616 Encyclopedia of the Solar System
FIGURE 11 Near-infrared reflection spectrum of Quaoar
(black) compared to a spectrum of H 2 O ice (red). The broad
absorption bands near 1.5μm and 2.0μm reveal the presence of
H 2 O ice on the surface of Quaoar. The narrow absorption band
near 1.65μm indicates the presence of crystalline H 2 O ice and is
not present in amorphous ice. (Courtesy of David Jewitt and
Jane Luu)
satellite Trition, which may be a captured KBO, Eris, and
136472 (2005 FY 9 ).
Perhaps one of the most intriguing spectroscopic results
comes from David Jewitt and Jane Luu’s observations of
Quaoar. Specifically, they find not only the H 2 O ice bands
at 1.5 and 2.0μm, but they also find another H 2 O band
at 1.65μm (Figure 11). The later band suggests the sur-
prising result that the H 2 O-ice has a crystalline rather than
an amorphous structure. The H 2 O molecules of crystalline
ice have a periodic structure whereas the H 2 O molecules
of amorphous ice do not. Crystalline H 2 O on Quaoar is a
surprise because Quaoar’s maximum surface temperature
is only∼ 50 ◦K. At such a low temperature, it is difficult
for the H 2 O molecules to arrange themselves into a co-
ordinated structure of a crystal lattice; somewhere around
100 ◦K, amorphous ice arranges itself into an ordered crys-
talline lattice. In other words, the 1.65-μm band suggests
that the H 2 O-ice on Quaoar was somehow heated to tem-
peratures above 100◦K.
An intriguing possibility for the source of the “warm”
H 2 O on Quaoar is NH 3 -H 2 O volcanism. Long ago, long-
lived radioactive elements heated the interior of Quaoar,
and that heat may still be propagating through its inte-
rior. The heat may have been sufficient to create a melt
of H 2 O and NH 3. The lower density melt may have per-
colated upward, perhaps forming fluid-filled cracks all the
way or nearly all the way to the surface in the surrounding,
higher density icy-rock mixture. Eventually, the cooling
“lava” containing crystalline H 2 O ice and crystalline am-
FIGURE 12 Near-infrared spectrum of Quaoar compared to
near-infrared spectra of Pluto and Charon. The spectra of
Quaoar and Charon are similar in that they exhibit three strong
H 2 O-ice absorption bands at 1.5μm, 1.65μm, and 2.0μm, but
no CH 4 -ice bands. The spectrum of Pluto exhibits strong CH 4
ice bands. (Courtesy of David Jewitt and Jane Luu)monium hydrate might become exposed by occasional im-
pacts on Quaoar’s surface. What makes this mechanism
even more intriguing is that Jewitt and Luu claim there
is evidence for an ammonia hydrate band in their spectra
of Quaoar. Ammonia-water volcanism as the source of the
crystalline H 2 O ice is highly speculative. Some other mech-
anism, not requiring a warm interior and volcanoes, may
explain the presence of the crystalline H 2 O ice on Quaoar.
Figure 12 illustrates that Quaoar has a spectrum simi-
lar to Charon, but quite different from Pluto. Quaoar and
Charon exhibit the 1.5- and 2.0-μmH 2 O-ice bands as well
as the 1.65-μm crystalline band, but none of the strong CH 4
ice bands seen on Pluto. Note that Quaoar has the 1.65-μm
band despite having a larger semimajor axis, a=43.6 AU,
than Pluto, a=39.8 AU.
Another intriguing spectroscopic result comes from
Javier Licandro’s observations of 136472 (2005 FY 9 ). He
finds that CH 4 -ice bands in the spectra of 136472 (2005
FY 9 ) are much deeper than the CH 4 -ice bands in the spectra