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The discovery of two new satellites of Pluto

Max MutchlerSpace Telescope Science Institute

Open Night3 January 2006

Andy Andy LubenowLubenow1956 1956 -- 20052005

Hubble Pluto Satellite Search Team reporting the discovery to the New Horizons Science Team

on November 2, 2005 at the Kennedy Space Center

Left to Right: Hal Weaver (JHU/APL), Andrew Steffl (SwRI), S. Alan Stern (SwRI),Leslie Young (SwRI), John Spencer (SwRI), Marc Buie (Lowell Observatory), Bill Merline (SwRI), Max Mutchler (STScI), and…Eliot Young (SwRI)

Overview

• Discovery of Pluto, Charon, and the Kuiper Belt• 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• New Horizons mission update by Hal Weaver• Questions?

Percival Lowell Vesto Slipher Clyde Tombaugh

The search for “Planet X”Lowell Observatory, Flagstaff, Arizona

The discovery of Pluto in 1930, and confirmation

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The discovery of Pluto’s moon Charon in 1978James 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

Earth Pluto Moon12,800 km 2300 km 3000 km

Charon1200 km

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Pluto has not given up it’s secrets very easily over the first 75 years…

Everything we know about Pluto 1

Everything we know about Pluto 2

• 1930 Pluto discovered; eccentric orbit *• 1955 rotation period 6.4 days• 1965 stable 3:2 resonant orbit with Neptune• 1973 obliquity > 90 deg *• 1976 methane ice on surface; size constrained• 1978 Charon discovered; “binary planet” *• 1980 Occultation reveals Charon radius to be 600 km• 1985 Pluto-Charon mutual events begin

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

Early Hubbleobservations of Pluto and Charon

Discovery of two new moons of Pluto

Press release image for new moons: the discovery was surprisingly easy for Hubble with ACS… but not quite as easy as it looks here.

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 15 and May 18, 2005, using only 2 orbits

• Hal’s request, June 13…

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Advanced Camera for SurveysAdvanced Camera for Surveys

Hubble Servicing Mission 3B

Calibrating and drizzling ACS images

The Whirlpool Galaxy M51

15 May 2005, frame 1

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

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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

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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…

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

S/2005 P 1

Charon

S/2005 P 2

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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• 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, Gemini (difficult until spring 2006)• Checklist of alternate explanations: rule them out?• Confident enough to announce on 31 October 2005

The “checklist” of possible explanations

• Artifacts from the detector or optics: hot pixels, optical ghosts, scattered light, etc

• Real foreground/background objects: asteroids? binary KBO? Plutinos?

• New moons of Pluto!

Preliminary assumptionsand conclusions

• Orbits are co-planar with Charon, nearly circular, possibly in stable resonances with each other

• Probably formed primordially with Charon(collision), not later (captured)

• No other moons of similar magnitude (unless artifacts hid them in June; we’d find them in Feb 2006); very compact system

• Pluto first KBO with multiple satellites: implies there are probably many more

Pre-discovery observations in 2002

• Hubble program by Buie & Young

• ACS High Resolution Channel• Primarily designed to map

surface features of Pluto and Charon

• New moons marginally detected

• Further observations will definitively determine orbits, and hopefully confirm these detections: are the satellites where they should be?

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The “quadruple planet” Pluto

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

23.38+/- 0.17

22.93 +/- 0.12

16.2

14.2

Visualmagnitude

25.5 days(~4x Charon)

49,400 km(2.8x Charon)

46-137 kmS/2005 P 2

38.2 days(~6x Charon)

64,700 km(3.7x Charon)

61-167 kmS/2005 P 1

6.387 days1208 km+/- 4 km

Charon

6.387 days2328 km+/- 42 km

Pluto

Orbitalperiod *

Orbital radius *

(barycentric)

Diameter

P1P1

P2P2

~100 km~100 km

Relative sizes of Pluto, Charon, and the two new moons (P1 and P2)

2300 km 1200 km2300 km 1200 km

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

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

Pre-prints available online at:http://http://arxiv.org/archive/arxiv.org/archive/astroastro--phph

The 10th planet?

