What you're seeing are compression artifacts, highly magnified. We have to
compress the images digitally in order to keep a good rate of taking them and still
be able to telemeter them back (across an increasing distance, which weakens the
signal and limits how much data we can send per unit time) to earth. The images
you are looking at in the video are "space weather beacon mode" images that are
telemetered down nearly continuously:
http://stereo-ssc.nascom.nasa.gov/beacon/beacon_coverage.shtmlin near-realtime, and are both binned (undersampled spatially, down to 512 x 512
pixels) and heavily, lossily compressed digitally onboard (analogous to the various
JPEG compression settings on a digital camera, but much more severe). Then
they're made available on the Website in a variety of magnifications or "upresings"
which only magnify the artifacts. Usually, by now (that is, three days or more after
the data were obtained), we'd have the full-resolution (2048 x 2048 pixel) images,
which are much less heavily, but still lossily, compressed, and are played back to
a Deep Space Network (DSN) ground station via the high-gain antenna on one of
the STEREO spacecraft. Unfortunately, a piece of ground hardware at DSN failed,
and we're only now catching up on the full-resolution data from January 18 onward
--- except the lower-resolution (512 x 512) beacon mode data. People first started
seeing the odd images around that date, when there was a moderate solar
energetic particle event, but those up-resed images have now been replaced on
the SSC Website with the full resolution ones. DSN has caught us up to January
20, the last time I checked.
The compression artifacts are particularly obvious when a particle (cosmic ray or
solar energetic, charged particle) hits the CCD detector on the spacecraft
head-on. (Grazing hits show up as bright streaks.) The compression scheme has
a hard time mathematically representing sharp, single- or few-pixel features, and
you get a characteristic pattern of a bright dot in the middle of a compression
block (a subsection of the image) surrounded by a pattern of dark dots.
Best,
Joe Gurman
(Dr.) Joseph B. Gurman
STEREO Project Scientist