Geoscience Reference
In-Depth Information
As cross-section area of Karin increases (Karin being brighter), matured
redder surface is replaced by immature fresh surface. The light-curve of
Karin has double peaks of magnitude (where phase are around 0.2 and 0.7,
respectively), and the magnitude at 0.2 is larger than that at 0.7, which
could imply that the surface around 0.2 is mature and darkened by space
weathering while the surface around 0.7 is fresh, although shape difference
might be more responsible for this peak height difference.
Let us reflect the spectral change of Karin according to rotational phase.
Around rotational phase of 0.35, which is the boundary between the first
set and the second set, rapid shift in the degree of space weathering is
observed. As cross-section area of Karin increases (Karin being brighter),
matured redder surface is replaced by immature fresh surface. More red-
dened spectra could be observed at phase earlier than 0.3, and the spectrum
of our first set of Karin could be an averaged data of un-reddened spectrum
and much more reddened spectrum. Actually, visible observations of Karin
also suggested that the surface at earlier rotational phase (
<
0.5) is weath-
ered compared with that at latter phases (
>
0.5).
13
They also showed the
surface at rotational pahse of 0.2 can be most matured (dark and red).
Their results are consistent with our observation.
5. Planning for Re-observation
What is very puzzling in our results is that the major spectral change occurs
between sets of averaging only 50 min apart, which represents only about
15
◦
of rotation of the asteroid. We verified that the standard star's spectra
were not changed before the first set and after the second set of Karin
observation, i.e., we would remove the possibility that the spectral change
was caused by an instrumental or atmospheric effect through the first and
second sets of Karin observation.
12
One hypothesis to explain the observed
rapid spectral change is that Karin is one of cone-shaped fragment at low-
velocity impact forming the Karin family,
12
however, the problem is still
unsolved. It is necessary to perform spectral observation seamlessly in full
rotational phase.
Actually, we have conducted a multispectral Karin observation using
the 1 m Schmidt telescope at the Kiso observatory on January 14-18, 2005
to get the spectral data in full rotational phase. But, unfortunately, the
weather was so bad through the observation that we cannot get a meaning-
ful data. Now, we are planning for re-observation of the asteroid on the next
year. This will be the proof that the variation is intrinsic to the rotation of
