After astronomers worried that Comet ISON had dimmed, they now say the comet is on track for its close approach to the sun at 1:37 p.m. Eastern time on Thursday, passing about 730,000 miles above the sun’s surface.
At that distance, the comet will actually be within the sun’s atmosphere, or corona.
When we reported in recent days on ISON’s approach, some astronomers said they thought it might have fallen apart. But then the comet brightened up again. On Wednesday afternoon, Karl Battams, an astrophysicist at the Naval Research Laboratory, reported that ISON was still “a very healthy sungrazing comet!â€
Dr. Battams and other astronomers are at the Kitt Peak National Observatory in Arizona observing ISON. NASA’s sun-watching spacecraft are also taking close note of the comet, which spent most of the last 4.5 billion years in the farthest reaches of the solar system.
Because ISON appears to be a pristine relic of the very beginnings of the solar system, scientists hope to glean clues on how the bits of dust and ice came together to form planets.
Will ISON survive its close encounter? “Unfortunately,†Dr. Battams wrote, “the answer is not particularly satisfying: we will not know if ISON will survive until it actually does so, or gets vaporized before our very eyes!â€
Regardless of what happens, there is no chance that ISON could pose any danger to Earth, Dr. Battams said.
Even if it dies, the comet could still give off an impressive light show.
Last year, another sungrazing comet, named Lovejoy, appeared to have survived its passage through the corona, but it later became apparent that its nucleus had disintegrated. Nonetheless, its remnants provided a spectacular night sky for people in the Southern Hemisphere. This time, it will be people in the Northern Hemisphere who may get the good view of the comet show.
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