Often seen as bright and pristine messengers of remnants from the past, comets are balls of ice, dust and water. Originating from the Kuiper belt beyond Neptune, comet Borrelly is also considered a relic of the past. Most of them reflect sunlight in their perihelion position but the comet Borrelly appears dark. This complex appearance of the comet still amazes astronomers. In its 2001 apparition, comet Borrelly was visited by mission Deep Space 1. Probe revealed jets emanating from the bright patches on its surface, which were eroding the surface. This erosion is likely to split the comet into two. It is a periodic comet and belongs to the Jupiter family.
Comet 19P/ Borrelly was discovered on 28th December, 1904. Alphonse Louise Nicholas Borrelly (Marseilles, France) discovered it during a routine search for comets. It was located in the constellation of Cetus. This comet was the 19th comet whose orbit could be determined and is hence, named as 19P/Borrelly, after Alphonse Borrelly, the astronomer who discovered it.
Following observations were made about comet 19P/ Borrelly:
- Comet Borrelly appeared to be a dark comet, unlike other comets, which appear bright and its shape resembled a bowling pin.
- It had a small faint nucleus. Close images confirmed its nucleus as dark, long, mottled and dry.
- Images also showed jets of gas and dust, actively vaporising gas and a high temperature.
- The head and tail of the comet had a diameter of nearly 2 arc minutes and a length of 10 arc minutes respectively.
Observation of the comet Borrelly in January, 1905 revealed a magnitude of about 9, which declined to 14.5 in May. An apparition in 1911 revealed a magnitude of 13 which reached 8.4.
Perihelion distance of comet 19P/ Borrelly is noted at about 1.395 AU. On the other hand, the aphelion distance was noted at 5.83 AU. However, these distances keep changing due to the gravitational pull and push of the giant planet Jupiter.
The orbital period of comet 19P/ Borrelly is noted at about 6.91 years. However, earlier readings showed an orbital period of around 7.30 years. The orbital period changes due to the perturbations caused by the gravity of giant planet Jupiter.
19P/ Borrelly comet was recovered on 20th September, 1911. H. Knox Shaw and Alexandre Schaumasse were able to recover the comet based on predictions made by G.Fayet at Paris Observatory, France. The comet was not detected in its 1939 and 1946 returns but Elizabeth Roemer managed to photograph the comet in poor conditions in 1953. Roemer’s recovery also enabled an early recovery of comet 19P/Borrelly in 1960 and 1970 returns.
Comet Borrelly had six approaches to the earth and two close encounters with Jupiter in the 20th century. In the first half of 21st century, it is expected to make two close approaches to theeEarth and one close encounter with Jupiter.
Comet 19P/ Borrelly is expected to pass perihelion or reappear in 2022 and December, 2028. Its last perihelion was in May, 2015.
