Waves in Pluto's Upper Atmosphere

Abstract

Observations of the 2007 March 18 occultation of the star P445.3 (2UCAC 25823784; R = 15.3) by Pluto were obtained at high time resolution at five sites across the western United States and reduced to produce light curves for each station using standard aperture photometry. Global models of Pluto's upper atmosphere are fitted simultaneously to all resulting light curves. The results of these model fits indicate that the structure of Pluto's upper atmosphere is essentially unchanged since the previous occultation observed in 2006, leading to a well-constrained measurement of the atmospheric half-light radius at 1291 ± 5 km. These results also confirm that the significant increase in atmospheric pressure detected between 1988 and 2002 has ceased. Inversion of the Multiple Mirror Telescope Observatory light curves with unprecedented signal-to-noise ratios reveals significant oscillations in the number density, pressure, and temperature profiles of Pluto's atmosphere. Detailed analysis of this highest resolution light curve indicates that these variations in Pluto's upper atmospheric structure exhibit a previously unseen oscillatory structure with strong correlations of features among locations separated by almost 1200 km in Pluto's atmosphere. Thus, we conclude that these variations are caused by some form of large-scale atmospheric waves. Interpreting these oscillations as Rossby (planetary) waves allows us to establish an upper limit of less than 3 m s −1 for horizontal wind speeds in the sampled region (radius 1340-1460 km) of Pluto's upper atmosphere.

Precise predictions of stellar occultations by Pluto, Charon, Nix, and Hydra for 2008–2015

“…Indeed, about 10 km below 1215 km, there is a remarkable thermal inversion, which is probably caused by methane heating (see Yelle & Lunine 1989;Lellouch et al 2009, for details). An additional interesting feature in Pluto's atmosphere are gravity and/or Rossby waves detected via stellar occultation (Hubbard et al 2009;Person et al 2008;McCarthy et al 2008).…”

Constraints on Charon's Orbital Elements From the Double Stellar Occultation of 2008 June 22

“…It corresponds to the distance of the observer to the shadow center where the stellar flux reaches the half of its unocculted value. Current published values for r 1/2 are r 1/2 = 1213 ± 6 km for the 2002 August 21 occultation (Elliot et al 2003), r 1/2 = 1208 ± 4 km, and r 1/2 = 1216 ± 8.6 km for the 2006 June 12 occultation (see Elliot et al 2007 andYoung et al 2008, respectively) and r 1/2 = 1207 ± 4 km for the 2007 March 18 event (Person et al 2008). …”

“…Those ellipticities have not been confirmed so far. Actually, another Pluto occultation observed in 2007 indicates, according to Person et al (2008), that horizontal wind speed at typical radii of 1400 km should be less than 3 m s −1 . This is clearly too small for supporting ellipticities as high as 6.6% or 9.1% through centrifugal acceleration of a zonal wind regime.…”

Recent Stellar Occultation Observations Using High-Speed, Portable Camera Systems

“…The viewing geometry of this event, coupled with the slow velocity of P445.3, allowed for an unprecedented probe of Pluto's upper atmosphere. Exceptional-quality data were obtained at MMTO (SNR=336 over one pressure scale height), revealing large-scale, coherent wave structures in Pluto's atmosphere [6,8,10,11]. At the time of writing, these results are not yet in press and we are exploring the relationship between the observed light curve structures and Pluto's atmospheric dynamics.…”