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Home , Atmosphere of Pluto, Clyde Tombaugh, Lowell Observatory, Marc Buie, Moons of Pluto, Percival Lowell

The discovery of two new of

Max Mutchler Space Science Institute Open Night 3 January 2006

Andy Lubenow 1956 - 2005

Hubble Pluto Search Team Overview reporting the discovery to the Science Team on November 2, 2005 at the Kennedy Space Center • Discovery of Pluto, , and the •Early Hubble observations of Pluto • Hubble mission support for New Horizons: discovery of two more Pluto satellites • Confirming and following-up the discovery • Implications, and recent related discoveries

Left to Right: • New Horizons mission update by Hal Weaver Hal Weaver (JHU/APL), Andrew Steffl (SwRI), S. (SwRI), Leslie Young (SwRI), John Spencer (SwRI), ( ), • Questions? Bill Merline (SwRI), Max Mutchler (STScI), and…Eliot Young (SwRI)

The discovery of The search for “ X” Pluto in 1930, , Flagstaff, Arizona and confirmation

Percival Lowell

1 The discovery of Pluto’s Charon in 1978 James Christy and Robert Harrington, U.S. Naval Observatory, Washington, D.C.

• 1950 Kuiper & Humason, didn’t find Charon • 1978 Christy & Harrington, serendipitous discovery of Charon (above) • 1991 Stern: found no more satellites beyond ~100,000 km from Pluto • 2005 Gladman et al. paper -- seemed to doom this Hubble search The slowly emerging picture of Pluto

Charon 1200 km

Earth Pluto Moon 12,800 km 2300 km 3000 km

2 Everything we know about Pluto 1 • 1930 Pluto discovered; eccentric orbit * • 1955 rotation period 6.4 days Pluto has not • 1965 stable 3:2 resonant orbit with given up it’s secrets • 1973 obliquity > 90 deg * • 1976 ice on surface; size constrained very easily over • 1978 Charon discovered; “binary planet” * the first 75 years… • 1980 reveals Charon radius to be 600 km • 1985 Pluto-Charon mutual events begin

Everything we know about Pluto 2 • 1986 Pluto & Charon radii, albedos, colors • 1987 Pluto density is 2 g/cm3 • 1988 Pluto orbit chaotic; , polar caps • 1989 Pluto & similar, structure in atmosphere • 1992 and CO ice, density disparity • 1992 Discovery of the Kuiper Belt • 2001 Binary Kuiper Belt objects (KBOs) • 2005 Two more discovered! P1 and P2.

Early Hubble observations of Pluto and Charon

Discovery of two new New satellite discovery observations

• Hubble proposal designed by Weaver, Stern, et al., initially rejected, then accepted when STIS died • Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) covers entire orbital stability zone • Pluto-Charon near chip gap: peek-a-boo! • 4 long exposures on May Press release image for new moons: the 15 and May 18, 2005, using only 2 orbits discovery was surprisingly easy for Hubble with • Hal’s request, June 13… ACS… but not quite as easy as it looks here.

3 Calibrating and drizzling ACS images

Hubble Servicing Mission 3B

Advanced Camera for Surveys The Whirlpool M51

15 May 2005, frame 1

15 May 2005, frame 2 15 May 2005, frame 3

4 15 May 2005, frame 4 15 May 2005, sum 4 frames

15 May 2005, median 4 frames 18 May 2005, frame 1

18 May 2005, frame 2 18 May 2005, frame 3

5 18 May 2005, frame 4 18 May 2005, sum 4 frames

18 May 2005, median 4 frames 15 May 2005, median 4 frames

Finding needles in the haystack…

S/2005 P 1

Charon

S/2005 P 2

15 and 18 May 2005, sum 8 frames 15 and 18 May 2005, median 8 frames

6 Initial thoughts

• Too easy ?!? Well-designed program • Surprised they are so close to Pluto: expecting moons much farther out • Surprised there were two – one would have been amazing enough, odds small for even one object • Two objects help “confirm” each other, help validate assumptions?

Confirmation and follow-up The “checklist” of possible explanations • Independent discovery in Aug 2005 by Andrew Steffl • Search other existing data: Hubble, Subaru… • Hubble follow-up: impossible until Feb 2006 (2 gyros) • Ground-based attempts to image the new moons in Sep/Oct: Keck, VLT, (difficult until spring 2006) • Artifacts from the detector or optics: hot • Checklist of alternate explanations: rule them out? pixels, optical ghosts, scattered light, etc • Confident enough to announce on 31 October 2005 • Real foreground/background objects: ? binary KBO? ? • New moons of Pluto!

