4015 Wilson–Harrington is a small Solar System body known both as Comet Wilson–Harrington or 107P/Wilson–Harrington, and as an asteroid designated 4015 Wilson–Harrington.
It is considered both an Apollo asteroid with the designation 4015 Wilson–Harrington and a periodic comet known as Comet Wilson–Harrington or 107P/Wilson–Harrington. It was initially discovered in 1949 as an comet and then lost to further observations. Thirty years later it was rediscovered as an asteroid, after which it took over a decade to determine that these observations were of the same object. Therefore, it has both an comet designation and an asteroid designation, and with a name length of 17 characters it is currently the asteroid with the longest name, having one more character than the 16-character limit imposed by the IAU.
The comet was discovered on November 19, 1949, by Albert G. Wilson and Robert G. Harrington at Palomar Observatory. Only three photographic observations were obtained and the comet was lost (insufficient observations to determine a precise enough orbit to know where to look for future appearances of the comet, see Lost comet).
On November 15, 1979, an apparent Mars-crosser asteroid was found by Eleanor F. Helin, also of Palomar Observatory. It received the designation 1979 VA, and when re-observed on December 20, 1988, received the permanent number 4015.
On August 13, 1992, it was reported that asteroid (4015) 1979 VA and comet 107P/Wilson–Harrington were the same object. By then, enough observations of the asteroid had been accumulated to obtain a fairly precise orbit, and the search of old photographic plates for pre-discovery images turned up the 1949 plates with the images of the lost comet.
Although the 1949 images show cometary features, all subsequent images show only a stellar image, suggesting it may be an inactive comet that undergoes only infrequent outbursts.
The eccentricity is 0.624, which is somewhat higher than that of a typical asteroid-belt minor planet and more typical of periodic comets.
There are only four other objects that are cross-listed as both comets and asteroids: 2060 Chiron (95P/Chiron), Comet 133P/Elst–Pizarro (7968 Elst–Pizarro), 60558 Echeclus (174P/Echeclus), and 118401 LINEAR (176P/LINEAR). As a dual status object, astrometric observations of 4015 Wilson–Harrington should be reported under the minor planet designation.
A flyby of 4015 Wilson–Harrington was formerly planned by Deep Space 1. It was also considered for the NEAR mission.