Explanation:
Outstanding in
planet Earth's sky early this year,
Comet McNaught
is captured in this view
from the STEREO A spacecraft.
McNaught's
coma is so
bright, it
blooms into the
long horizontal stripe at the bottom of the field.
Brilliant Venus, near the top left corner, also produces a severe
horizontal blemish in the digital image.
But the sensitive camera does accurately record the
striations in McNaught's
famous dust tail along a region
stretching over 30 million kilometers toward the top right of
the field of view.
A separate, fainter, arching tail just to the left of the
dust tail was initially thought to be an example of a
common ion tail,
formed by electrically
charged atoms
carried away from the comet by
the solar wind.
However,
detailed
modeling indicates that tail is actually due to
neutral iron atoms pushed out by the pressure
of sunlight --
the first ever detected neutral iron tail from a comet.
The iron atoms are thought to originate in
dust grains
from the comet nucleus
that contain the iron-sulfur mineral
troilite (FeS).
