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 1905-1973

Kenneth Edgeworth. 1880-1973

Jane Luu and Dave Jewitt

University of Hawaii 2.2m Telescope

Discovery of 1992 QB1

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 2002. Quaour discovered.

• Late 2004. Orcus (2004 DW4) announced• July 2005. Ortiz et al announce ‘discovery’

of 2003 EL61

• July 2005. Brown et al announce, via press release, existence of 2003 UB313 amidst allegations of ‘hacking’ by Ortiz et al

2003 EL61

• Irregular, rocky object with a glazing of ice.

• Rotates every 4 hours.

• Has two satellites.

2003 UB313 aka ‘Xena’

2003 UB313 aka Xena

2003 UB313 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.

• It does not generate heat internally.

Jupiter is a planet.

since it is not heated by nuclear reactions.

• 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.

• It does not make heat by nuclear reactions

• It is (more-or-less) spherical.

• It is bigger than 1000km in diameter

IAU Committees 2003-5: 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 22nd lunchtime: Further Modified Draft Presented

New proposal slammed even harder!

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

to consensus

Wednesday 23rd

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

Wednesday 23rd

• 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 24th : 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.

• 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

Is Pluto a Planet?What do you think?

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