Geoscience Reference
In-Depth Information
September
2003
Karin
Earth
September
2004
Sun
Fig. 4. A rough schematic illustration of the orbital configuration of (832) Karin and
the Earth in September 2003 and September 2004. Relative location of the two bodies
is determined by the solar phase angle in Table 2. The Earth was roughly at the same
position at our 2003 and 2004 observations. We assume that rotation axis of this (maybe)
cone-shaped asteroid is almost parallel to its orbital plane, and it has a small portion of
red surface (dark gray area).
The existence of the color variations found in our 2003 observation is
supported by a near-infrared spectroscopic observation of this asteroid that
was performed at nearly the same time as our observation. Sasaki
et al.
16
deployed the Cooled Infrared Spectrograph and Camera for OH-airglow
Suppressor (CISCO) at the 8.2-m Subaru telescope on MaunaKea, Hawaii,
and observed (832) Karin in near-infrared wavelength on September 14,
2003, close to the date of our 2003 observation. As a result, Sasaki
et al.
16
obtained the near-infrared spectra of this asteroid at three different rota-
tional phases; 0.30-0.33, 0.34-0.38 and 0.45-0.51 in our Fig. 3(a). They
found a significant difference in the slope between the spectrum obtained
at phase = 0
.
30-0.33 and the others. The former is similar to the spectra of
ordinary S-type asteroids (i.e., “red” spectrum), while the latter two match
well with the spectra of ordinary chondrites. Sasaki
et al.
16
interpreted this
asteroid's spectrum difference as being due to the mixed distribution of
matured and fresh surfaces. This trend of color variation is quite similar to
what we obtained in our 2003 observation (Figs. 3(b) and (c)).
A small inconsistency between our and Sasaki's observations is the dif-
ference in the rotation phase where the “red” spectrum was observed: In
our 2003 result, the surface of (832) Karin seemed mature when the rota-
tion phase was
0.2, while Sasaki's result claims that the mature sur-
face appeared when the phase was around 0.3. We think this mismatch
was caused by an uncertainty in rotational period determination, and
does not have a significant influence on our assertion that this asteroid
∼
