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. Final Resolution for GA-XXVI: Definition of a Planet 24 August

Ceres Asteroid Belt Kuiper Belt Discovered Discovered in 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

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

Wide Field Camera 3 (WFC3): installed

Hubble Servicing Mission 4 11 May

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 calibratedcombined 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

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

Hubble images reveal two new moons of Pluto Pluto on 15 Feb

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 Nix and Hydra discovery observations 24

Hydra Nix Nix and Hydra discovery observations 25 Pluto on 15 May 2005

Hydra Nix Nix and Hydra discovery observations 26 Pluto on 18 May 2005

Hydra Charon Nix Pluto on 15 and 18 May 2005 Nix and Hydra discovery observations 27

Nix and Hydra pre-discovery observations in 2002… …it’s much easier to find them once you know exactly where to look 28

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, (23 February 2006) Pluto's first known satellite, Charon, was discovered 1 in 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 satellites 6. 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). 29

Hubble images reveal two more moons of Pluto 30

4 Pluto moons discovered by Hubble since

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, 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 Numerous pre-discovery detections have now been identified in the Hubble archive, spanning 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 = ± 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

Big collisions in the early Solar System: Earth-Moon formation Pluto and moons 33 ©Don Davis

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. 37