Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.stsci.edu/~mutchler/talks/Pluto_AAS.pdf Äàòà èçìåíåíèÿ: Mon Jan 23 19:54:38 2006 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 12:05:15 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: star trail

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

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?

American Astronomical Society Science Writers Seminar
9 January 2006

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

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

Advanced Camera for Surveys (ACS)

The discovery of Pluto in 1930, and confirmation

The discovery of Pluto's moon Charon in 1978

Clyde Tombaugh

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

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Everything we know about Pluto
· 1930 Pluto discovered
· · · · 1955 1965 1973 1976 ; eccentric orbit * rotation period 6.4 days stable 3:2 resonant orbit with Neptune obliquity > 90 deg * methane ice on surface; size constrained

1 Pluto has not given up it's secrets very easily over the first 75 years...

Discovery of the Kuiper Belt in 1992

· 1978 Charon discovered; "binary planet" * · 1980 Occultation reveals Charon radius to be 600 km · 1985 Pluto-Charon mutual events begin

Everything we know about Pluto ...and has seemed like the "oddball".
· · · · · 1986 1987 1988 1989 1992

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Pluto & Charon radii, albedos, colors Pluto density is 2 g/cm3 Pluto orbit chaotic; atmosphere, polar caps Pluto & Triton similar, structure in atmosphere Nitrogen and CO ice, density disparity

· 1992 Discovery of the Kuiper Belt
· 2001 Binary Kuiper Belt objects (KBOs)

· 2005 Two more moons discovered!

Discovery of two new moons of Pluto

Early Hubble observations of Pluto and Charon

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 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 · Hal's request, June 13...

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

15 May 2005, frame 1

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

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

15 May 2005, frame 2

15 May 2005, frame 3

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

Looking for real objects among all the artifacts...

15 May 2005, frame 4

15 May 2005, sum 4 frames

Looking for real objects among all the artifacts...

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

15 May 2005, median 4 frames

18 May 2005, frame 1

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

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

18 May 2005, frame 2

18 May 2005, frame 3

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

18 May 2005, frame 4

18 May 2005, sum 4 frames

"Clean" image

"Clean" image

18 May 2005, median 4 frames

15 May 2005, median 4 frames

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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

Initial thoughts
· Too easy ?!? · Well-designed program: long exposure times (but not too long), two epochs...even gap 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 much farther out, but they don't violate dynamical constraints (Stern, 1994)

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!

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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)

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?

The "quadruple planet" Pluto
Visual magnitude Pluto 14.2 Diameter Orbital radius * (barycentric) Orbital period * 6.387 days

2328 km +/- 42 km 1208 km +/- 4 km 61-167 km

Charon

16.2

6.387 days

S/2005 P 1

22.93 +/- 0.12 23.38 +/- 0.17

64,700 km 38.2 days (3.7x Charon) (~6x Charon) 49,400 km 25.5 days (2.8x Charon) (~4x Charon)

S/2005 P 2

46-137 km

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

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

What does a "quadruple planet" look like?

P1 P2
2300 km 1200 km ~100 km

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Announcement and publications "Xena & Gabrielle"

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:

The 10th planet?

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

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"

Xena

Pluto

Moon

Earth

Kuiper Belt
2016-2020

Pluto
July 2015

Jupiter
March 2007

Launch
Jan 2006

New Horizons mission

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

http://pluto.jhuapl.edu

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

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

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00 00

Launch currently set for:

January 17, 2006 1:24 PM EST

Questions?

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

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