Scientist John Bortle developed a model that could predict the life of a comet.
REPUBLIKA.CO.ID, JAKARTA — A new long-period comet has been discovered approaching the inner solar system. Astronomers calculated the orbits and found that the new comet would pass close to our sun, in the orbit of Mercury.
All indications suggest the comet is getting brighter, at least bright enough to be seen with binoculars, after its perihelion, or approaching the sun. However, will the comet orbit the sun or will the comet be destroyed? Not sure yet.
In July 1991, John Bortle, an amateur astronomer from the United States, developed a model that can be used to predict whether a comet will survive past its perihelion or closest point to the sun.
This model is known as comet Bortle’s survival limit. This method is still an invaluable tool for comet researchers and those hoping to catch a glimpse of comets.
What did John Bortle do?
Bortle studied 85 comets discovered from 1800 to 1989. The sun is within 0.5 astronomical units (AU). That is, comets come within half the distance between Earth and the sun, or less. Four of them are short-period comets that orbit the sun in less than 200 years.
The remaining 81 comets are long-period comets that take more than 200 years to orbit the sun. He recorded the results of each of the 85 comets.
As they approached the sun, sixteen of them were crushed. Six more comets managed to reach perihelion, but they became unstable and faded significantly. The remaining comets survived perihelion.
Bortle then looked at the absolute magnitude of each comet. The absolute magnitude of a comet is a measure of its true brilliance (in this case, how bright the comet is if it is one AU away from the Earth and the Sun).
Bortle identified the relationship between perihelion distance and absolute magnitude (brightness at 1 AU) (closest point to the sun). He discovered that comets that were intrinsically fainter did not survive as they approached the sun.
At such a perihelion distance, a brighter comet might survive. On the other hand, a weak comet will disintegrate at the same distance from the sun.
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