Preliminary assumptions Pre-discovery observations in 2002 and conclusions • Hubble program by Buie & Young • Orbits are co-planar with Charon, nearly circular, • ACS High Resolution Channel possibly in stable resonances with each other • Primarily designed to map • Probably formed primordially with Charon surface features of Pluto and (collision), not later (captured) Charon • New moons marginally • No other moons of similar magnitude (unless detected artifacts hid them in June; we’d find them in Feb • Further observations will 2006); very compact system definitively determine orbits, and hopefully confirm these • Pluto first KBO with multiple satellites: implies detections: are the satellites there are probably many more where they should be?

7 The “quadruple planet” Pluto Relative sizes of Pluto, Charon, and the two new moons (P1 and P2) Visual Diameter Orbital Orbital magnitude radius * period * (barycentric) Pluto 14.2 2328 km 6.387 days +/- 42 km

Charon 16.2 1208 km 6.387 days P1 +/- 4 km P2 S/2005 P 1 22.93 61-167 km 64,700 km 38.2 days P2 +/- 0.12 (3.7x Charon) (~6x Charon) 2300 km 1200 km ~100 km S/2005 P 2 23.38 46-137 km 49,400 km 25.5 days +/- 0.17 (2.8x Charon) (~4x Charon)

New moons are 5000x fainter, 12x smaller, and 3-4x farther out than Charon, with possible 6:4:1 orbital resonances

What does a “quadruple planet” look like? Announcement and publications

Weaver et al, 2005, IAU Circular 8625 Weaver et al., 2006, Nature (accepted) Stern et al., 2006, Nature (accepted) Steffl et al., Astronomical Journal (submitted)

Pre-prints available online at: http://arxiv.org/archive/astro-ph

“Xena & Gabrielle”

Xena

The 10th planet? Pluto Moon

8 Should we call Pluto a planet?

• I’m neutral. But some things to consider… • Is Pluto the first of many Kuiper Belt “ice dwarf” discovered? • Is larger Xena the 10th planet? • Are slightly smaller Sedna, Quaoar planets? • was called a planet for ~50 years, then “demoted” to (a precedent) • Will we have only 8 planets, or hundreds of them? • Is this a problem? Seems like progress to me. • The IAU is working on it…in the meanwhile, it is a harmless and healthy “non-controversy”

Voyagers http://pluto.jhuapl.edu Launched in 1977 Good luck to New Horizons, the next great Voyage of Discovery…

It’s greatest discoveries will surely be the unexpected ones.

It will surely inspire the next generation of math and science students…

13 17 00 00

Launch currently set for: January 17, 2006 2:11 PM EST

Pluto: A Little Background

Distant Pluto was discovered in 1930, by Clyde Tombaugh at Lowell Hal Weaver Observatory, Arizona.

Johns Hopkins University Applied Physics Lab and New Horizons Project Scientist

Until the 1990s, Pluto seemed to be a misfit

9 An Historic Journey Large KBOs Abound

The Initial Reconnaissance of The ’s Icy Dwarf Planets, or Planetary Embryos “Third Zone” KBOs Pluto-Charon System 2016-2020 July 2015 March 2007

Launch Jan 2006

The Kuiper Belt Was Unknown Before the 1990s

Pluto-Charon: What we know Pluto Continues to Surprise Us Two New Moons Discovered

The Best Hubble Images of Pluto Are Still Crude

Toward New Horizons New Horizons Launch Vehicle The Highest Priority New Frontiers New Start Recommendation of the Planetary Decadal Survey Centaur Forward 5-meter Short Payload Load Reactor Fairing (68 ft) Payload Centaur Interstage Adapter (PLA) A Reconnaissance Expedition Adapter (12.5 ft Dia) To the Kuiper Belt & Pluto-Charon Centaur Conical Interstage Adapter CCB Cylindrical Interstage Adapter

Solid Rocket Boosters

Centaur Upper Aft Transition Centaur Single Stage Skirt/Heat Shield Aft Stub RL10 Engine Adapter 5-Meter RD-180 Engine Common Core Payload Fairing BoosterTM (CCB) Boattail

