from the GhoSST
2 database is shown in Fig. 2.40 and compared to the CO 2 ice
absorption coefficient which has considerably more fine structure in the near-IR.
The exact positions of the features are dependent upon the exact conditions in
which the ice finds itself. Temperature dependence was shown by Grundy and
Schmitt (1998) after laboratory studies had shown in the early 1980s that the infrared
features display temperature effects in band shape and position. Ehrenfreund et al.
(1996) showed that the infrared features of H 2 O ice when contained within matrices
of other molecules were also modified and presented a “fingerprint” of the matrix.
Mastrapa et al. (2008) also analysed the differences between amorphous and crystalline H 2 O ice spectra and identified weakening of bands and shifting of those bands
to shorter wavelength in amorphous H 2 O ice spectra.
Following Grundy and Schmitt (1998), the strength of a 1.65 μm absorption
feature in crystalline H 2 O ice is now used as a diagnostic for the presence of
crystalline ice over the amorphous form. The presence of crystalline H 2 O on objects
remote from the Sun (surface equilibrium temperatures ≲80 K) is then assumed to
indicate either past closer proximity to the Sun or evidence for internal heating
followed by cryo-volcanism. For example, Jewitt and Luu (2004) examined spectra
of the KBO (50000) Quaoar to conclude the latter. Terai et al. (2016) also detected
crystalline ice on (136108) Haumea and (90482) Orcus but also on (42355) Typhon
and 2008 AP 129 , both of which are smaller than the minimum size for inducing cryovolcanism (and therefore amorphous to crystalline phase transition) through thermal
evolution resulting from the decay of long-lived isotopes.
Furthermore, activity was detected in the long period comet C/2017 K2
(PANSTARRS) at >23 AU by Jewitt et al. (2017), who argued that this could not
be explained by the amorphous-crystalline transition. Nucleus temperatures at 23 AU
are too low (60–70 K) either for water ice to sublimate or for amorphous ice to
crystallize, requiring another source for the observed activity (Jewitt et al. 2017).
Fig. 2.40 Near-infrared
absorption coefficients of
H 2 O ice (dashed line) and
CO 2 ice (solid)
2 https://www.sshade.eu/db/ghosst
106
2 The Nucleus
2 database is shown in Fig. 2.40 and compared to the CO 2 ice
absorption coefficient which has considerably more fine structure in the near-IR.
The exact positions of the features are dependent upon the exact conditions in
which the ice finds itself. Temperature dependence was shown by Grundy and
Schmitt (1998) after laboratory studies had shown in the early 1980s that the infrared
features display temperature effects in band shape and position. Ehrenfreund et al.
(1996) showed that the infrared features of H 2 O ice when contained within matrices
of other molecules were also modified and presented a “fingerprint” of the matrix.
Mastrapa et al. (2008) also analysed the differences between amorphous and crystalline H 2 O ice spectra and identified weakening of bands and shifting of those bands
to shorter wavelength in amorphous H 2 O ice spectra.
Following Grundy and Schmitt (1998), the strength of a 1.65 μm absorption
feature in crystalline H 2 O ice is now used as a diagnostic for the presence of
crystalline ice over the amorphous form. The presence of crystalline H 2 O on objects
remote from the Sun (surface equilibrium temperatures ≲80 K) is then assumed to
indicate either past closer proximity to the Sun or evidence for internal heating
followed by cryo-volcanism. For example, Jewitt and Luu (2004) examined spectra
of the KBO (50000) Quaoar to conclude the latter. Terai et al. (2016) also detected
crystalline ice on (136108) Haumea and (90482) Orcus but also on (42355) Typhon
and 2008 AP 129 , both of which are smaller than the minimum size for inducing cryovolcanism (and therefore amorphous to crystalline phase transition) through thermal
evolution resulting from the decay of long-lived isotopes.
Furthermore, activity was detected in the long period comet C/2017 K2
(PANSTARRS) at >23 AU by Jewitt et al. (2017), who argued that this could not
be explained by the amorphous-crystalline transition. Nucleus temperatures at 23 AU
are too low (60–70 K) either for water ice to sublimate or for amorphous ice to
crystallize, requiring another source for the observed activity (Jewitt et al. 2017).
Fig. 2.40 Near-infrared
absorption coefficients of
H 2 O ice (dashed line) and
CO 2 ice (solid)
2 https://www.sshade.eu/db/ghosst
106
2 The Nucleus