[meteorite-list] What Happened to Comet ISON?

[Ron Baalke]

http://science.nasa.gov/science-news/science-at-nasa/2013/04dec_isonrecap/

What Happened to Comet ISON?
NASA Science News
December 4, 2013

Astronomers have long known that some comets like it hot.  Several of 
the greatest comets in history have flown close to the sun, puffing themselves 
up with solar heat, before they became naked-eye wonders in the night 
sky.

Some comets like it hot, but Comet ISON was not one of them.

The much-anticipated flyby of the sun by Comet ISON on Thanksgiving Day 
2013 is over, and instead of becoming a Great Comet...

"Comet ISON fell apart," reports Karl Battams of NASA's Comet ISON Observing 
Campaign. "The fading remains are now invisible to the human eye."

At first glance this might seem like a negative result, but Battams says 
"rather than mourn what we have lost, we should perhaps rejoice in what 
we have gained - some of the finest data in the history of cometary astronomy."


On the morning of Nov. 28th, expectations were high as ISON neared perihelion, 
or closest approach to the sun. The icy comet already had a riotous tail 
20 times wider than the full Moon and a head bright enough to see in the 
pre-dawn eye with the unaided eye. A dose of solar heat could transform 
this good comet into a great one.

During the flyby, more than 32,000 people joined Battams and other solar 
scientists on a Google+ Hangout. Together they watched live images from 
a fleet of solar observatories including the twin STEREO probes, the Solar 
Dynamics Observatory, and SOHO. As Comet ISON approached the sun it brightened 
and faded again.

"That might have been the disintegration event," says Matthew Knight of 
NASA's Comet ISON Observing Campaign.


Cameras onboard the Solar Dynamics Observatory followed the comet all 
the way down to perihelion and saw ... nothing. 

"We weren't sure what was happening," recalls Knight.  "It was such a 
roller coaster of emotions."

The researchers were surprised again when a fan-shaped cloud emerged from 
the sun's atmosphere. No one knows for sure what was inside. Possibilities 
include a remnant nucleus, too small for SDO to detect, or a "rubble pile" 
of furiously vaporizing fragments. By the end of the day, Comet ISON was 
nothing but a cloud of dust.

"It's disappointing that we didn't get a spectacular naked eye comet," 
says Knight, "but in other ways I think Comet ISON was a huge success. 
The way people connected with Comet ISON via social media was phenomenal; 
our Comet ISON Observing Campaign website earned well over a million hits; 
and I had trouble downloading images near perihelion because NASA's servers 
were swamped."

"So maybe ISON was the 'Comet of the New Century,'" he says.

Battams agrees:  "The comet may be dead, but the observing campaign was 
incredibly successful." Since its discovery in Sept. 2012, Comet ISON 
has been observed by an armada of spacecraft, studied at wavelengths across 
the electromagnetic spectrum, and photographed by thousands of telescopes 
on Earth.  For months at a time, uninterrupted, someone or some spacecraft 
had eyes on the comet as it fell from beyond the orbit of Jupiter to the 
doorstep of the sun itself. Nothing was missed.

The two astronomers hope that the wealth of data will eventually allow 
them and their colleagues to unravel the mystery of exactly what happened 
to Comet ISON. 

"This has unquestionably been the most extraordinary comet that Matthew 
and I, and likely many others, have ever witnessed," says Battams. "The 
universe is an amazing place and it has just amazed us again."

Credits:
Author: Dr. Tony Phillips 
Production editor: Dr. Tony Phillips 
Credit: Science at NASA