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The discovery of two new satellites of Pluto
Max Mutchler Space Telescope Science Institute

T-minus 4 hours and counting...

FIT visit
18 January 2006

Overview
· · · · · · · · · Hubble's Advanced Camera, Discovery Team 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 to Pluto and beyond More information via the web Questions?

Calibrating, pointing, and drizzling Hubble Servicing Mission 3B in March 2002: ACS installed

Advanced Camera for Surveys (ACS)

Hubble Pluto Satellite Search Team
reporting the discovery to the New Horizons Science Team on November 2, 2005 at the Kennedy Space Center

The discovery of Pluto in 1930, and confirmation

Left to Right:

Hal W eaver (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)

Clyde Tombaugh

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Discovery of the Kuiper Belt in 1992
The discovery of Pluto's moon Charon in 1978

James Christy & Robert Harrington U.S. Naval Observatory Washington, D.C.

Discovery of two new moons of Pluto

New satellite discovery observations
· Hubble proposal designed by W eaver, Stern, et al., initially rejected, then accepted when STIS died · Advanced Camera for Surveys (ACS) W ide Field Channel (W FC) 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 · Discovery on June 15: try it yourself...

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

Notice the star trails, cosmic rays, chip gap...

Notice the star trails, cosmic rays, chip gap...

15 May 2005, frame 1

15 May 2005, frame 2

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Dithering across the chip gap now...see anything?

Dithering across the chip gap now...see anything?

15 May 2005, frame 3

15 May 2005, frame 4

Looking for real objects among all the artifacts...

Looking for real objects among all the artifacts...

15 May 2005, sum 4 frames

15 May 2005, median 4 frames

Do it again 3 days later...where are the moons?

Do it again 3 days later...where are the moons?

18 May 2005, frame 1

18 May 2005, frame 2

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Dither across the gap...where are the moons?

Do it again 3 days later...where are the moons?

18 May 2005, frame 3

18 May 2005, frame 4

"Clean" image

"Clean" image

18 May 2005, median 4 frames

15 May 2005, median 4 frames

New moons are roughly 3-4x farther out than Charon, with possible 6:4:1 orbital resonances

S/2005 P 1

Charon

S/2005 P 2

15 and 18 May 2005, median 8 frames

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Initial thoughts
· Why is Pluto suddenly going so easy on us ?!? · Well-designed program: long exposure times (but not too long), two epochs...the gap is OK · Two objects! They somewhat validate each other, and assumptions about their orbits · Surprised they are so close to Pluto and Charon: expecting any moons to be farther out, but they don't violate dynamical constraints (Stern, 1994) · Could they be something other than moons?
· · · ·

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
· · · · · Detector artifacts? Optical "ghosts" or scattered light? Overlapping cosmic rays or star trails? Real, but asteroids? KBO (Plutinos)? New moons of Pluto!

Preliminary assumptions and implications
· Orbits are co-planar with Charon, nearly circular, possibly in stable resonances with each other · No other moons of similar magnitude (unless artifacts hid them); very compact system · Pluto first KBO with multiple satellites: implies there are probably many more · Probably formed primordially with Charon (collision), not later (captured)

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

P1 P2
2300 km 1200 km ~100 km

New moons are roughly 12x smaller than Charon, and 5000x fainter than Charon

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What does a "quadruple planet" look like?
http://www.stsci.edu/~mutchler/pluto_50.html

Announcement and publications

Animation produced with Celestia

W W St St

eaver eaver ern et effl et

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

Pre-prints available online at:

http://arxiv.org/archive/astro-ph

"Xena & Gabrielle"
Xena

The 10th planet?

Pluto

Moon

Earth

Should we call Pluto a planet?
· I'm neutral. But some things to consider... · Is Pluto just 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 re-classified as an 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"

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Kuiper Belt
2016-2020

Pluto
July 2015

Jupiter
March 2007

Launch
Jan 2006

Pluto-Charon Encounter Geometry Arrival July 14, 2015
Charon-Earth Occultation 14:17:50

Pluto-Earth Occultation 12:49:50 Charon

13:40

12:40

Pluto
0.24°

Charon-Sun Occultation 14:15:41 Pluto-Sun Occultation 12:49:00 · · · · · 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

Sun Earth

11:40

Charon C/A 12:12:52 26,937 km 13.87 km/s

New Horizons mission

Pluto C/A 11:59:00 11,095 km 13.77 km/s

http://pluto.jhuapl.edu

Questions?

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Launch currently set for:

... AND TWO LITTLE MOONS ! http://www.boulder.swri.edu/plutonews http://pluto.jhuapl.edu http://hubblesite .org

January 18, 2006 1:16 PM EST

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