10 New Horizons to the Pad New Horizons Launch Site

Baseline Mission Design

New Horizons Science Team Pluto arrival year 2021 Launch Period: Jan 11 - Feb 14, 2006 (35 days) 2d 2020 4 d 2019 6 d 2018 2d 2017 3 d 2016 18 d 2015 2014 Pluto-direct 2013 JGA 2012 2/1 2/2 2/3 2/4 2/5 2/6 2/7 2/8 2/9 1/11 1/12 1/13 1/14 1/15 1/16 1/17 1/18 1/19 1/20 1/21 1/22 1/23 1/24 1/25 1/26 1/27 1/28 1/29 1/30 1/31 2/10 2/11 2/12 2/13 2/14 Launch date (2006) 2007 launch : 14 days; All arrivals 2019-2021

Pluto-Charon Encounter Two Hour Daily Launch Window Pluto-Charon Encounter Geometry – Arrival July 14, 2015 Launch Window Opens Launch Time (EST) Charon-Earth Occultation Pluto-Earth Occultation 14:17:50 17:30 12:49:50 16:30 Charon 13:40 15:30

14:30 Pluto 12:40 13:30 Earth Charon-Sun Occultation 0.24° 12:30 14:15:41

11:30 Pluto-Sun Occultation 11:40 12:49:00 Charon C/A 10:30 • S/C trajectory time ticks: 10 min 12:12:52 • Charon orbit time ticks: 12 hr 26,937 km • Occultation: center time Pluto C/A 13.87 km/s 2/2/06 2/4/06 2/6/06 2/8/06 • Position and lighting at Pluto C/A 11:59:00 1/11/06 1/13/06 1/15/06 1/17/06 1/19/06 1/21/06 1/23/06 1/25/06 1/27/06 1/29/06 1/31/06 2/10/06 2/12/06 2/14/06 • Distance relative to body center 11,095 km Launch Date 13.77 km/s

11 Encounter Highlights New Horizons “Firsts” ¾ Over six months of encounter science at Pluto ¾ First mission to Pluto. ¾ Exceed Hubble resolution for almost 3 ¾ First since launch Voyager in 1977 to an unexplored planet. months ¾ First mission to explore a . ¾ First mission to explore an ice dwarf. ¾ Map entire sunlit areas of Pluto and Charon ¾ First mission to study Kuiper Belt Objects. ¾ Make global composition maps of Pluto and ¾ Fastest space mission ever launched. Charon ¾ First PI-led outer planets mission. ¾ First planetary mission to carry a student built instrument. ¾ Map Pluto and Charon surface temperatures ¾ First outer planets mission led by APL and SwRI. ¾TheDirectly most exciting measure discoveries Pluto’s atmosphere: its escapewill likely rate, be the its ones pressure we and temperature, and Don’tits composition anticipate. ¾ Improve interior structure models and determine if either Pluto or Charon is differentiated

NH Science Payload Unexplored Territory

1990 USA Stamp

Someday, Hopefully NASA-Specified Pluto-Charon Measurement Objectives

Group 1 Objectives: Required Characterize the global geology and morphology of Pluto and Charon Map surface composition of Pluto and Charon Characterize the neutral and its escape rate Group 2 Objectives: Important Characterize the time variability of Pluto's surface and atmosphere Image Pluto and Charon in stereo Map the terminators of Pluto and Charon with high resolution Map the composition of selected areas of Pluto & Charon at high resolution Characterize Pluto's ionosphere and solar wind interaction Search for neutral species including H, H2, HCN, and CxHy, and other and in Pluto's upper atmosphere Search for an atmosphere around Charon Determine bolometric Bond albedos for Pluto and Charon Map the surface temperatures of Pluto and Charon Group 3 Objectives: Desired Characterize the energetic particle environment of Pluto and Charon Refine bulk parameters (radii, masses, densities) and orbits of Pluto & Charon Search for magnetic fields of Pluto and Charon Search for additional satellites and rings

12 Why Go to Pluto Now? Questions? Mission Trajectory Jupiter Gravity Assist Flyby Pluto-Charon Encounter Spring 2007 Summer 2015

Saturn

Uranus Jupiter

Neptune Launch January 2006

Time-Criticality Factors: ¾ JGA Pluto trajectory is available in 2006 but, after that, not until 2018. … AND TWO LITTLE MOONS ! ¾ Atmospheric collapse probability increases with time. ¾ Pluto’s approaching winter solstice nightfall costs ~200,000 km2/yr More information: http://www.boulder.swri.edu/plutonews http://pluto.jhuapl.edu

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