Minor planets are small solar bodies that orbit the sun and have gravity but are not influential enough. Asteroids are small and large rocky bodies with eccentric orbits found in the orbit between Mars and Jupiter. On the other hand, comets are small bodies of ice, dust and gas, which form a tail when travelling towards the sun. Comet Wilson–Harrington is one such unique celestial object that displays unique characteristics of all the three, namely a comet, an asteroid and a minor planet. Comet Wilson is closer to being a comet that exhibits sudden outbursts of brightness. But, it has the unique classification of a comet as well as a minor planet, which is an asteroidal–type.
Astronomers Albert George Wilson and Robert George Harrington of Palomar Observatory California, USA discovered this comet on a 48 inch Schmidt telescope. The comet was founded within the constellation of Pegasus. It was first observed on 18th November, 1949 on photographic plates exposed on the same date. Both the astronomers observed the comet again on the 22nd and 25th of November. The discovered comet was hence, named after the two astronomers Wilson and Harrington.
Observations made about this comet include:
- The comet had a less than one degree long tail.
- According to Leland E. Cunningham of Students’ Observatory California, the plates exposed on 19th and 22nd November, 1949 showed a small faint tail but no trace of coma (cloud of dust) and would have been called a minor planet, if exposed through a slower telescope.
- Leland observed an elliptical orbit and an orbital period uncertain by two years or more.
- On 15th November, 1979, Eleanor Helin (Palomar Observatory) noted a fast– moving asteroid–type object in the constellation of Pisces on plates exposed on 0.46 m through Schmidt telescope. The object was confirmed on 16th and it received a designation as 1979 VA minor planet and a permanent designation as 4015 minor planet.
- In 1992, E. Bowell (Lowell Observatory, Arizona, USA) observed the images of the plates of the minor planet 4015 on 19th November, 1949 and identified it with a tail (similar to a comet).
- Well known astronomer B. G Marsden studied all the apparitions from 1949 to1992 and linked them thus, making the comet and the minor planet one and the same celestial object.
- However, Marsden ultimately noted that the observation suggests that ‘the object is a largely inactive comet that undergoes occasional outbursts’.
On its discovery apparition in 1949, the magnitude of comet Wilson–Harrington was noted at 16 and 12. However, on its rediscovery as an asteroid–type object in 1979, the magnitude was revealed at 11.
Perihelion distance (near to the sun) of comet Wilson–Harrington is 0.991 AU while its aphelion distance (far from the sun) is 4.29 AU.
The orbital period of comet 107P/Wilson–Harrington (4015) is about 4.29 years.
Comet 107P/Wilson–Harrington (4015) was observed to be a very inactive comet. It was rediscovered as an asteroid in 1979 and was again observed as a minor planet in 1992.
The comet had no encounters but its orbit almost touches earth’s orbit at perihelion. Hence, it often approaches the earth.
Comet 107P/Wilson–Harrington 4015 is expected to reappear on 23rd May, 2018.
