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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