Is Pluto a Planet? Dr John K. Davies UK Astronomy Technology Centre, Royal Observatory, Edinburgh, Scotland

Executive Summary

The classical solar system

Planet Uranus imaged from Voyager 2.

Planet Neptune from Voyager 2.

Percival Lowell

Lowell’s Tomb, shaped like Planet Saturn

Clyde Tombaugh and the Pluto Telescope.

Discovery of Pluto, 1930

Orbits of Pluto and Neptune.

Nucleus of Halley’s Comet

Pluto is Shrinking

Pluto is covered with ice.

Pluto and Charon (Gemini Observatory)

Pluto should have vanished by now !

Mercury and Venus: Planets without Moons

243 Ida and Dactyl Ida: Size about 56 km long. Dactyl: Size about 1.5 km.

45 Eugenia and its moon. Eugenia size ~215km Satellite size ~13 km Period ~4.7 days

Pluto has an atmosphere

New Horizons Mission-Pluto Flyby, July 2015.

Comet Hale-Bopp

Comet Orbits Long Period Comet, like Hale-Bopp Short Period Comet. Interstellar comet (never seen)

Gerard Kuiper

Kenneth Edgeworth

Jane Luu and Dave Jewitt

University of Hawaii 2.2m Telescope

Discovery of 1992 QB 1

The Classical Kuiper Belt

The Plutinos

1998 WW31 a Kuiper Belt Object with a satellite

Orbital Elements and Stable Regions

Some of the the largest known Kuiper Belt Objects Late 2000 Varuna Discovered

November 2003 Sedna Announced

Sedna: EKO or Oort Cloud Object?

Sedna. Planet10?

The Discoveries Continue June Quaour discovered. Late Orcus (2004 DW 4 ) announced July Ortiz et al announce ‘discovery’ of 2003 EL 61 July Brown et al announce, via press release, existence of 2003 UB 313 amidst allegations of ‘hacking’ by Ortiz et al

2003 EL 61 Irregular, rocky object with a glazing of ice. Rotates every 4 hours. Has two satellites.

2003 UB 313 aka ‘Xena’

2003 UB 313 aka Xena

2003 UB 313 aka ‘Xena’

What makes a planet? It goes around a star.

Io and the Moon are not planets because they don’t go around a star.

What makes a planet? It goes around a star. It does not generate heat internally.

Jupiter is a planet. since it is not heated by nuclear reactions.

What makes a planet? It goes around a star. It does not make heat by nuclear reactions. It is spherical.

So MOST asteroids are not planets since they have not collapsed to spherical shapes.

What makes a planet? It goes around a star. It does not make heat by nuclear reactions It is (more-or-less) spherical. It is bigger than 1000km in diameter

IAU Committees : First attempts at planet definition split community almost equally so new panel formed. 2006: Committee Meets in Paris to draft proposal for Prague IAU meeting in August

Sunday 13th: Draft IAU resolution sent to press. Allows 12 planets and potential for many more.

3 New Planets

Lots of Potential New Planets

Thursday 17th: Draft proposal slammed by Div III dynamicists

Tuesday 22 nd lunchtime: Further Modified Draft Presented

New proposal slammed even harder!

Tuesday 22 nd 1800hr: Further modifications seem to be getting closer to consensus

Wednesday 23 rd More modifications and coffee break debates over whether a dwarf-planet is the same thing as a “dwarf planet”.

Wednesday 23 rd More modifications and coffee break debates over whether a dwarf-planet is the same thing as a “dwarf planet”. and…. If a dwarf planet is a kind of planet or a whole different thing.

Thursday 24 th : The final Countdown 5A. A Planet is round, goes around the Sun and dominates its local space. A dwarf planet is round, goes around the Sun, has not cleared its local space and is not a satellite. Everything else is a small solar- system body 5B Change Planet to Classical Planet

Thursday 24th: The final Countdown 6A Pluto is a dwarf planet by the above definition and is recognised as the prototype of a new class of trans-Neptunian Objects. 6B This class of dwarf planets will be called Plutonids

Thursday 24th: History is Made 5A. A Planet is round, goes around the Sun and dominates its local space.

Thursday 24th: History is Made 5A. A Planet is round, goes around the Sun and dominates its local space. 5B Change Planet to Classical Planet

Thursday 24th: History is Made 5A. A Planet is round, goes around the Sun and dominates its local space. 5B Change Planet to Classical Planet 6A Pluto is a “dwarf planet” and the prototype of a new class of TNO’s

Thursday 24th: History is Made 5A. A Planet is round, goes around the Sun and dominates its local space. 5B Change Planet to Classical Planet 6A Pluto is a “dwarf planet” and the prototype of a new class of TNO’s 6B This class of dwarf planets will be called Plutonoids

Mike Brown’s Reaction

Some Other Astronomer Reactions

The People’s Reaction

The Astrologer Reaction. “Scorpio’s can be extremely explosive, and very direct, and this may be the trigger that makes them explode” Milton Black, Australian Astrologer “This is a moment I’ve been waiting for, people are finally talking about Charon” Eric Francis, Minor Planet Astrologer

Pluto is a small icy dwarf planet Like Neptune’s moon Triton

..and a member of the Kuiper Belt Pluto

Is Pluto a Planet? What do you think?

Clap for Yes, Pluto is a Planet Cheer for No, Pluto is NOT a planet Yes No

ATC Clapometer Clap Cheer Standby Mode: Quiet Please

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Clap for Yes, Pluto is a Planet Cheer for No, Pluto is NOT a planet Yes No

Clap for Yes, Pluto is a Planet Cheer for No, Pluto is NOT a planet Yes No

Clap for Yes, Pluto is a Planet Cheer for No, Pluto is NOT a planet Yes No

Clap for Yes, Pluto is a Planet Cheer for No, Pluto is NOT a planet Yes No

Clap for Yes, Pluto is a Planet Cheer for No, Pluto is NOT a planet Yes No

Clap for Yes, Pluto is a Planet Cheer for No, Pluto is NOT a planet Yes No

Thanks very much!

Bye for now, Drive safely.

Is Pluto a Planet? Presented by: John Davies and Suzie Ramsay Howat. Written by: John Davies Thanks to: Jason Cowan, Chad Trujillo, Lowell Observatory archives, NASA, Yerkes Observatory, Dave Jewitt, Jane Luu, Martin Duncan and John Spencer

For more information. Published by CUP, get it from Amazon.

Mutual Eclipses of Pluto and Charon

Comet Ring as predicted by Fred Whipple in 1964, virtually what we today call the Kuiper Belt

But 4 of these are no longer in lists of planets published today Ceres Vesta Pallas Juno Sun Venus Earth Mars According to ‘First Steps to Astronomy and Geography’, Hatchard & Son, London, 1828 there are 11 planets. Mercury, Venus, Earth, Mars, Vesta, Juno, Ceres, Pallas, Jupiter, Saturn and Herschel (Uranus)

Tradition in Astronomy Constellations Lunar Sea!