A 'Sun-grazing' comet as caught by SOHO's LASCO C2 camera as it dived toward the sun on 5 July and 6 July 2011. SOHO is the overwhelming leader in spotting sungrazers, with over 2000 spotted to date, aided by the fact that the sun's bright light is itself blocked out by a coronograph.
Credit: SOHO (ESA & NASA)
MARYLAND: A comet has caught doing something never seen before: die a scorching death as it flew too close to the Sun.
That the comet met its fate this way was no surprise - but the chance to watch it first-hand amazed even the most seasoned comet watchers, who published their observations in Science today.
"Comets are usually too dim to be seen in the glare of the Sun's light," said Dean Pesnell at NASA's Goddard Space Flight Centre in Maryland, who is the project scientist for NASA's Solar Dynamic Observatory (SDO), which snapped images of the comet. "We've been telling people we'd never see one in SDO data."
But an ultra bright comet, from a group known as the Kreutz comets, overturned all preconceived notions. The comet can clearly be viewed moving in over the right side of the Sun, disappearing 20 minutes later as it evaporates in the searing heat.
Watching a comet death
The movie is more than just a novelty. Watching the comet's death provides a new way to estimate the comet's size and mass. The comet turns out to be somewhere between 45 to 91 m long and have about as much mass as an aircraft carrier.
"Of course, it's doing something very different than what aircraft carriers do," said lead author Karel Schrijver, a solar scientist at Lockheed Martin in California and the principal investigator of the Atmospheric Imaging Assembly instrument on SDO. "It was moving along at almost 400 miles per second (643 km per second) through the intense heat of the Sun - and was literally being evaporated away."
Typically, comet-watchers see the Kreutz group comets only through images taken by coronagraphs, a specialised type of telescope that views the Sun's fainter out atmosphere, or corona, by blocking the direct blinding sunlight with a solid occulting disk.
A breathtaking sight
On average a new member of the Kreutz family is discovered every three days, with some of the larger members being observed for some 48 hours or more before disappearing behind the occulting disk, never to be seen again. Such 'Sun-grazer' comets obviously destruct when they get close to the Sun, but the event had never been witnessed.
The journey to categorising this comet began on 6 July 2011 after Schrijver spotted a bright comet in a coronagraph produced by the SOlar Heliospheric Observatory (SOHO). He looked for it in the SDO images and much to his surprise he found it. Soon a movie of the comet circulated to comet and solar scientists, eventually making a huge splash on the Internet as well.
Karl Battams, a scientist with the Naval Research Laboratory in Washington, who has extensively observed comets with SOHO and co-author on the paper, was skeptical when he first received the movie. "But as soon as I watched it, there was zero doubt," he said. "I am so used to seeing comets simply disappearing in the SOHO images. It was breathtaking to see one truly evaporating in the corona like that."
