The discovery of four small moons of Pluto with the Hubble...

Pluto

Charon

(large moon)

Max Mutchler Research & Instrument Scientist

Space Telescope Science Institute

Hubble Science Briefing

6 December 2012

The discovery of four small moons of Pluto

with the Hubble Space Telescope

Credit: NASA, ESA and G. Bacon (STScI)

American Museum

of Natural History

“ Hey Dad, where is Pluto?”

2

The IAU therefore resolves that planets and other bodies in our Solar System, except

satellites, be defined into three distinct categories in the following way:

(1) A “planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for

its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium

(nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

(2) A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient

mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic

equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and

(d) is not a satellite.

(3) All other objects, except satellites, orbiting the Sun shall be referred to collectively as

“Small Solar System Bodies”.

Pluto is a "dwarf planet" by the above definition and is recognized as the prototype of a new

category of trans-Neptunian objects. For now, Charon is considered just to be Pluto’s moon.

The idea that Charon might qualify to be called a dwarf planet on its own, may be considered

later.

http://www.iau2006.org

Final Resolution for GA-XXVI:

Definition of a Planet

24 August 2006

3

Ceres

Asteroid Belt Kuiper Belt Discovered 1801-1851 Discovered in 1992

4 credit: A. Feild (STScI)

“It’s like, since being kicked out

of the planet gang, Pluto

decided to form a rival Solar

System. Good on Pluto, I say.” -- comic Dean Burnett

5 http://www.nytimes.com/2012/07/13/science/space/astronomers-spot-fifth-moon-orbiting-pluto.html

Galileo’s telescopic discovery of Jupiter’s moons

6

Hubble Space Telescope

7

Hubble Servicing Mission 1

December 1993

Wide Field Planetary Camera 2

8

The Advanced Camera for Surveys (ACS)

was installed in 2002…and failed in 2007 9

Wide Field Camera 3 (WFC3): installed 2009

10

Hubble Servicing Mission 4

11 May 2009

11

5 days of

spacewalking

12

Goddard Spaceflight Center…16-hour shift during the ACS repair and first tests!

13

Hubble

image

calibration

and reduction

raw

calibrated combined

corrected

14

Recognizing and characterizing the many instrument artifacts

(and not being fooled by them)

An optical “ghost” (not a moon) in Hubble imaging of

asteroid Lutetia (in support of the Rosetta mission) 15

The discovery of

Pluto in 1930

Clyde

Tombaugh

16

Blink-comparator

that Tombaugh

used to compare

two images,

discovering Pluto

by its motion:

basically the

same method we

still use…

17

Pluto discovery images

18

Pluto discovery images

19

The discovery of Pluto’s

moon Charon in 1978 (which required some imagination)

James Christy &

Robert Harrington

U.S. Naval Observatory

Washington, D.C.

20

Jim Christy

Annette and Patsy Tombaugh

Jim Christy

New Horizons launch

19 January 2006

21

Hubble images reveal

two new moons of Pluto

Pluto on 15 Feb 2006 22

Nix and Hydra discovery observations

• Wide Field covers entire

orbital stability zone, but

all the action is very

close to Pluto

• Pluto and Charon near

chip gap for initial

discovery of Nix and

Hydra: peek-a-boo!

23

Pluto on 15 May 2005


24

Hydra

Nix


25


Hydra

Nix


26


Hydra

Charon

Nix

Pluto on 15 and 18 May 2005


27

Nix and Hydra

pre-discovery

observations in

2002…

…it’s much easier

to find them once

you know exactly

where to look

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Discovery of two new satellites of Pluto

H. A. Weaver, S. A. Stern, M. J. Mutchler, A. J. Steffl, M. W. Buie, W. J. Merline,

J. R. Spencer, E. F. Young and L. A. Young

Nature 439, 943-945 (23 February 2006)

Pluto's first known satellite, Charon, was discovered1 in 1978. It has a diameter

(1,200 km) about half that of Pluto, which makes it larger, relative to its primary, than

any other moon in the Solar System. Previous searches for other satellites around Pluto

have been unsuccessful, but they were not sensitive to objects 150 km in diameter and

there are no fundamental reasons why Pluto should not have more satellites6.

