PHYSIQUE DE L'ATMOSPHÈRE DE PLUTON ET TAILLE DE CHARON DÉDUITES D'OCCULTATIONS STELLAIRES 2002-2006 Bruno Sicardy Obs. Paris - LESIA and occcultation Team Thomas Widemann François Colas Atelier 3ème zone, Nantes 11-12 janvier 2007

probed by occultations Pluto and Charon probed by occultations  special moment: equinox in 1988, perihelium in 1989 (period 248 years)  effects on N2 pressure-equilibirum atmosphere?  Charon's size? ( density ?)  Charon's surface gravity ~ 1/2 Pluto's gravity  possibility of atmosphere?

complex interplay of large distance variations & drastic seasonal effects C.J Hansen & D.A. Paige Icarus, 120, 247-265 (1996)

2001 2011 2020 Pluto motion in the sky

Pluton 20 juil. 2002

P131.1 August 21, 2002

temperature contrast: Sicardy et al. Nature, 10 July 2003 spikes: scintillation in Pluto’s atmosphere warmer near pole temperature contrast: cooler near equator

Sicardy et al. Nature, July 2003 Imm. Eme. 

Sicardy et al. « Large changes in Pluto’s atmosphere as revealed by recent stellar occultations » Nature, 10 July 2003

2006 ? 2002 pressure doubled! 1988

rP 1988 B'P 2002 2006 rN Time

10 bar 1 bar 0.1 bar 1900 2000 2100 C.J Hansen & D.A. Paige Icarus, 120, 247-265 (1996)  10 bar  1 bar 0.1 bar 1900 2000 2100

Pluto in 1988

Pluto in 2002

measuring Charon

0.89" 2UCAC 26257135 (D. Herald, Aug. 2004)

VLT/NACO K band, Charon occultation 11 July 2005 Pluto 1" star + Charon

R= 603.61.4 km Sicardy et al., Nature 439, 52, 2006 « Charon’s size and an upper limit on its atmosphere from a stellar occultation »

100 K - CH4 56 K - N2 56 K

Atmosphere: limit is model dependent, e.g. Some conclusions: Atmosphere: limit is model dependent, e.g. CH4 with inversion layer: psurf < 15 nbar …or… N2 isothermal 56 K: psurf < 110 nbar etc… Charon’s size: RC = 603.6  1.4 km Charon’s density: C = 1.65  0.06 g cm-3 (taken from Buie et al. AJ. 132, 290, 2006, NB. P = 2.03  0.06 g cm-3 for Pluto) Possibility to retrieve Pluto’s radius with accurate Charon’s accurate size --> refine atmospheric model cf. The Astronomical Journal, 132:290 -298, 2006 July ORBITS AND PHOTOMETRY OF PLUTOﾕS SATELLITES: CHARON, S/2005 P1, AND S/2005 P2 M. W. Buie, W.M. Grundy, E. F. Young, L. A. Young, A. Stern Barre d'erreur plus grande que ce que je trouve?

recent & future stuff…

12 June 2006 Pluto occultation

1988 2002

12 June 2006, Australia Stockport Blue Mountains Hobart

Stockport 50 cm 20 cm Blue Mountains 40 cm Hobart Time (sec UT)

99.7% c.l. 2 68.3% c.l. pressure expansion factor since 2002

1988 2002

2006

10 5 2 1 pressure @ 1215 km (bar) time (year) Hansen & Paige, Icarus 120, 247 (1996) 10 1 5 2 New Horizon 2006 2002 1988 time (year)

2007: four Pluto & co events?

Nix, 22 mars 2007

Hydra 2.1"

Pluto **et** Hydra 12 mai 2007 Paranal & La Silla Pluton 14 juin 2007 Paranal, La Silla & SOAR

en cours: prédictions d'occultations par de gros TNO Eris, 2005 FY9, 2003 EL6, Sedna, Orcus, Quaoar, Varuna, … (voir présentation T. Widemann)

… merci Paranal Jul 2005

a tenuous atmosphere: Pluto