Comet watchers had hoped ISON would survive its encounter with the sun's heat, gravity and radiation and be visible to the naked eye as it moved away from the sun through December.
NASA telescopes tracking the comet plunging into the sun's corona saw no evidence of it emerging on the other side, USA Today reported Thursday.
Scientists said they would continue to analyze imagery from the telescopes for signs of the comet or debris from it breaking up.
"At this point, I do suspect that the comet has broken up and died," Karl Battams, a comet scientist for the Naval Research Laboratory, said from the Kitt Peak Observatory in Arizona.
Comet ISON was likely nudged from its home in the distant Oort Cloud by gravity from other stars into its 5 million-year dive toward the sun, astronomers said.
Other comets from the Oort Cloud have been tracked before, but ISON was the first from so far away to pass so close to the sun, at a distance of about 1 million miles.
"This is a spectacularly rare event," Battams said. "We have no idea when we're going to see something this amazing again."
Even if comet ISON has in fact evaporated and broken apart, its behavior during its plunge into the sun will yield new information about both comets and the sun, astronomers said.