Astronomers believe that Comet ISON could be heading towards a brutal solar storm this Thanksgiving, on Thursday Nov. 28. During this time, ISON is expected to fly just a few million kilometers above the surface of the sun.
Comet Encke and the 2007 CME
Back in 2007, Comet Encke was battered by a powerful solar storm, with observations gathered by NASA’s Solar Terrestrial Relations Observatory (STEREO) spacecraft showing a coronal mass ejection (CME) event transiently ripping off its tail; later, the tail rematerialized, as the comet continuously released streams of dust and gas.
Comet Encke demonstrates the shortest orbital period around the sun of any known comet, and was discovered in Pierre Méchain in 1786.
Meanwhile, the same fate could befall Comet ISON, as it hurtles towards the sun’s grueling atmosphere. It is also of note that, during the upcoming solar storm, ISON will be around 30 times closer to the Sun than Comet Encke was during 2007.
Angelos Vourlidas of the Naval Research Laboratory, and member of NASA’s Comet ISON Observing Campaign (CIOC), talked about the differences between the two events:
“… the year 2007 was near solar minimum. Solar activity was low. Now, however, we are near the peak of the solar cycle and eruptions are more frequent.”
However, as with Comet Encke, ISON is unlikely to be placed in jeopardy during the CME. Karl Battams, astronomer at the Naval Research Laboratory, hopes the brutal solar storm will come to fruition, as it will provide astronomers with a unique opportunity to investigate the influence of extreme conditions on the comet’s tail.
How Will the CME Affect Comet ISON?
Coronal mass ejections are enormous bursts of magnetized plasma clouds, hurled into space by the explosions of sunspots, and typically span millions of miles. Although the precise reason for CME events is not fully understood, recent research suggests that it may be caused by a process called magnetic reconnection, occurring when two oppositely directed magnetic fields are brought together; this process is subsequently accompanied by a massive explosion, releasing massive amounts of matter and electromagnetic radiation into space.
Comet ISON will pass over the sun’s equator on Thanksgiving, around a recent cluster of sunspots – a region that has one of the highest probabilities of CME emission.
The gases inside a CME are not very dense, so the impact is unlikely to inflict any serious damage to the comet. However, its tail is extremely fragile and, as evidenced by Comet Encke’s 2007 solar passage, remains vulnerable to these volatile interactions. Vourlidas elaborates on the exact mechanism by which Encke originally lost its tail:
“The CME that ran over Comet Encke back in 2007 was slow, barely creating a pressure pulse by compressing the solar wind ahead of it… It was this compression which caused the Encke’s tail to fly off.”
Since ISON will be closer to the sun, he goes on to explain how the comet is likely to endure a much faster CME, consequently pummelling it with a shock wave with a stronger magnetic field. Vourlidas confesses that astronomers are simply unable to predict what might happen.
The NASA STEREO-A spacecraft’s HI-1 camera recently recorded both Comet ISON and Comet Encke plunging towards the sun, as the solar winds cause their tails to rhythmically wag, back and forth. The imagery was acquired between Nov. 20 and Nov. 22, 2013.
During a press release, NASA explains the benefit of two comets experiencing a CME at the same moment in time. The space agency explains that the comets would serve as “solar probes,” sampling the storm at two entirely separate locations; this could provide astronomers with unique insight into the 3-dimensional structure of the CME.
NASA officials await Nov. 28 with great anticipation, as Comet ISON potentially squares up against the brutal solar storms of our sun.
By James Fenner