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Halfway Around the World for 5 Minutes of data
Learning about the atmosphere of Pluto
Jeff RegesterGreensboro Day School
In 2004...
A comparison of the size of Sedna, the largest known KBO in 2004, to various planets and moons. (NACO Team, 8.2-meter VLT (Yepun), ESO, apod040827)
2006, The IAU acts• RESOLUTION 5A
The IAU therefore resolves that "planets" and other bodies in our Solar System, except satellites, be defined into three distinct categories in the following way:
(1) A "planet"1 is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
(2) A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape2 , (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.
(3) All other objects3 except satellites orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies".
1 The eight "planets" are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.2 An IAU process will be established to assign borderline objects into either dwarf planet and other categories.3 These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.
goodbye “minor planets”
RESOLUTION 6AThe IAU further resolves:
Pluto is a "dwarf planet" by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.
Occultation Overview
Temperature PressureExtinction
Refractivity Bending
angle=>
Flux Position in shadow
=>=>
Lower Atmosphere Inversion(Ref: Elliot, Person and Qu 2003)
• Small Planet Case• No Ray Crossing• Geometric Optics• Clear Atmosphere
Conclusions from 2006 data• Pluto's bulk atmosphere (geometry):
– 1988 to 2006, pressure has increased by 0.98 ± 0.09 µbar, a factor of 2.17±0.21
– For N2 surface vapor pressure equilibrium, this implies an increase in surface temperature of 1.2-1.7 K.
– Pressures consistant between 2002 and 2006
• Pluto’s upper atmosphere (model fit): – Non-isothermal. dT/dr = -0.127±0.028 K/km– Average (103.9±3.2 K) same as 2002 (104±2 K, isothermal fit),
and 1988 (104.0±7.3 K). – 99.4±3.1 K (ingress, 30.0 S, summer), 105.5±3.5 K (egress, 53.2 N, winter)
despite ~1500 less insolation averaged over the winter latitude, so not tied to insolation (in a straightforward way)
• Pluto’s lower atm, clear assumption (inversion):– As in 1988 & 2002, not isothermal. – Temperature inversion around 1210 - 1220 km.– Ingress & Egress are qualitatively similar, but the density perturbations differ in detail.
• Pluto’s lower atm, haze assumption (inversion, removing haze from model fit)– Top of haze poorly constrained.– Temperature perturbations qualitatively similar to those seen on Earth, Jupiter, Titan