I have received many questions as to whether these two objects may collide, or whether they might come so close to one another that they can change their orbits to head directly for Earth. Categorically – NO. Minimum distance between the two objects will happen September 13 (three days after the comet passes perihelion), and that distance is 0.1688 a.u., on the order of 25,252,000 km – 10 million km less than the distance of closest approach of Comet Elenin to our planet, which will take place October 16.
As you know, May 21 was the closest approach of Comet C/2010 X1 to asteroid 1999 RQ176; the objects passed all of 225,830 km from each other, more than 100 times closer than the minimum distance between Comet Elenin and asteroid 2005 YU55! After that encounter, new position measuments of the comet and asteroid 1999 RQ176 were obtained. On such a short timescale no influence was noted, which means it is practically nil. For that reason, we can absolutely precisely say that Comet Elenin and asteroid 2005 YU55 will pass by one another and it will not even be noticeable!
Comet Elenin is attracting more and more interest in the scientific community; at the end of July observations were made on the largest submillimeter telescope in the world JCMT. Since August 1st, observations are ongoing with the space telescope STEREO-B; they will continue for several weeks. It is probable that the comet will be visible in the field of the COR2 (STEREO) coronagraph beginning August 20. Beginning September 23rd, for 6 days, the comet will be visible in the field of view of the LASCO C3 coronagraph on the SOHO spacecraft.
Very recently I received information that several more spacecraft may observe comet C/2010 X1 (Elenin), specifically Venus Express and Messenger. These observations will allow us to obtain unique information about the comet at the time of its perihelion when it will not be observable from the Earth.
Observations are planned with SPICAV UV in the 110-310 nm wavelength band on the Venus Express spacecraft and Messenger’s MASCS spectrograph. Moreover, by simultaneous observations from two spacecraft with different points of view, with the VMC camera on Venus Express and the MDIS camera on Messenger, it is possible to obtain a three-dimensional model of the comet’s coma! It is possible that comet C/2010 X1 (Elenin) may become the brightest comet that these two spacecraft may observe during their entire time of service. I hope this application is approved and the observations take place.
M. Drahus, University of California at Los Angeles; Bin Yang, University of Hawaii; and J. Hoge, Joint Astronomy Centre, report the detection of HCN (Hydrogen cyanide) in comet C/2010 X1 on July 30 when at heliocentric distance r = 1.07 AU. Observations between July 30.153 and 30.249 UT at the James Clerk Maxwell Telescope show the J = 4-3 line with area about 0.1 K km/s in antenna temperature scale. Assuming an isotropic production of gas at velocity 0.5 km/s and a Boltzmann distribution of energy levels at 50 K, the derived HCN production rate is 1.5 x 1025 molecules/s, comparable to the mean level measured in comet 103P/Hartley at the same heliocentric distance in late 2010 (Drahus et al. 2011, Ap.J. 734, L4).
http://www.cbat.eps.harvard.edu/iau/cbet/002700/CBET002781.txt (subscription required).