The Planetary Society’s Shoemaker NEO Grants fund efforts to find, track, and characterize near-Earth objects to help protect our planet from hazardous impacts. Many of our grant winners are skilled binary asteroid hunters. Two-time Shoemaker grant recipient Vladimir Benishek recently discovered 19 new binary asteroids over a 15-month span, using equipment he purchased through his 2018 and 2022 grant proposals. 

Binary asteroids rotate around their barycenter, or common center of mass. Some binary asteroids like Ida and Dactyl have lopsided size ratios, and one object orbits the other. 

Other binaries are closer in size, with one object still noticeably larger than the other. This is the case for Didymos and Dimorphos, which NASA’s DART mission targeted in its successful planetary defense test in 2022. 

When the Lucy spacecraft flew past asteroid Dinkinesh in 2023, it found that Dinkinesh had a smaller companion, which has since been named Selam. Selam is a contact binary: two objects that are touching each other. Another example of a contact binary is Arrokoth, the Kuiper Belt world visited by the New Horizons spacecraft in 2019.

Still other binaries are nearly equal in size, such as double asteroid 2017 YE5. An observatory that received Shoemaker grant funding made the initial discovery of 2017 YE5, while another Shoemaker winner helped confirm its double nature in 2018.