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  M Pluto = M Mercury /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  M Eris = 1.27 M Pluto 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) shape 2 , (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects 3 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 trans Neptunian objects.

Occultation Overview Temperature Pressure => Extinction Refractivity => Bending angle => Flux Position in shadow

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 N 2 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 13 th , 2015

Questions?