There is an internal gas envelope and so this coma is really rare because it is external. The diameter is approximately 80,000km. http://spaceobs.org/en/2011/04/10/comet-elenin-continues-to-increase-in-size-and-another-close-approach-with-a-large-main-belt-asteroid/
An asteroid (which you will find is related to Comet Elenin in that it will be meeting it's tail) called 2005 YU55 is also approaching earth. This "near earth object" will be approaching its near Earth space in November 2011 (approximately). The size of this asteroid is approximately 1300 ft. in diameter. This asteroid has been designated a "potentially hazardous asteroid" by The Minor Planet Center in Cambridge, Mass.
Both of these objects with potential hazard for Earth are being extensively monitored via radar and infrared observations. While Elenin is being observed extensively because of its growth, long, large tail, and trajectory, with possible changes, 2005 YU55 is being observed because NASA shows that on 11-9-2011 this asteroid will be only .0022 AU from earth. Should we be concerned, given a margin of error?
NASA has been working on emergency preparedness improvement and really pushing family preparedness. The emphasize planning, practicing, and detailing our preparedness plan.
Some say that this is Bible prophecy. There is so much discussion about this. However, we need to prepare in a real physical sense for emergencies of all kinds and not worry about these doomsday theories as much because we cannot control comets and asteroids.
Predictions from various sources are that asteroid 2005 YU55 will hit Comet Elenin's tail when they are closest to Earth or somewhere along the way. Regardless of when this happens, the trajectory for either "near Earth object" may drastically change. I'll leave it to you to decide if that would be good or would be bad for Earth.
Will these two space objects meet and will they affect Earth? All we can do is watch. In any case, this is an even stronger push for everyone to work on their emergency preparedness.
We know there have been massive preparedness exercises throughout the world for some largely impacting disaster. One of the more disturbing preparedness pieces of information I have found is that FEMA has ordered the following...
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