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In this frame grab taken from enhanced video made by NASA’s STEREO-A spacecraft, comet ISON, left, approaches the sun on Nov. 25, 2013.The Associated Press

Comet ISON is no more.

In the lead-up to its dramatic encounter with the sun on Thursday, the ill-fated celestial traveller first dimmed and then disappeared. Soon after, scientists staffing a flotilla of satellites that were monitoring the event reported there was nothing left to observe.

"We haven't seen anything," said Dean Pesnell, a project scientist with NASA's Solar Dynamics Observatory (SDO), "and we're hearing from our science community that the comet is not really showing up."

The news comes as a disappointment, if not a total surprise to skywatchers who have been eagerly following ISON's progress since it was discovered last year by a pair of Russian astronomers working with the International Scientific Optical Network, after which the comet is named. Until Thursday, hopes were running high that the comet would survive its scorching hairpin turn around the sun and possibly go on to become the most spectacular comet seen so far this century.

However, as ISON hurtled ever closer to its destiny, scientists speculated that the nucleus of the comet – a chunk of ice and dust not more than two kilometres across – might disintegrate while passing within 1.2 million kilometres of the sun's surface, experiencing temperatures of up to 2700 C.

Thousands began tuning in online as the comet neared its closest approach to the sun, known as "perihelion," at 1:44 p.m. ET. But an hour before, after flaring up to a peak brightness greater than the most luminous stars in the night sky, the comet began to fade and its head became less distinct.

"You would expect it to get brighter and brighter but unfortunately it got dimmer and dimmer as it got close to the sun," Dr. Pesnell said.

That seemed ominous to experts watching snapshots streaming from the Solar and Heliospheric Observatory (SOHO), a joint U.S. and European satellite that has witnessed the demise of many so called "sun-grazing" comets.

"Comet ISON is dying before our eyes!" wrote Sky and Telescope senior editor Alan MacRobert on the magazine's websiteof Sky and Telescope magazine, where he is a senior editor.

Karl Battams, an astrophysicist with the U.S. Naval Research Laboratory in Washington, D.C., told viewers during a NASA video that, "If ISON has completely fallen apart it's not good news for ground-based observing."

By 3:36 pm a "headless" stream of comet debris could be seen streaking away from the sun in SOHO images. Although some debris could survive and subsequently fly out of the solar system after the comet's breakup, it is not expected to be visible to observers watching from Earth.

"We have never seen a comet like this," said Dr. Battams.