Buzz Blog

Was Comet ISON's Eulogy Premature?

Friday, April 04, 2014
According to a new image, scientists jumped the gun when they announced Comet ISON’s death last December. A recent paper that reveals the first image of Comet ISON in visible light indicates that the comet remained intact shortly after its signals in the extreme-ultraviolet ceased upon approaching perihelion on November 28.

The dark center is the portion of the sun, which the scientists blocked. The second inner ring is the visible image the team took and the outer portion of the image is a different image taken by the LASCO/C2 satellite. Notice the band of light that extends from the outer image to the middle image that is a continuation of Comet ISON as it passes perihelion. Credit: Miloslav Druckmuller

“We took the image after the comet had gotten to its closest approach point to the Sun,” said Shadia Rifai Habbal at the University of Hawaii and an author of the paper, which appeared in The Astrophysical Journal Letters this month. “We took the image at 19:12 UT” -- 27 minutes after the comet reached perihelion, when reports had announced it as good as gone.

The image is proof that the comet survived its perihelion passage, the international team reported, albeit for a short period. At the time that Comet ISON was approaching the Sun, Habbal and her colleagues were patiently waiting in Hawaii.


White whisps of the corona are visible
during a 1999 solar eclipse.
Credit: Luc Viatour
On the summit of Haleakala, which is located on Maui island, the scientists used a coronagraph so they could take images in the visible part of the spectrum at the time the comet approached the Sun. A coronagraph blocks light from a star and is a handy tool for imaging objects near the sun and also the Sun’s whispy outmost layer, called the corona. The moon acts as a natural, temporary coronagraph during a solar eclipse, as shown in the image on the right.

By attaching a coronagraph to a telescope at the Mees Solar Observatory, the team shot their images, one of which happened to show the comet intact after it had reached perihelion.

“The problem was … to be absolutely sure what we observed was really the comet,” said Miloslav Druckmuller, lead author of the paper and scientist at Brno University of Technology in Czech Republic. “We must have some reliable proof that the fuzzy band of light we were able to detect is really a comet.”

Druckmüller ultimately determined that their image aligned with another image taken by one of the satellites of the Large Angle Spectrometric Coronagraph (LASCO/C2) to within more than 99.999 percent accuracy, meaning the images are pretty much a guaranteed match.

“It practically excludes random alignment of the two images,” he said.

This might be the only visible light image in existence of Comet ISON during its perihelion passage, the team reports.

Their results do not suggest that Comet ISON ultimately survived its close encounter with the Sun. Scientists captured images of the comet’s remains hours after perihelion, which suggested that most, if not all, of it had disintegrated.

             

Some argue that if the comet had remained intact after perihelion, it would have been a spectacularly bright site for weeks for observers in the northern hemisphere.

Habbal is an expert in solar physics, not comets. In fact, Comet ISON was the first comet she had ever photographed. She was more interested in studying the debris in the comet’s tail than deducing how long the comet remained intact.

The surface of the Sun is hot, but its corona is about 500 times hotter. The corona being the most distant layer and also the hottest of the Sun’s outer layers is a counterintuitive phenomenon that continues to elude explanation.

When a comet barrels through space, it encounters the solar wind – a stream of charged particles. These particles rip electrons from the molecules that comprise the comet, leaving their trace behind in the form of a tail. This is why the tail of a comet is always facing away from the Sun.

These ions, particularly iron ions, are what Habbal and the team are interested in.

“If you can find how many of those elements of iron at different stages of ionization it can tell you something about the processes that heat the corona,” she said.
Posted by Newtonator