Sat, Nov 30, 2013 page7

• Comet circles sun, but its fate is uncertain

  ASTRONOMERS WAIT: The comet was expected to lose about 3 million tonnes of mass per second as it rounded the sun, but images suggest it may have survived

  • AP and AFP, STOCKHOLM and WASHINGTON
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  Scientists are studying spacecraft images to find out whether a small part of Comet ISON survived its close encounter with the sun.

  The comet at first seemed to have fallen apart as it approached the sun’s surface, but new images yesterday showed a streak of light that some said could indicate it was not game over just yet.

  US Navy solar researcher Karl Battams wrote on his blog that “it does appear that at least some small fraction of ISON has remained in one piece.”

  He said that even if there is a solid nucleus, it may not survive for long.

  The European Space Agency, which had declared ISON’s death on Twitter on Thursday, was backtracking yesterday, saying the comet “continues to surprise.”

  The large block of ice and rock had been expected to skim 1.17 million kilometers above the sun’s surface at about 6:30pm GMT yesterday.

  It was estimated that ISON would undergo temperatures of 2,700oC and lose 3 million tonnes of its mass per second as it made its journey around the sun.

  Most astronomers had predicted that ISON would not survive the trip.

  Several solar observatories watched the comet during its closest approach to the sun, known as its perihelion.

  And the comet became faint while still within view of NASA’s Solar Terrestrial Relations Observatory, and the joint European Space Agency and NASA’s Solar and Heliospheric Observatory. NASA’s Solar Dynamics Observatory, however, could not see the comet.

  “It does seem that comet ISON probably has not survived its journey,” Battams said after looking at space images.

  “I am not seeing anything that emerges from behind the solar disk and that I think could be the nail in the coffin,” he told a roundtable organized by NASA.

  Phil Plait of the Bad Astronomy blog agreed, saying he had a “strong suspicion that ISON may be an ex-comet.”

  Carey Lisse, a senior research scientist at Johns Hopkins Applied Physics Laboratory, compared the comet to a “loose snow ball,” a rather weak and easily broken up with half or a third of its mass coming from water.

  Lisse called the comet a “dinosaur bone” of the solar system’s formation, stressing the key role of comets in building planets.

  ISON was about half the size of an average comet, with an estimated maximum diameter of 1.2km.

  ISON has galvanized astronomers since its discovery by a Russian team in September last year because it traces its origins to the start of the solar system, said to be 4.5 billion years ago.

  It is thought that several million years ago, ISON escaped from the theorized Oort cloud, a grouping of debris halfway between the sun and the next closest star.

  “This is a very dynamic situation. We have never seen a comet like this coming from the Oort cloud and going in the sun grazing orbit,” Battams said.

  “This particular comet is of extreme interest to us,” NASA planetary science director James Green said, adding that it is rare to find comets that come from so far away in the solar system.

  As ISON approached the sun, the fluctuations of its tail showed usually invisible solar wind patterns made of particles constantly ejected by the sun.

  The comet had shown erratic behavior in recent days, shining brighter before suddenly losing its luminous intensity.

  Some astronomers wondered if it was already in the process of disintegrating.
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