Comet ISON dies as it rounds the Sun.


Our star apparently destroyed this surprisingly fragile celestial visitor during their close encounter.
Time-lapse image of Comet ISON from SOHO
Comet ISON comes in from the bottom right and moves out toward the upper right, getting fainter and fainter, in this time-lapse image from the ESA/NASA Solar and Heliospheric Observatory. The image of the sun at the center is from NASA’s Solar Dynamics Observatory.
ESA/NASA/SOHO/SDO/GSFC
Comet ISON (4.5 billion B.C. – A.D. 2013) survived for more than 4.5 billion years in the frigid depths of the solar system, but it fizzled during its brief moment in the Sun on November 28. Through a combination of ISON’s delicate makeup, the Sun’s intense heat, and — most importantly — our star’s powerful tidal forces, the comet’s nucleus failed to survive its brush within 730,000 miles (1.16 million kilometers) of the Sun’s surface.As the comet approached perihelion (its least distance from the Sun) November 28, it continued to brighten at roughly the rate astronomers had predicted. Late on the evening of the 27th (in North America), ISON peaked at magnitude –2.0. Images from coronagraphs aboard both the Solar and Heliospheric Observatory (SOHO) and the Solar Terrestrial Relations Observatory (STEREO) showed the comet as a bright point of light trailed by one distinct dust tail and a narrow dust streamer.

But ISON started to fade even before its closest approach to the Sun. The Solar Dynamics Observatory (SDO), which is equipped with the best cameras for close-up observations of our star and its surroundings, failed to see the comet at perihelion. And once ISON had moved far enough beyond the Sun that it could reappear in SOHO’s coronagraphs, it was nowhere to be found.

As astronomers began to write their post-mortems, however, the unpredictable comet rose from the dead like the legendary Phoenix. Some 24 hours after perihelion, SOHO once again captured images of ISON showing a thin dusty tail and a diffuse central condensation that some interpreted as a small remnant of the comet’s nucleus. But the revival soon began to peter out — by late on November 29, the glow had faded to around 6th magnitude.

It appears that the show amateur astronomers were hoping ISON would produce once it emerged from the Sun’s glare in early December won’t take place. Most scientists think the nucleus has dissipated, and any remaining dust likely will be too faint to see through anything but large telescopes. Even though ISON’s saga seems over, astronomers will spend months poring over their observations of this one-of-a-kind visitor.

 

ISON’s Ghost: ‘Comet of the Century’ is Now Ex-Comet


Sad news, comet fans: ISON is no more. It’s a vaporized husk of its former self. A sublimated dirty snowball. Comet ISON is an ex-comet and this time it’s not playing.

This sad turn of events is brought to you by the joint NASA/ESA Solar and Heliospheric Observatory (SoHO)’s LASCO instrument that gives a wide-angle view of the sun’s atmosphere (pictured above). For the duration of Comet ISON’s close approach to our nearest star, LASCO has been carefully tracking the comet’s progress. After many heart-stopping hours post-perihelion on Nov. 28, space experts nearly gave up hope — ISON had vanished from LASCO’s view, apparently not surviving the sun’s extreme tidal forces and powerful radiation.

But then, just as the U.S. was recovering from Thanksgiving turkey and wine, ISON re-energized; a component of its roasted nucleus had survived the turmoil and was brightening.

Unfortunately, the brightening was short-lived. Despite a couple of days of hope, Comet ISON’s nucleus has all but disappeared, leaving a ghostly wisp of dust behind.

The “Comet of the Century” is now, officially, the Turkey of the Century.

“Among experts, a consensus is building that the comet broke apart shortly before perihelion (closest approach to the sun),” writes Tony Phillips, NASA astronomer and curator of Spaceweather.com.

Like the countless sungrazing comets that have come before it, ISON succumbed to the close solar pass. Although hopes were high that the comet would survive the plunge, no one really knew what ISON was going to do. As a “virgin” comet from the Oort Cloud (a hypothetical cloud of cometary objects approximately one light-year from the sun), this was ISON’s first visit to the inner solar system. With little information on the comet’s composition, cometary fragmentation was always a possibility.

All that remains of Comet ISON seems to be a fan-shaped debris field of small fragments of the once-mighty cometary nucleus, each shard frantically venting the remaining ices into space. Any hope of seeing a dazzling naked-eye comet just in time for Christmas is vaporizing faster than the sublimating ISON fragments that now litter interplanetary space.