The discovery of two new satellites of Pluto

Max Mutchler Space Telescope Science Institute Open Night 3 January 2006

Andy Lubenow 1956 - 2005

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)

1 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?

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

Percival Lowell Vesto Slipher Clyde Tombaugh

The discovery of Pluto in 1930, and confirmation

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

• 1950 Kuiper & Humason, 1950 (didn’t find Charon) • 1978 Christy & Harrington (serendipitous discovery of Charon; above) • 1991 Stern 1991: found nothing beyond 6 arcsec • 2005 Gladman & ??? paper that seemed to doom Weaver

The slowly emerging picture of Pluto

3 Charon 1200 km

Earth Pluto Moon 12,800 km 2300 km 3000 km

4 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 Neptune given up it’s secrets • 1973 obliquity > 90 deg * • 1976 methane ice on surface; size constrained very easily over • 1978 Charon discovered; “binary planet” * the first 75 years… • 1980 Occultation 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; 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.

5 Early Hubble observations 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…

6 Hubble Servicing Mission 3B

Advanced Camera for Surveys

Calibrating and drizzling ACS images

The Whirlpool Galaxy M51

7 15 May 2005, frame 1

15 May 2005, frame 2

15 May 2005, frame 3

8 15 May 2005, frame 4

15 May 2005, sum 4 frames

15 May 2005, median 4 frames

9 18 May 2005, frame 1

18 May 2005, frame 2

18 May 2005, frame 3

10 18 May 2005, frame 4

18 May 2005, sum 4 frames

18 May 2005, median 4 frames

11 15 May 2005, median 4 frames

Finding needles in the haystack…

15 and 18 May 2005, sum 8 frames

P1

Charon

P2

15 and 18 May 2005, median 8 frames

12 Initial thoughts

• Too easy?!? Well designed program • Two of them?!? • Surpised they are so close in to Pluto • Surpised there were two – one would have been amazing…what does 2 tell us.

Confirmation

• Independent discovery in Aug 2005 by Andrew Steffl (SwRI in Boulder, Colorado) • Checklist of alternate explanations (proceed with extreme paranoia): detector artifacts (show)? Plutinos? KBO? Neptune Trojans? • Search other existing data: Hubble, Subaru • Our own ground-based attempts to image the new moons: Keck, VLT, Gemini (bad timing) • Hubble followup in Feb 2006 (2 gyros!) • Confident enough to announce on 31 Oct 2005

13 Attempts to image the new satellites with ground-based observatories

Gemini (Hawaii) Very Large Telescope (Chile)

The “checklist” of possible explanations • Artifacts from the detector or optics: hot pixels, ghosts, scattered light (show some; Hartig)? • Background binary KBOs? Binary KBO? • Plutinos or Neptune Trojans? • Expecting moons much farther out; hiding in plain view, front and center; MT pipeline! • Predicted small chance of one KBO in entire WFC field; odds of two vanishingly small • New moons of Pluto!

Preliminary assumptions and implications • Orbits are co-planar with Charon, and nearly circular • Probably formed primordially with Charon (collision), not later (captured) • Possible dust arcs • No other moons of similar magnitude (unless artifacts hid them in June)

14 Pre-discovery observations in 2002

• Hubble program 9391 by Buie & Young • ACS / HRC with blue and visual filters • 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?

The “quadruple planet” Pluto

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 +/- 4 km

S/2005 P 1 22.93 61-167 km 64,700 km 38.2 days +/- 0.12 (99 mi) (3.7x Charon) (~6x Charon)

S/2005 P 2 23.38 46-137 km 49,400 km 25.5 days +/- 0.17 (99 mi) (2.8x Charon) (~4x Charon)

* These numbers assume co-planar and circular orbits for P1 and P2

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

P1

P2

2300 km 1200 km ~100 km

15 What does a “quadruple planet”look like?

Announcement on October 31 2005

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)

“Xena & Gabrielle”

The 10th planet?

16 Xena

Pluto Moon Earth

Should we call Pluto a planet?

• I’m neutral. But some things to consider… • Is Pluto just the first Kuiper Belt “ice dwarf” discovered? • Ceres was called a planet for ~50 years, then “demoted” to asteroid (a precedent) • Is larger Xena the 10th planet? Smaller Sedna, Quaoar? • Will we have only 8 planets, or hundreds of them? • Is this a problem, is it progress…a healthy “controversy”? • The IAU is working on it

17 The next great Voyagers Voyage of Discovery… Launched in 1977

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

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

Good luck New Horizons!

Hal Weaver

Johns Hopkins University Applied Physics Lab and New Horizons Project Scientist

Pluto: A Little Background

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

Until the 1990s, Pluto seemed to be a misfit

18 An Historic Journey

The Initial Reconnaissance of The Solar System’s “Third Zone” KBOs Pluto-Charon Jupiter System 2016-2020 July 2015 March 2007

Launch Jan 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 Hubble Images of Pluto Are Still Crude

19 Pluto Continues to Surprise Us Two New Moons Discovered

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

A Reconnaissance Expedition To the Kuiper Belt & Pluto-Charon

New Horizons Launch Vehicle

Centaur Forward 5-meter Short Payload Load Reactor Fairing (68 ft) Payload Centaur Interstage Adapter (PLA) Adapter (12.5 ft Dia) 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

20 New Horizons to the Pad

New Horizons Launch Site

New Horizons Science Team

21 Baseline Mission Design

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

Two Hour Daily Launch Window

Launch Window Opens Launch Time (EST) 17:30 16:30 15:30 14:30 13:30 12:30 11:30 10:30 2/2/06 2/4/06 2/6/06 2/8/06 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

Launch Date

Pluto-Charon Encounter

Pluto-Charon Encounter Geometry – Arrival July 14, 2015

Charon-Earth Occultation Pluto-Earth Occultation 14:17:50 12:49:50

Charon 13:40

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

Pluto-Sun Occultation 11:40 12:49:00 Charon C/A • 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 • Position and lighting at Pluto C/A 11:59:00 • Distance relative to body center 11,095 km 13.77 km/s

22 Encounter Highlights ¾ Over six months of encounter science at Pluto ¾ Exceed Hubble resolution for almost 3 months ¾ Map entire sunlit areas of Pluto and Charon ¾ Make global composition maps of Pluto and Charon ¾ Map Pluto and Charon surface temperatures 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

New Horizons “Firsts”

¾ First mission to Pluto. ¾ First since launch Voyager in 1977 to an unexplored planet. ¾ First mission to explore a double planet. ¾ First mission to explore an ice dwarf. ¾ First mission to study Kuiper Belt Objects. ¾ Fastest space mission ever launched. ¾ First PI-led outer planets mission. ¾ First planetary mission to carry a student built instrument. ¾ First outer planets mission led by APL and SwRI.

NH Science Payload

23 Unexplored Territory

1990 USA Stamp

Someday, Hopefully

BACKUP SLIDES

24 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 atmosphere of Pluto 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 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: 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

Why Go to Pluto Now?

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. ¾ Atmospheric collapse probability increases with time. ¾ Pluto’s approaching winter solstice nightfall costs ~200,000 km2/yr

http://pluto.jhuapl.edu

13 17 00 00

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

25 Questions?

… AND TWO LITTLE MOONS ! More information: http://www.boulder.swri.edu/plutonews http://pluto.jhuapl.edu

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