The discovery of two new satellites of Pluto

transcript

Max MutchlerSpace Telescope Science Institute

FIT visit18 January 2006

T-minus 4 hours and counting…

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?

Advanced Camera Advanced Camera for Surveys (ACS)for Surveys (ACS)

Hubble Servicing Mission 3B in March 2002: ACS installedHubble Servicing Mission 3B in March 2002: ACS installed

Calibrating, pointing, and drizzling

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)

The discovery of Pluto in 1930, and confirmation

ClydeTombaugh

The discovery of Pluto’s moon Charon in 1978

James Christy & Robert Harrington

U.S. Naval ObservatoryWashington, D.C.

Discovery of the Kuiper Belt in 1992

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

• Discovery on June 15: try it yourself…

15 May 2005, frame 1

Notice the star trails, cosmic rays, chip gap…

Dithering across the chip gap now…see anything?

15 May 2005, sum 4 frames

Looking for real objects among all the artifacts…

15 May 2005, median 4 frames

Looking for real objects among all the artifacts…

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

Dither across the gap…where are the moons?

“Clean” image

15 and 18 May 2005, median 8 frames

S/2005 P 1

Charon

S/2005 P 2

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

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 assumptionsand 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)

~100 km~100 km

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

2300 km 1200 km2300 km 1200 km

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

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

Animation produced with Celestia

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

The 10th planet?

“Xena & Gabrielle”

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”

PlutoJuly 2015Kuiper Belt

2016-2020

JupiterMarch 2007 Launch

Jan 2006

New Horizons mission

• 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

Charon

0.24°

SunEarth

Pluto-Charon Encounter GeometryArrival 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

Launch currently set for:

January 18, 20061:16 PM EST

8 23 00 00

http://pluto.jhuapl.edu

Questions?

… AND TWO LITTLE MOONS !

http://www.boulder.swri.edu/plutonews http://pluto.jhuapl.eduhttp://hubblesite .org

The discovery of two new satellites of Pluto

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