4015 Wilson–Harrington is an active asteroid known both as comet 107P/Wilson–Harrington and as asteroid 4015 Wilson–Harrington. It passed 0.4 AU (60 million km) from Earth on 20 July 2022 and then passed perihelion on 24 August 2022. It seldom gets brighter than apparent magnitude 16. It will return to perihelion on 25 November 2026.
4015 Wilson–Harrington at 19 November 1949, from the 48-inch Schmidt telescope at Palomar. The image was enhanced by ESO to show the tail.
Active asteroids are small Solar System bodies that have asteroid-like orbits but show comet-like visual characteristics. That is, they show a coma, tail, or other visual evidence of mass-loss, but their orbits remain within Jupiter's orbit. These bodies were originally designated main-belt comets (MBCs) in 2006 by astronomers David Jewitt and Henry Hsieh, but this name implies they are necessarily icy in composition like a comet and that they only exist within the main-belt, whereas the growing population of active asteroids shows that this is not always the case.
Asteroid 596 Scheila displaying a comet-like appearance on 12 December 2010
Dust ejecta and tail from the aftermath of the Double Asteroid Redirection Test's impact on the asteroid moon Dimorphos, as seen by the Southern Astrophysical Research Telescope in 2022
Disintegration of asteroid P/2013 R3 observed by the Hubble Space Telescope (6 March 2014).
Asteroid 101955 Bennu seen ejecting particles on January 6, 2019, in images taken by the OSIRIS-REx spacecraft