Have you heard of the comet named 109P/Swift-Tuttle? While the P denotes that it is a periodic comet (orbital period less than 200 years), Swift-Tuttle corresponds to the two individuals who simultaneously discovered the comet, days within each other.
Comets are usually named after their discoverer or based on the telescope or observatory that was used in the discovery. In this comet’s case, however, Lewis Swift discovered it on July 16, 1862, and Horace Parnell Tuttle independently did the same on July 19, 1862. It was only fair, therefore, that the comet be named after both of them.
Taking 133 years to orbit the sun once, Swift-Tuttle is a large comet with a nucleus that runs 26 km across. A ball of dust, ice, rock and dark organic material like any other comet, this one follows a very steep incline when compared to planets in the solar system.
As a result, this comet gathers a lot of speed when it passes the earth as it dives down into the solar system to get close to the sun and out again. In fact, the spectacular Perseid meteor shower that is witnessed every August, peaking in mid-August, is created by the dust and debris left by the Swift-Tuttle.
Despite the comet taking 133 years to pass by the earth, the meteor shower, which is among the most popular for viewers in the northern hemisphere, happens every year as a result of the earth moving through the trail of the comet’s orbit. This link between the comet and the meteor shower was discovered within three years of the comet’s discovery – by Giovanni Schiaparelli in 1865.
Catastrophic prediction
While all was well for over a century after its discovery, a catastrophic prediction was made in 1973.
With the limited observational data available and based on calculations on the comet’s orbit, astronomer Brian Marsden at the Harvard-Smithsonian Center for Astrophysics predicted that Comet Swift-Tuttle could collide with the earth in 2126.
Observation in 1992
This meant that observing the comet during its approach in 1992 became all the more important. With the technology at their disposal, astronomers were able to obtain accurate measurements when it was last seen. Based on this data, and incorporating complex calculations to account for the gravitational effects of sun and the other planets on the comet, a revised model for its motion was obtained.
The sighting in 1992, along with data from previous close approaches to the earth, allowed the astronomers to convince themselves beyond doubt that the collision in 2126 will indeed be impossible. That said, however, it is also not possible to rule out the collision forever.
Very small chance
Though highly unlikely, there is very small chance for this event to take place due to small influences on the comet every time it swings by the sun, altering its orbit. While Swift-Tuttle is indeed too massive to be affected this way, it is hard to predict how these effects add up over thousands of years. With further advances in our studies, perhaps, our answers could be more precise. And you could certainly have a say in those answers!
