and 23 reveal near-Earth asteroid (163693) Atira is a binary system. Visible range extents of the components in images with 150 m/pixel resolution suggest a primary up to 4.8 ± 0.5 km in diameter and a secondary 1.0 ± 0.3 km in diameter.

Until this year, astronomers have only been able to indirectly determine the presence of gravitational waves -- tiny, wave-like shifts of space and time -- through the measurements of decaying orbits of neutron stars. In January 2016, the LIGO collaboration announced the first direct detection of gravitational waves from a system of black holes orbiting and colliding together. Read More