Here we report the discovery of two additional moons around Pluto, provisionally

designated S/2005 P 1 (hereafter P1) and S/2005 P 2 (hereafter P2), which makes

Pluto the first Kuiper belt object known to have multiple satellites. These new satellites

are much smaller than Charon, with estimates of P1's diameter ranging from 60 km to

165 km, depending on the surface reflectivity; P2 is about 20 per cent smaller than P1.

Although definitive orbits cannot be derived, both new satellites appear to be moving in

circular orbits in the same orbital plane as Charon, with orbital periods of 38 days (P1)

and 25 days (P2).

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Hubble images reveal

two more moons of Pluto

30

4 Pluto moons discovered by Hubble since 2005

31

Pluto's P4 and P5: Latest Results for Pluto's Tiniest Moons

Showalter, Mark R.; Weaver, H. A.; Stern, A.; Steffl, A. J.; Hamilton, D. P.;

Buie, M. W.; Merline, W. J.; Young, L. A.; Mutchler, M.; Soummer, R.; Throop, H. B. American Astronomical Society, DPS meeting 44, 304.07

We report on the discovery and subsequent analyses of "P4" and "P5", Pluto's fourth and

fifth known moons (officially designated S/2011 (134340) 1 and S/2012 (134340) 1).

P4 was discovered in Hubble Space Telescope images from June-July 2011. Numerous

pre-discovery detections have now been identified in the Hubble archive, spanning 2005-

2011. These detections provide a long time baseline for determining the body's orbital

elements. Based on a preliminary analysis, P4 has an orbital period P = 32.17 ± 0.01

days, placing it at a semimajor axis a 59,500 km, between the orbits of Nix and Hydra. It

appears to fit the general trend of orbital elements in the Pluto system, with Nix near the

1:4 mean motion resonance with Charon, P4 near the 1:5, and Hydra near the 1:6.

The size of P4 depends on the assumed geometric albedo: diameter = 14 km if its albedo

0.35, comparable to that of Charon, or 40 km if it has a much darker albedo 0.04, which

would be more typical of other Trans-Neptunian Objects.

P5 was discovered in Hubble images from June-July 2012 and is roughly half as bright as

P4. It orbits interior to Nix with P = 20.2 ± 0.1 days or a 42,000 km, raising the possibility

of an association with Charon's 1:3 resonance. This configuration of five moons in co-

planar, near-circular, near-resonant orbits suggests that the bodies formed in place

and/or have undergone significant orbital evolution. We will also report on the search for

faint rings and additional moons. 32

Could there be any hazards for the New Horizons spacecraft

when it flies through the Pluto system on 14 July 2015?

The discovery of additional small moons has raised concerns about the possibility of rings or other

debris structures in the Pluto system that can pose hazards to New Horizons. Even a millimeter-sized

pebble’s impact at New Horizons’ flyby speed – about 14 kilometers per second, or more than 31,300

miles per hour – could seriously damage the spacecraft. Credit: NASA/ESA/A. Feild (STScI)/Sky & Telescope

34

Where is the

New Horizons

spacecraft now?

35 credit: NASA/New Horizons

New

Horizons

Pluto: waiting for its spaceship to come in (July 2015)

Maybe then we’ll be better able to define the word “planet”! 36

credit: JHUAPL/SwRI

Hubble Science Briefing Professional Development Telecon, 12/6/12

Pluto has not easily given up its secrets since being discovered in 1930, and the slow

progress in understanding this small icy world has fueled endless debate over

whether it should be considered a planet. While the presence of moons is not one of

the criteria used to classify whether it is a planet, the discovery of the large moon

Charon in 1978 and four smaller moons discovered by Hubble since 2005 have

helped to further characterize the surprisingly complex Pluto system. The Hubble

observations are also helping the New Horizons mission plan their flyby of Pluto in

July 2015, which will dramatically lift the veil on 85 years of mystery.

Max Mutchler has been working on the Hubble Space Telescope for its entire

mission, now over 22 years. He is a Research and Instrument Scientist at the Space

Telescope Science Institute in Baltimore, Md., and is currently focused on managing a

group of 35 analysts and scientists. Max is an expert on Hubble’s cameras, and is a

member of the Hubble Heritage team, which has produced many of the iconic images

for which Hubble is famous. He also specializes in Hubble observations of Solar

System objects, often in support of planetary missions such as New Horizons (en

route to Pluto) and Dawn (currently exploring the Asteroid Belt). He is a member of

the team that has discovered several new moons of Pluto, including one last July.

Asteroid “6815 Mutchler” was named in honor of Max’s role in these discoveries.

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