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Wednesday, April 21, 2010


The Case of the Missing Comet (or - where oh where is Catalina)

Left image, predicted position of comet C/2009 O2 Catalina as seen from the STEREO Behind spacecraft on 13 April at 8:49 UT as visualised in Celestia. Right image, an actual image of the same area from the STEREO spacecraft on 13 April at 8:49 UT. Comparison stars (Algedi, Dabih) are indicated in both images, click to embiggen.

For the past few days the stereohunters have been watching the images from the H1 instrument of the STEREO Behind sapcecraft, comet C/2009 O2 Catalina, already faintly visible in H1A images, was going to come within about 0.23au of STEREO B. Orbital predictions (see above left image, from orbits entered into Celestia) suggested the comet would cross the H1B imaging area on April 13 (CometAl's predictions put it further left than mine, to the left of Algedhi, but still within the image frame).

Well, as you can see in the righthand image, which is spectacularly devoid of any comet, this did not come to pass. I checked all the 13th and most of the14th, and nothing appeared. The Stereohunter list was silent. Obviously the comet didn't appear. It was still visible in the H1A camera, faintly, so it hadn't evaporated. What happened?

It simply looks like the earlier orbital elements were out, here is the position of C/2009 O2 Catalina seen from H1B as plotted in SkyMap using the latest orbital elements from JPL HORIZONS (as before the comaprison stars Algedi, Dabih are shown, the black rectangle is the edge of the H1B image frame).

It missed H1B by a country mile.


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