Astronomers monitoring Comet Elenin have noticed the comet has decreased in brightness the past week, and the coma is now elongating and diffusing. Some astronomers predict the comet will disintegrate and not survive perihelion, its closest approach to the Sun.
On August 19, a massive solar flare and coronal mass ejection hit the comet, which may have been the beginning of the end for the much ballyhooed lump of ice and dirt.
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“We’ve been following it in the STEREO spacecraft images and a number of amateurs have been following it in their telescopes,” said Australian amateur astronomer Ian Musgrave, author of the Astroblog website. “Shortly after the coronal mass ejection the comet flared up and you could see some beautiful details in the tail, with the tail was twisting about in the solar wind. But shortly after that Earth- bound amateurs reported a huge decrease in the intensity of the comet. We think it may presage a falling apart of the comet.”
“It really has been a beautiful little comet and it deserves a better fate than to be overhyped by doom-sayers,” said Musgrave.
Elenin is a long period comet originating from the outer edges of our solar system, and Musgrave noted that comets coming from the Oort cloud which are making their first pass through the solar system tend to be under-performers in terms of brightness. “They don’t brighten as quickly as comets that come around more than once,” he said, “and in looking at the relationship between the brightness and the distance from the Sun, we find empirically that comets that brighten on roughly the same speed as Elenin tend to be likely to fall apart at perihelion.”
However, Musgrave added, each comet is unique. “Some comets will survive and some won’t. The fact that this comet decreased in brightness after the CME, possibly indicates that the comet will not survive. Another possibility is that merely the CME wiped away the coma — the bright cloud of particles around the comet — and the volatiles of the comet might take awhile to come back and recreate the coma, if it does survive.”
Elenin’s mass is smaller than average and its trajectory will take it no closer than 34 million km (21 million miles) of Earth as it circles the Sun. It will make its closest approach to Earth on October 16th, but be closest to the Sun on Sept. 10.
Another Australian amateur Michael Mattiazzo has been taking images of the comet (see his website, Southern Comets) and he has noticed that the nucleus appears to be elongating. When that occurs, usually the comet disintegrates or splits apart. Above is an animation Mattiazzo created from images he took of Comet Elenin on August 19, 22, 23, 27 & 29.
You can see a wide-field view of the comet by astrophotographer Rob Kaufmanns, comparing the view from August 19, 23 and 26 at this link.
A similar process took place just a few weeks ago with another comet, 213P Van Ness.
Do comets break apart often?
“You don’t see it it that often, but it happens surprisingly more than people think,” Musgrave said. “Van Ness just happened, but ever couple of years there is a comet that visibly breaks up into fragments, maybe about 6 comets in the last 10 years — excluding the Kreutz-sun-grazer family of comets which split and vaporize on a regular basis.”
Unfortunately, the likely demise of Comet Elenin hasn’t put a lid on the doomsdayers who have predicted earthquakes or three days of darkness or a collision with Earth.
“The doomsdayers are just saying that more bad things will happen!” laughed Musgrave. “But you have to remember that when a comet breaks up, the fragments stay in the same orbit. If it evaporates, you’ll have a mass of rubble and gas on the same orbit. People don’t seem to get that space is big, really big, and when a comet breaks up it follows Newtons Laws and the fragments will slowly draw apart, but over the timescale that we see them, the difference will be so miniscule.”