What's Going On? (September 17, 2003)
Hi-res TIF image (4.3M)
Our SOHO team has received a number of questions about this image
taken by the LASCO C3 coronagraph on 12 September 2003. What are all
those swirling lines? Since the launch of SOHO in December, 1995,
we've seen something similar about a dozen times. The images taken
24 minutes before and 30 minutes after this image show nothing
unusual. As in each previous case, it appears that some of SOHO's
multi-layer thermal insulation (MLI), which has become brittle after
almost eight years' exposure to solar radiation, has flaked off and
is passing in front of the wide-angle view of the coronagraph. The
streaking in this 19-second-long exposure is similar to what you
would capture if you were to hold a camera lens open for several
seconds and take a picture of snow falling. Just as the snowflakes
that passed closest to the lens would appear as fat, out of focus
streaks, some of the MLI flakes also appear as thick, bright streaks. |
Why did the MLI flake off? Most likely, a micrometeorite struck the insulation, not an uncommon event for spacecraft. This type of image has usually been observed when a cover of one of the instrument covers has closed with some force and knocked off some of the spacecraft's insulation, but no covers were closing on this occasion.
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