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The Kuiper belt region beyond the cold and distant planet of Neptune teems with millions of celestial objects called comets. Made up of ice, gas and dust, these comets may be remnants of the mysterious origin of the Universe. One such comet is comet 103P/Hartley 2, which is also known as a ‘weird’ dwarf comet due to its small size. Pioneer space agency NASA described comet Hartley as ‘a hyperactive little comet spewing more water than most comets its size’. This comet has received a visit from NASA mission EPOXI in 2010. Ranked as 103, it is a short–period comet of the Jupiter family and may herald a new breed of comets.

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Who discovered comet 103P/Hartley 2?

Astronomer Malcolm Hartley working with the UK Schmidt Telescope Unit of the Siding Spring Observatory, New South Wales, Australia discovered this comet. The comet was exposed on photographic plates. The photographic plates were exposed on 15^th, 17^th and 20^th of March, 1986. Astronomer Hartley noticed a diffused tail on one of the plates. Hence, a new comet was discovered. Malcolm Hartley announced his discovery to the Central Bureau of Astronomical Telegrams. As astronomer Hartley had discovered it, the comet was named as Hartley.

What were the observations made about this comet?

Observations made about this comet 103P/Hartley 2 include:

Astronomer D. W. E Green (Central Bureau of Astronomical Telegrams) made an initial observation and computed an uncertain parabolic orbit for the comet.
B. G Marsden calculated that the comet had passed perihelion on 4^th June, 1985.
He also noted that the distance of the comet from the sun was too small to make observations in 1985.
The composition of gases in comet Hartley includes a large amount of carbon dioxide or monoxide.
The diameter of its nucleus was small in size, which is only 2.2 km.
It takes about 18.1 hours for one complete rotation.

What was the magnitude noted?

At its discovery apparition, the magnitude of comet 103P/Hartley was noted at about 17–18. It reached a magnitude of 18 around 5^th April. In the 1991 apparition, comet Hartley was bright at a magnitude of 11 in early July and by the end of July, it reached a magnitude of 10. The 2010 apparition was the most favourable as the comet reached a magnitude of 7.5 –4.5 and became visible to the naked eye in the dark skies.

What is its perihelion distance?

Perihelion distance (closest to the sun) of comet 103P/Hartley is noted at 1.05 AU. The aphelion distance (far from the sun) of this comet is noted at 5.87 AU. The perihelion and aphelion distances change due to the gravitational effects of the giant planet Jupiter.

What was the orbital period noted?

The orbital period of comet 103P/ Hartley is noted at 6.46 years.

Did the comet reappear or was it recovered?

Comet Hartley was accidently rediscovered on 9^th July, 1991. Astronomer G. R Kastel (Institute for Theoretical Astronomy) reported and confirmed this rediscovery made by astronomer T. V Kryachko (Majdanak). Astronomer Nakano, who had predicted comet Hartley’s return for 1992, confirmed that this comet was 103P/Hartley 2. The comet was recovered on 2^nd May, 1997 at Whipple Observatory, Mt. Hopkins.

Did it encounter any other planet?

Comet 103P/Hartley had close encounters with Jupiter in August 1947, 28th April, 1971 and 2^nd November, 1982. It had close approaches to the earth in 1991, 1997 and 2010.

Is it expected to reappear?

Comet 103P/Hartley is expected to reappear or pass perihelion on 20^th April, 2017. Its last perihelion was on 28^th October, 2010.

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