If you’re as old as I am you have reason to be skeptical about comets. Comet Kohoutek in 1973 and the much anticipated return of Comet Halley in 1986 both failed to live up to their potential. But ISON may yet redeem the genre and prove spectacular:
Discovery News — NASA’s Mars Curiosity rover also may get a look when the comet sails past the red planet in early October.
The comet’s journey likely started in the Oort Cloud, a cluster of icy rocks that circle the sun about 50,000 times farther away than Earth’s orbit. Comet ISON is expected to pass as close as 700,000 miles, or 1.1 million kilometers, from the sun on Nov. 28.
If it survives, the comet could be the brightest to appear in Earth’s skies since 1965 and could even be visible in daylight.
Kohoutek was a long period comet thought to visiting the inner solar system for the first time. It was believed the tiny rocky nucleus would be encased in volatile ices that had never been heated and thus there would be enormous amounts of material available to form a glowing tail. For some reason it did not produce the hoped for effect. Comet Halley is a short period comet that visits about every 76 years. But in 1986 its orbit traced out a path far away from earth during the period of greatest brightness.
I still haven’t seen an orbit for ISON and it may be the same spectacular comet that appeared 300 years ago. But skywatchers say it will be less than a million miles from the sun’s surface at closest approach, plenty of time for surface ices to boil off even if they are under a thin layer of insulating substances. In fact the biggest threat to ISON is it will calve into pieces or disintegrate completely before making its way back into the dark distant depths in which it spends the vast majority of its life.