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On 24 May a pair of comets arced in tandem towards the Sun, their paths taking them to just 70 000 kilometres above the Sun's surface, deep within the searing multimillion-degree solar atmosphere The tails from the pair of comets survived the close encounter with the Sun, even after the Sun's intense heat and radiation vaporized their heads.
The comets belong to the Kreutz family of sun-grazing comets, often seen by the European Space Agency and NASA SOHO spacecraft diving towards the Sun. The pair showed a very unusual trait, what appears to be a faint tail can be seen moving away from the Sun, seemingly emanating from a point in the orbit beyond the comet's closest approach. Normally, sun grazers simply fade and disappear at an earlier stage, obliterated by the Sun's intense heat and radiation pressure.
Another pair of Kreutz sun grazers with such a "headless tail" was observed in June 1998, when the observing geometry was very similar. More than 600 sun grazing comets have been observed by SOHO in the past six years, although this is only the third showing any signs of this behaviour. However, it seems likely that these observations will confirm the existence of such comets.
"Everyone who's seen this agrees it's a very interesting observation," said Dr. Douglas Biesecker, a solar researcher at the National Oceanic and Atmospheric Administration's Space Environment Center in Boulder, Colorado, USA the head of SOHO's comet discovery program. SOHO has become the most prolific comet finder in history.
The tail is most likely the dusty remains of the comet's nucleus, being pushed out by Solar wind after all the ice in the nucleus has evaporated, thus eliminating the processes maintaining a bright coma surrounding the nucleus. Studies of the dust cloud may reveal clues to the size distribution of the dust grains.
Comets are chunks of ice and dust that zoom around the solar system in elongated orbits. Often referred to as "dirty snowball" comets range in size from a large boulder to a large city. As the comet gets close to the Sun, solar heat and light energise gas and dust from the nucleus, forming the coma, an extensive bright cloud around the nucleus. The coma is then pushes back by the solar pressures to form a dust and gas tail, a comet's tails can be millions of kilometres long. Both tails point away from the Sun, even when comets that are travelling back away from the sun out in to the solar system.
More info: SOHO
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