One of the most amazing celestial displays visible to the naked eye on Earth is the passing of a comet near our atmosphere. This event is rare, but spectacular when casual observers are able to view what is known as a great comet, which is a comet that becomes exceptionally bright and can easily be viewed through Earth’s atmosphere. 1996 was to be a special year for the viewing of a great comet. Comet Hale-Bopp was passing through the solar system and promised an amazing show, but unbeknownst to the astronomical world, 1996 would yield yet another great comet.
January 31st, 1996, amateur astronomer, Yuji Hyakutake, was looking into the night sky in search of comets. This had been Hyakutake’s practice for years. He had even moved to a rural southern Japanese province in order to better view the night sky. Using a powerful set of binoculars, Hyakutake had discovered a comet two weeks prior and was again scanning in a similar area in order to track the comet’s progress. While peering into the vast expanse, he noticed a new body. Hardly believing the discovery of a second comet, Hyakutake reported his discovery to the National Astronomical Observatory of Japan. This comet was later confirmed by independent observation later that day and dubbed Comet Hyakutake.
At the time of the comet’s discovery, Hyakutake’s magnitude, or brightness, was measured at 11.0 and the comet’s coma, or nebulous envelope around the nucleus of the comet, was measured at 2.5 arc minutes across. It was located 2.0 AU from the Sun. After the discovery, it was noted that the comet could be seen in photographs taken earlier when the comet was 2.4 AU from the Sun. Scientists noted that as Hyakutake passed near the Sun, it did not have a significant fading effect that is common to new comets as the layers of highly volatile materials evaporate due to the presence of the Sun. This led researchers to believe that this was not the comet’s maiden voyage through the solar system and perhaps the comet might yield a great show to those on Earth because more mature comets have a tendency to brighten instead of fade due to the lack of evaporation.
With the anticipation of Great Comet Hale-Bopp, Hyakutake was in danger of fading into obscurity, but the comet would have its day. Three days to be exact. The comet became visible to the naked in early March of 1996 and attained its full brightness on March 25, 1996. At its peak, observation estimated the comets magnitude at 0 and tail lengths of up to 80 degrees were reported as the comet passed within 0.1 AU of the Earth. Due to the small window of Hyakutake’s peak magnitude, it was unable to set the imaginations of humanity of fire as Hale-Bopp did the following year. However, the comet was greatly noted and admired.
Chemical analysis of the comet revealed that it was made primarily of ethane and methane. This was the first time that either of these gases had been detected in a comet. This led researchers to the conclusion that the comet was formed in interstellar space away from the Sun which would have evaporated the volatile gases. Spectrographic analysis of the comet’s ices determined the amount of deuterium, a stable isotope of hydrogen found abundantly in the oceans of Earth, present within the comet to be twice of what is found in Earth’s oceans. This study led to the possible debunking of the theory of Earth’s oceans being caused by cometary collision due the difference in deuterium levels. This finding was further confirmed by the analysis of Hale-Bopp and Halley’s Comet. The most surprising data garnered from Hyakutake’s passage was the revelation that the comet was emitting x-rays. This was the first observation of this phenomenon, but it was later confirmed by separate research that nearly every comet observed exhibited the same behavior. This phenomenon is thought to be caused by interactions between energetic solar wind particles and cometary material evaporating from the nucleus.
Comet Hyakutake’s Nucleus
Great Comet Hyakutake highlighted 1996 with an amazing celestial display, but not only was the show that the comet put on spectacular, but the new information regarding the make-up and emission properties of comets was just as spectacular to those within the scientific community. Although Hyakutake’s bright life span was short, it will continue to be one of the most celebrated cometary events of the last century and the data garnered from the study of this comet will continue to influence cometary research until such earthbound research is no longer necessary.