Download Overview Presentation on Pluto and Occultations

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?