When the fainting Comet 17P/Holmes erupted with the brightest cometary burst ever observed in October 2007, astronomers watched in awe. It was not the first time that this disappointing 2.1 mile wide (3.4 kilometer) course comet did it. In fact, the ice ball was only discovered thanks to a similar explosion in 1892.
Debris from the 2007 explosion, which at the time created a coma larger than the sunorbit always in the center solar systemperiodically crossing the trajectory of Earth. This month it may be visible to amateur telescopes, and a team of Finnish scientists are encouraging skywatchers to look for it, as the observations could help explain what’s so special about 17P/Holmes. The the best time to observe comet 17P/Holmes is after August 22 to avoid interference from the bright moon, amateur astronomers said.
Related: When to Look for Comet 17P/Holmes in the August Sky
“This comet is different from other comets because other comets have not produced such outbursts,” Markku Nissinen, a Finnish amateur astronomer who observed the 2007 outburst and studied the comet, told Space.com. 17P/Holmes since. “It’s a Jupiter family comet and there are hundreds of them but none of them have ever done this. There must be something different about this one.”
Comets of the Jupiter family orbit the sun in elliptical orbits with the farthest points between the orbits of March and Jupiter and the closest point to the star. They typically complete one orbit in about 20 years, lighting up each time they approach the sun. Due to these frequent visits to the central solar system, Jupiter-family comets become progressively fainter as the warm environment depletes the volatile materials responsible for creating their bright cometary tails.
But 17P/Holmes doesn’t follow that pattern, which Nissinen says suggests the comet may have a different chemical makeup than any other known Jupiter-family comets.
“It’s possible that this comet formed at a different place in the solar nebula,” Nissinen said.
Maria Gritsevich, a planetary scientist at the University of Helsinki in Finland who co-authored several studies of Comet 17P/Holmes with Nissinen, told Space.com that the comet strangely does not produce explosions during of each visit to the central solar. system.
“[These outbursts] always appear when the comet passes a short distance from the sun, so it seems related to heat,” Gritsevich said. “But the explosions don’t seem to be periodic. They’re pretty random.”
Gritsevich hopes that observations of debris flows could begin to answer some of these questions. By measuring the brightness of particles, their size and their distribution, astronomers can glean information about their physical and chemical properties.
Nissinen added that an infrared observatory, like the James Webb Space Telescopecould easily unravel the mysteries of 17P/Holmes by measuring the absorption spectra of the comet’s dust, which would reveal its chemical composition in great detail.
“The dust is well observable in the mid-infrared [wavelengths]”, Nissinen said. “If they could observe it from space with the James Webb Space Telescope, that would be really interesting.”
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