“Xena & Gabrielle”

Pluto Moon Earth

Xena

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Should we call Pluto a planet?• I’m neutral. But some things to consider…• Is Pluto the first of many Kuiper Belt “ice dwarf”

planets discovered? • Is larger Xena the 10th planet? • Are slightly smaller Sedna, Quaoar planets? • Ceres was called a planet for ~50 years, then

“demoted” to asteroid (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”

Launch currently set for: January 17, 2006

2:11 PM EST

13 17 00 00

http://pluto.jhuapl.eduGood 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…

VoyagersLaunched in 1977

Hal Weaver

Johns Hopkins University Applied Physics Lab

andNew Horizons Project Scientist

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

Pluto: A Little Background

Until the 1990s, Pluto seemed to be a misfit

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An Historic Journey

Pluto-CharonJuly 2015

KBOs2016-2020

Jupiter SystemMarch 2007

The Initial Reconnaissance of The Solar SystemThe Initial Reconnaissance of The Solar System’’s s ““Third ZoneThird Zone””

LaunchJan 2006

The Kuiper Belt Was Unknown Before the 1990s

Large KBOs Abound

Icy Dwarf Planets, or Planetary Embryos

Pluto-Charon: What we know

The Best HubbleImages of PlutoAre Still Crude

Pluto Continues to Surprise UsTwo New Moons Discovered

Toward New Horizons

A Reconnaissance Expedition To the Kuiper Belt & Pluto-Charon

The Highest Priority New Frontiers New Start Recommendation of the Planetary Decadal Survey

New Horizons Launch Vehicle

Centaur InterstageAdapter (12.5 ft Dia)

CCB CylindricalInterstage Adapter

RD-180 Engine Common CoreBoosterTM (CCB)

SingleRL10 Engine

CentaurUpperStage

5-meter Short PayloadFairing (68 ft)

Solid RocketBoosters

Aft TransitionSkirt/Heat Shield

5-MeterPayload FairingBoattail

CentaurAft StubAdapter

Centaur ForwardLoad Reactor

PayloadAdapter (PLA)

Centaur ConicalInterstage Adapter

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New Horizons to the Pad New Horizons Launch Site

New Horizons Science TeamPluto arrival year

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Launch date (2006)

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2dLaunch Period: Jan 11 Launch Period: Jan 11 -- Feb 14, 2006 (35 days) Feb 14, 2006 (35 days)

JGA Pluto-direct

Baseline Mission Design

2007 launch : 14 days; All arrivals 2019-2021

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Launch Date

Launch Time (EST)

Launch Window Opens

Two Hour Daily Launch Window

• S/C trajectory time ticks: 10 min• Charon orbit time ticks: 12 hr• Occultation: center time• Position and lighting at Pluto C/A• Distance relative to body center

Pluto

Charon

0.24°

SunEarth

12:40

13:40

11:40

Pluto-Charon Encounter Geometry – Arrival July 14, 2015

Pluto C/A11:59:0011,095 km13.77 km/s

Charon C/A12:12:5226,937 km13.87 km/s

Pluto-Sun Occultation12:49:00

Pluto-Earth Occultation12:49:50

Charon-Sun Occultation14:15:41

Charon-Earth Occultation14:17:50

Pluto-Charon Encounter

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Encounter HighlightsOver six months of encounter science at PlutoExceed Hubble resolution for almost 3 monthsMap entire sunlit areas of Pluto and CharonMake global composition maps of Pluto and CharonMap Pluto and Charon surface temperaturesDirectly measure Pluto’s atmosphere: its escape rate, its pressure and temperature, and its compositionImprove interior structure models and determine if either Pluto or Charon is differentiated

The most exciting discoverieswill likely be the ones we

Don’t anticipate.

New Horizons “Firsts”

First mission to Pluto.First since launch Voyager in 1977 to an unexplored planet.First mission to explore a double planet.First mission to explore an ice dwarf.First mission to study Kuiper Belt Objects.Fastest space mission ever launched.First PI-led outer planets mission.First planetary mission to carry a student built instrument.First outer planets mission led by APL and SwRI.

NH Science Payload Unexplored Territory1990 USA Stamp

Someday, Hopefully NASA-Specified Pluto-Charon Measurement Objectives

Group 1 Objectives: Characterize the global geology and morphology of Pluto and Charon Map surface composition of Pluto and Charon Characterize the neutral atmosphere of Pluto and its escape rate

Group 2 Objectives: 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

hydrocarbons and nitriles 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: Characterize the energetic particle environment of Pluto and Charon Refine bulk parameters (radii, masses, densities) and orbits of Pluto & CharonSearch for magnetic fields of Pluto and Charon Search for additional satellites and rings

Required

Desired

Important

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Why Go to Pluto Now?Mission Trajectory

Time-Criticality Factors:JGA Pluto trajectory is available in 2006 but, after that, not until 2018.Atmospheric collapse probability increases with time.Pluto’s approaching winter solstice nightfall costs ~200,000 km2/yr

JupiterUranus

Saturn

LaunchJanuary 2006

Pluto-Charon EncounterSummer 2015

Neptune

Jupiter Gravity Assist FlybySpring 2007

Questions?

… AND TWO LITTLE MOONS !

More information:http://www.boulder.swri.edu/plutonewshttp://pluto.jhuapl.edu