Gemini Observatory Shows That "10th Planet" Has a Pluto-Like Surface
29 July 2005
Gemini Observatory has obtained a preliminary spectrum of 2003 UB313,
the so-called "10th planet". These observations were obtained on
25, 2005 by Chad Trujillo, a Gemini staff member who is also on the
discovery team for 2003 UB313, the existence of which was formally
announced by the Minor Planet Center in Cambridge, MA on July 29, 2005.
The discovery team (Mike Brown of Caltech, Chad Trujillo of Gemini and
David Rabinowitz of Yale) are still uncertain of the exact size of the
body, but report that it must be Pluto-sized or larger. The body is the
most distant solar system body known to orbit the sun at 97 AU from the
sun, over 3 times farther away than planet Pluto. The "planet" was
originally discovered in late December 2004 with data collected from
Samuel Oschin 1.2 meter telescope at Palomar Mountain, CA.
To better characterize the surface of the object the team obtained
spectra with NIRI (the near-infrared spectrograph) on the much larger 8
meter Gemini North telescope on Mauna Kea, Hawaii. The NIRI spectra
shows strong signatures of methane ice, remarkably similar to the
spectrum of Pluto, which is also dominated by methane ice in
near-infrared observations. Figure 2 shows the spectra of Pluto and
UB313, with arrows marking the "dips" that correspond to methane
features. The same features are readily apparent in both the Pluto and
the 2003 UB313 spectra.
Figure 2: 2003 UB313 spectrum (red, obtained at Gemini Observatory by
Trujillo, Brown and Rabinowitz) and Pluto (black, from Rudy et al.
2003). The "dips" characteristic of methane ice are indicated by red
arrows and are present in both 2003 UB313 and Pluto.
Trujillo states, "We still do not know much about this object, however,
it is clear that it is very similar to Pluto in both size and
composition, at least upon first glance." The presence of methane ice
unusual in that it indicates a primitive surface that has not likely
been heated significantly since the solar system formed 4.5 billion
years ago. "If 2003 UB313 ever got close to the sun, all the methane
would have boiled off immediately," Trujillo continued. "To date, no
has seen methane on any other Kuiper Belt Object, only on Pluto and
Neptune's moon Triton." The distant Kuiper Belt is a collection of
bodies orbiting the sun beyond Neptune, and is likely the parent
population to the comets.
The team have also obtained spectra of the smaller mini-planet 2003
EL61, which was reported on July 28, 2005 by two independent teams: one
from the Sierra Nevada Observatory in Spain and the Brown, Trujillo and
Rabinowitz team. This object is smaller than Pluto, but shows strong
water-ice features, similar to what is seen on the surface of Pluto's
Results will be reported in detail at the 37th annual meeting of the
Division for Planetary Sciences of the American Astronomical Society in
September 2005 at the University of Cambridge, UK.