Sunday, February 24, 2008

Did Holmes undergo a second - if minute - outburst after all?

Already on day one of comet 17P/Holmes' dramatic outburst back in October 2007 attention was drawn to the fact, that its last outburst in 1892 had been followed by another sharp rise in overall brightness. Would that pattern repeat? After all, eruptions coming in pairs seem to be almost a defining feature of these mysterious outbursts! Nothing at all, however, was reported by visual observers in the four months that today have passed since Holmes' 2007 eruption. But now M. Kidger (in The Astronomer 44 #526 [Feb. 2008] 266) draws attention to a brightening of the comet's inner coma by 0.5 mag. between 2008 Jan. 20 and 21 - recorded by four observers - when it also "took on a much more stellar appearance" and the "radial brightness of the coma became suddenly steeper." The lowest of the light curves here shows what Kidger means. Over the following 10 days the coma faded steadily, and then there was another, smaller event on Jan. 31.

In other news there's a brief report on how it felt to shoot at a satellite, with the statement that in "the next three to four hours" following the hit of USA 193, "a lot of it was burning up as it was coming down" - but neither here nor anywhere else have we heard so far how much mass in how many fragments is still left in orbit. No individual numbers have been assigned to any debris, though there was another sighting of a possible larger fragment. Also, yet more images of the lunar eclipse have appeared, showing e.g. the changing umbra pattern during totality, everything at once or the eclipsed moon in detail. And here is what the wire services would sell you.

1 comment:

Richard Miles said...


The clearest lightcurve is shown at the top of:

If you look carefully there might have been two outbursts, the first one around December 7 is not very distinct, the second on January 21 showed more of a step change.
My hypothesis (based on an outburst mechanism which I have already proposed) is that these periods of increased activity are associated with a very slow rotation rate: current data suggestive of an approx. 40-45 day rotation period of the nucleus. These are not outbursts per se but rather a period of enhanced activity corresponding to the site of the original break-away of material being exposed to full sunlight.

Richard Miles