Transcript Slide 1
Halfway Around the World for 5 Minutes of data Learning about the atmosphere of Pluto Jeff Regester Greensboro Day School Outline • History of Pluto and Outer Solar System science • Occultations • New Horizons Pluto’s Discovery Discovered by accident, on purpose by Clyde Tombaugh, Lowell Observatory, 1930 The Edgeworth-Kuiper Belt Leftovers Moons Charon, discovered in 1978 by Jim Christie, USNO MPluto = MMercury/20 Moons Nix and Hydra, discovered in 2005 by Alan Stern et al, using HST Discovery of Atmosphere, 1988 Occultation an eclipse of a star 1992 Discovery of KBOs Jewitt & Luu 1992 QB1 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) ...and 2005 HST Keck Kepler’s Third Law Dysnomia’s orbit P=16d MEris= 1.27 MPluto Houston, we have a problem! We’ve been here before. 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 6A The IAU further resolves: Pluto is a "dwarf planet" by the above definition and is recognized as the prototype of a new category of transNeptunian objects. Occultation Overview Temperature Flux Bending => => Refractivity => Pressure Position in shadow angle Extinction Chris L. Peterson, Cloudbait Observatory, Colorado Lower Atmosphere Inversion (Ref: Elliot, Person and Qu 2003) • • • • Small Planet Case No Ray Crossing Geometric Optics Clear Atmosphere 12 June 2006 Occultation: Reconstructed Shadow Path Predicting Occultations Ain’t Easy! At the mercy of the clouds. Occultations 12Jun2006 18Mar2007 31Jul2007 Mt. Canopus Obs, Hobart, TAS Luxury! 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 Observations - Mt. John (Blue channel; l < ~627 nm) Observations - Mt. John (Red channel ; l > ~627 nm) Mt. Canopus Observations - Portable Telescope (Tasmania) New Horizons on its way July 13th, 2015 Questions?