X-type asteroid
The
X-group of
asteroids collects together several types with similar spectra, but probably quite different compositions.
Tholen classification
In the
Tholen classification the
X-group contains the types:
*
E-type*
M-type, the largest grouping
*
P-typeSince in this scheme the
albedo is crucial in discriminating between the above types, some objects for which
albedo information was not available were assigned an
X-type. An example of this is
50 Virginia.
SMASS classification
The
SMASS classificationdoes not use
albedo, but several spectral types are distinguished on the basis of
spectral features which were too subtle to be visible in the broad-band ECAS survey used for the
Tholen scheme. The
X-group contains the types:
*core
X-type containing the asteroids with the most "typical" spectra
*Xe-type of asteroids whose spectra contain a moderately broad absorption band around 0.49 μm. It has been suggested that this indicates the presence of
triolite (FeS). There is some correlation between this group and the Tholen
E-type.
*Xc- and Xk-type asteroids, which contain a broad convex
spectral feature in the range 0.55 μm to &0.8 μm (i.e. increased
flux#electromagnetic_radiation in this range). These
spectra tend to be intermediate between the core
X-type and the
C and
K-type. Apart from the Xe-type, there is no significant correlation between the split into these SMASS types and the Tholen
E,
M, and
P-types. All the types in the
X-group contain a mixture of asteroids classified as either type
E,
M, or
P.
*
Asteroid spectral types*
L-type asteroid*
S-type asteroid*
K-type asteroid#
S. J. Bus and R. P. Binzel Phase II of the Small Main-belt Asteroid Spectroscopy Survey: A feature-based taxonomy, Icarus, Vol. 158, pp. 146 (2002).
