Hubble Space Telescopeimaging of Ceres and Vesta

L. McFadden and J.Y. Li (University of Maryland, College Park), J. Parker and E. Young (Southwest Research Institute),

M. Sykes (University of Arizona), P. Thomas (Cornell University), C. Russell and B. Schmidt (University of California, Los Angeles),

M. Mutchler and Z. Levay (Space Telescope Science Institute)Version 22 June 2007

The planet vote of 2006

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”.

http://www.iau2006.org

Final Resolution 5 for GA-XXVI: Definition of a Planet24 August 2006

Historical perspective:how many planets are there?

• Antiquity -- 7 planets; geocentric model (Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn)

• 1550 – 6 planets; heliocentric model (add Earth, remove Moon & Sun)• 1781 – 7 planets (add Uranus) • 1807 – 11 planets (add Ceres, Pallas, Juno, Vesta) • 1845 – 12 planets (add Astraea) • 1846 – 13 planets (add Neptune) • 1851 – 8 planets (exclude objects in Asteroid Belt – any déjà vu?) • 1930 – 9 planets (add Pluto)• 1992 – Discovery of 1992 QB1…the Kuiper Belt! • 2005 – Discovery of Eris (UB313)• 2006 – 8 planets (remove Pluto; don’t add Ceres, Charon, Eris or

other “dwarf planets”)• 2009 – Another vote?

Ceres

Asteroid Belt Kuiper Belt Discovered 1801-1851 Discovered in 1992…or 1930?

Ceres and Pluto: The “ugly duckling”problem of being the first of an entire class

Hubble images of Ceres in January 2004

• Advanced Camera for Surveys (ACS) High Resolution Channel (HRC)

• Filters: F220W, F330W, F555W

• Sub-sampled (dithered) images were drizzled to enhance resolution

• Color composite images: F330W+F555W

• Movies made from lower-resolution images (full phase coverage)

Hubble images of Ceres reveal roundness, surface features, and colors

Three different faces of Ceres

Hubble images of Ceres reveal roundness, surface features, and colors

Three different faces of Ceres

Why does roundness matter ?

Differentiation of the asteroid Ceres as revealed by its shape Thomas, Parker, McFadden, Russell, Stern, Sykes, Young, 2005, Nature Letters, Vol 437

Hubble images of Vesta in May 2007

• Wide Field Planetary Camera 2 (WFPC2); Advanced Camera (ACS) failed in January 2007

• Filters: F439W, F673N, F953N, F1042M• No subsampling dithers: Vesta rotates too fast• Preliminary image deconvolution via Maximum

Entropy Method (MEM); MISTRAL next…• Color composite images: F439W+F673N• Movies and albedo maps

Hubble WFPC2 F439W image of asteroid Vesta in May 2007: raw

Hubble WFPC2 F439W images of asteroid Vesta in May 2007: deconvolved (MEM)

Hubble WFPC2 image of asteroid Vesta: artist’s impression

Hubble WFPC2 F439W images of asteroid Vesta in May 2007: raw

Hubble WFPC2 F439W images of asteroid Vesta in May 2007: deconvolved (MEM)

Hubble WFPC2 F673N images of asteroid Vesta in May 2007: raw

Hubble WFPC2 F673N images of asteroid Vesta in May 2007: deconvolved (MEM)

Hubble WFPC2 F953N images of asteroid Vesta in May 2007: raw

Hubble WFPC2 F953N images of asteroid Vesta in May 2007: deconvolved (MEM)

Hubble WFPC2 F1042M images of asteroid Vesta in May 2007: raw

Hubble WFPC2 F1042M images of asteroid Vesta in May 2007: deconvolved (MEM)

Hubble WFPC2 images of asteroid Vesta in May 2007: color composite

Hubble WFPC2 images of asteroid Vesta in May 2007: color composite movie

http://www.dawn-mission.org

Dawn

Vesta2011

Ceres2015

Launch July 7!