In just one image, @NewHorizons2015 may have provided an important proof of “pebble accretion”. #UltimaThule’s contact binary shape is characteristic of this gentle formation. #UltimaFlyby @NASANewHorizons pic.twitter.com/xGFsQVnEbz

— James Tuttle Keane (@jtuttlekeane) January 2, 2019