Theoretical modelling presented at the National Astronomy Meeting this week finds that the gravitational effects of gas giant Jupiter can influence the orbit of Comet Halley in such a way as to give periodically enhanced meteor displays.

Comet Halley has been observed and documented by astronomers since 240 BC, orbiting the Sun every 76 years. Earth crosses Halley’s path twice per orbit giving two meteor displays – the Orionids in October and Eta Aquariids in May – created by the comet’s dust particles burning up in our planet’s atmosphere.

Aswin Sekhar of Armagh Observatory told conference attendees that the periodic gravitational effects of Jupiter can constrain the orbit of Comet Halley along with particles outgassed from the comet that makes the so-called Orionid Stream and associated meteor shower.

“The comet gets trapped in a resonance, which increases the chances of meteoroid particles getting trapped in the resonance, giving enhanced meteor rates in particular years,” says Shekhar. “The success of the theoretical modeling seems to perfectly match historical observations, for example the Orionid outbursts in 1839, 1916 and 1993.”

Sekahr’s model covers the last 12,000 years, finding that from 1404 to 690 BC the comet was trapped in a 1:6 resonance with Jupiter, meaning that for every one orbit of Halley, Jupiter completed six orbits around the Sun. Later, between 240 BC and 1700 AD, the comet occupied a 2:13 resonance, and cometary debris deposited during these two periods has lead to enhanced activity during the Orionids meteor showers in some subsequent years. For example, Sekahr says that the unusual 1993 Orionid outburst was attributed to comet particles ejected from Halley in 240 BC.

“For the future we would expect similar activity in 2070, and an enhanced spectacular shower,” predicts Sekahr.

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