4015 Wilson–Harrington

Lore & Background

The comet was discovered on 19 November 1949 by Albert G. Wilson and Robert G. Harrington at Palomar Observatory, but only three photographic observations were obtained, and the comet was lost due to insufficient data to determine a precise orbit. Thirty years later, on 15 November 1979, Eleanor F. Helin discovered an apparent Mars-crosser asteroid at Palomar, designated 1979 VA, which later received the permanent number 4015. On 13 August 1992, it was reported that asteroid (4015) 1979 VA and comet 107P/Wilson–Harrington were the same object, after enough asteroid observations had accumulated to compute a precise orbit and old photographic plates from 1949 were found showing the lost comet. Although the 1949 images show cometary features, all subsequent images appear stellar, suggesting it might be an inactive comet that undergoes only infrequent outbursts. Its eccentricity of 0.624 is higher than typical asteroid-belt minor planets and more typical of periodic comets. With a Minimum Orbit Intersection Distance (MOID) of less than 0.05 AU and its large size, it is classified as a potentially hazardous asteroid (PHA). It passed 0.4 AU (60 million km) from Earth on 20 July 2022 and then passed perihelion on 24 August 2022, and seldom gets brighter than apparent magnitude 16.

Reader's Guide

4015 Wilson–Harrington holds a unique place in solar system astronomy as one of only nine objects that are cross-listed as both comets and asteroids, alongside bodies such as 2060 Chiron and 7968 Elst–Pizarro. Its dual identity emerged from a decades-long observational puzzle: discovered as a comet in 1949 and lost, then rediscovered as an asteroid in 1979, it took until 1992 to confirm they were the same object. This history underscores the challenges of tracking small bodies with limited observations and the value of archival plate searches. As a potentially hazardous asteroid with a MOID under 0.05 AU, it is monitored for Earth impact risk. Its cometary activity appears sporadic, with only the 1949 images showing a coma, while later observations show a stellar appearance. The object was formerly considered for flyby missions by Deep Space 1 and the NEAR mission, highlighting its scientific interest. Astrometric observations of this dual-status object should be reported under the minor planet designation, per IAU practice.

Did You Know?

• 4015 Wilson–Harrington has the longest name of any asteroid at 17 characters, exceeding the 16-character IAU limit.
• It is one of only nine objects cross-listed as both a comet and an asteroid.
• The comet was discovered in 1949 but lost, then rediscovered as an asteroid in 1979, with the connection confirmed in 1992.
• It passed 0.4 AU from Earth on 20 July 2022 and will return to perihelion on 25 November 2026.

A Comet Lost and Found

The story begins in November 1949 at Palomar Observatory, where Albert G. Wilson and Robert G. Harrington captured just three photographic frames of a faint object before it vanished from view. Without enough data to pin down a reliable orbit, the comet was effectively lost to science. Three decades later, on 15 November 1979, Eleanor F. Helin—also working at Palomar—spotted what appeared to be a Mars-crossing asteroid, initially catalogued as 1979 VA. When it was re-observed in December 1988, it earned the permanent number 4015. The breakthrough came on 13 August 1992, when accumulated astrometric data allowed researchers to match the asteroid's orbit back to the 1949 plates. Those old images revealed unmistakable cometary features, confirming that the newly numbered asteroid and the long-lost comet were one and the same body. What had been two separate catalog entries for over forty years was finally unified under a single identity.

A Name That Broke the Rules

4015 Wilson–Harrington holds a peculiar distinction in the minor-planet catalog: its full name stretches to seventeen characters, making it the longest-named asteroid ever registered. The International Astronomical Union imposes a sixteen-character limit on asteroid designations, yet this object exceeds that boundary by one letter. The extra character is a direct consequence of its dual identity—astronomers had to honor both the comet designation (107P/Wilson–Harrington) and the asteroid number (4015) while preserving the names of its two 1949 discoverers. Only seven other bodies share this cross-listed status, including the well-known 2060 Chiron and 7968 Elst–Pizarro, bringing the total to eight objects that carry both a comet and an asteroid identity. For observational purposes, the rules are clear: astrometric measurements of this body must be reported under its minor-planet designation, even though its cometary heritage remains firmly embedded in its name and orbital character.

An Orbit That Crosses Worlds

The orbital path of 4015 Wilson–Harrington is markedly more elongated than that of a typical main-belt asteroid, with an eccentricity of 0.624—a value more in line with periodic comets. Its Minimum Orbit Intersection Distance with Earth's orbit is less than 0.05 AU, and combined with its large physical size, this qualifies it as a potentially hazardous asteroid. The object's 2022 passage illustrated the practical significance of that classification: on 20 July it swung within 0.4 AU, roughly 60 million kilometres, of Earth, then continued on to perihelion on 24 August of the same year. Despite these close approaches, the body rarely brightens beyond apparent magnitude 16, making it invisible to the unaided eye and detectable only with dedicated telescopic equipment. Its next perihelion passage is scheduled for 25 November 2026, at which point observers will again have a window to study this enigmatic dual-status object as it rounds the Sun.

A Comet That Chose Silence

The 1949 photographic plates captured by Wilson and Harrington clearly show cometary structure—evidence that the object was actively outgassing at the time of its discovery. Every subsequent observation, however, has revealed a point-like, stellar appearance with no detectable coma or tail. This stark contrast suggests that 4015 Wilson–Harrington may be an essentially dormant comet that produces visible activity only during rare, infrequent outbursts. The object's dimness—seldom exceeding magnitude 16—further complicates the task of catching it in an active state. Its scientific intrigue has drawn the attention of space agencies: a flyby was once incorporated into the Deep Space 1 mission plan, and it was also evaluated as a target for the NEAR spacecraft. Neither visit ultimately took place, leaving the question of whether this quiet asteroid is truly a sleeping comet to be answered by future observations or a dedicated mission yet to be conceived.