Halfway Around the World for 5 Minutes of data

Halfway Around the World for 5 Minutes of data

Learning about the atmosphere of Pluto

Jeff RegesterGreensboro Day School

Outline

• History of Pluto and Outer Solar System science

• Occultations• New Horizons

Pluto’s Discovery

Discovered by accident, on purposeby 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

Occultationan eclipse of a star

1992 Discovery of KBOs

Jewitt & Luu1992 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

Keck

HST

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 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 Bendingangle=>

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 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; < ~627 nm)

Observations - Mt. John(Red channel ; > ~627 nm)

Mt. Canopus

Observations - Portable Telescope (Tasmania)

New Horizons on its way

July 13th, 2015

Questions?