[meteorite-list] Observations Show 2005 FY9 Is Very Similar To Pluto

[Ron Baalke]

Isaac Newton Group of Telescopes
Apartado de correos 321
E-38700 Santa Cruz de la Palma
Canary Islands, Spain

Contact:
Javier Méndez, Public Relations Officer
jma @ ing.iac.es

News release date: 13th January, 2006

WHT and TNG Observations Prove that the Large Trans-Neptunian Object 2005 
FY9 is Very Similar to Pluto

Visible and near-infrared spectroscopic observations carried out on August 
1st 2005 by a group leaded by the ING-IAC astronomer Javier Licandro[1] 
using the William Herschel Telescope (WHT) and the Telescopio Nazionale 
Galileo (TNG) at El Roque de Los Muchachos Observatory show that the 
recently discovered trans-neptunian object (TNO) 2005 FY9 is very similar 
to Pluto. Results have been published in the journal Astronomy & 
Astrophysics (Licandro et al., 2006, A&A, 445, 35L).

2005 FY9 is the third brightest known TNO, after 2003 UB313 and Pluto. 
Although discovered early in 2005 by USA astronomers M. Brown and 
co-workers, the discovery wasn't reported until July 29th. The size of 
2005 FY9 is 0.7 times that of Pluto approximately. The semi-major axis of 
its orbit is 46 Astronomical Units (AU, 1 AU=149,597,892 kilometres), the 
perihelion distance is 39 AU and the inclination of the orbit is 29 deg. 
These values are typical of the classical TNO family.

Visible spectroscopy was obtained using the ISIS spectrograph on the WHT, 
and near-infrared spectroscopy was obtained using the NICS spectrograph on 
the TNG. The complete visible and near-infrared spectrum is shown in 
Figure 2 and compared with the spectrum of Pluto and that of pure methane 
ice. Figure 2 clearly shows that the spectra of both TNOs are very 
similar. They are dominated by strong absorption bands produced by methan 
ice. In fact, the absorption bands in the spectrum of 2005 FY9 are deeper 
than in the spectrum of Pluto as a result of the larger abundance of 
methane ice in 2005 FY9. Also the colour of the surface of the TNO is red 
(indicated by the slope of the spectrum), similar to that of Pluto. This 
shows the presence of complex organic compounds in the surface.

The discovery of a Pluto 'twin' in the trans-neptunian belt is relevant as 
Pluto is the only known TNO possessing a small atmosphere. The similar 
size and surface composition of 2005 FY9 are facts that suggest it can 
also have such a tenuous bound atmosphere.

Until now only one known TNO, Pluto, showed the presence of strong methan 
ice absorption bands in the spectrum. However, apart from 2005 FY9, 
recently these bands were also observed in the spectrum of the largest yet 
known TNO, 2003 UB313 (Brown et al., 2005, ApJ, 635, 97). As shown in 
Figure 3, the near infrared spectrum of 2003 UB313 is very similar to that 
of 2005 FY9.

The discovery that 2005 FY9 is very similar to Pluto provides astronomers 
with a new and exciting laboratory for the study of volatile mixing and 
transport, atmospheric freeze-out and escape, ice chemistry, and nitrogen 
phase transitions in Pluto-like objects.

Notes:

[1] The members of the international team led by Javier Licandro (ING-IAC) 
are William Grundy (Lowell Observatory), Ernesto Oliva (FGG-TNG), Marco 
Pedani (FGG-TNG), Noemí Pinilla-Alonso (FGG-TNG) and Gian Paolo Tozzi 
(Osservatorio di Arcetri).

IMAGE CAPTIONS:

[Figure 1:
http://www.ing.iac.es/PR/press/8451.jpg (23KB)]
The size of the largest objects known in the outer Solar System compared 
with the size of the Moon.

[Figure 2:
http://www.ing.iac.es/PR/press/spectrum2005FY9.gif (28KB)]
The spectrum of 2005 FY9 compared with the spectrum of Pluto and that of 
pure methane ice. Notice the strong methan ice absorption bands present in 
the spectrum of both TNOs.

[Figure 3:
http://www.ing.iac.es/PR/press/img19.gif (29KB)]
Near infrared spectrum of 2005 FY9 obtained by Licandro et al. (2006) 
compared with that of TNO 2003 UB313 from Brown et al. (2005). The 
similarity of both spectra shows that the surface composition of both 
objects must be also similar.