At least part of comet ISON likely survived the comet's graze past the sun Thursday, a new scientific analysis shows, despite initial widespread agreement that the comet had likely been fried to bits.
"Late-night analysis from scientists with NASA's Comet ISON Observing Campaign suggest that there is at least a small nucleus intact," NASA reported in a news release Friday morning, adding that the latest news was "continuing a history of surprising behaviour" for the comet.
The nucleus is the loosely packed ball of frozen gas, rock and dust that makes up the core of a comet. As a comet moves close to the sun, that material vapourizes and spews from the surface, creating a bright "coma" or atmosphere that can expand into a long tail.
On Thursday, numerous solar observatories were pointed at ISON as it passed within 1.6 million kilometres of the sun at 1:37 p.m. ET.
In the four hours afterward, it could not be seen on the other side of the sun by either NASA's Solar Dynamics Observatory spacecraft or by ground-based solar observatories, leading may scientists to suggest that the comet had likely been destroyed by the sun's heat during its close encounter.
The European Space Agency (ESA) officially declared the comet dead on Twitter.
However, a bright streak of material was seen on the other side of the sun in images captured by the ESA and NASA's Solar and Heliospheric Observatory "later in the evening," NASA reported.
Initially, NASA solar physicist Alex Young told The Associated Press that the streak was most likely just a trail of dust.
However, instead of fading, that trail appeared to get brighter Friday, suggesting "at least some small fraction of ISON has remained in one piece," U.S. navy solar researcher Karl Battams wrote on his blog.
The ESA also backtracked on its declaration, tweeting Friday morning, "Well well, it seems reports of comet #ison's demise have been greatly exaggerated!"
ESA comet expert Gerhard Schwehm later tweeted that from his initial look at the SOHO images, the comet's nucleus has "mostly disintegrated," but more analysis was needed.
Battams also cautioned on his blog that even if a solid nucleus remained, it might not survive for long.
Researchers were still not sure why many solar observatories were unable to see the comet after its close encounter with the sun.
A post on the website of ESA's Proba 2 satellite Friday suggested it was possible that ISON:
- Didn't release enough material to be visible because it wasn't close enough to the sun to cause enough heat and evaporation.
- Wasn't made up of the right ingredients – for example, it didn't contain enough iron – to glow in the colours that the Proba 2 satellite could see.
Comet ISON is unique and has been of great scientific interest because it is the first sun-grazing comet ever observed from the Oort Cloud, a vast region of comets and debris near the edge of the solar system, far beyond the outermost planets. It is also one of the largest sun-grazing comets ever observed.