Dwarf planets and small

solar system bodies

NVR mini-symposium

Dwarf planets,

28 October 2015,

Paul Wesselius

Topics described

• Sun and 8 planets

• Dwarf planets

• Asteroids

• Comets

• Oort cloud

• Kuiper belt

• Heliosphere

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Literature, websites • At the Edge of the Solar System (ESS): Icy New Worlds

Unveiled, Alain Doressoundiram, Emmanuel Lellouch, Springer Praxis Books, Berlijn, 2009

• Small Bodies in Planetary Systems (Lecture Notes in Physics), Editors: Ingrid Mann, Akiko Nakamura, and Tadashi Mukai, Springer, Berlijn, 2009

• A website from Jewitt, the discoverer of the first Kuiper Belt object after Pluto: http://www2.ess.ucla.edu/~jewitt/kb.html

• Belgian site with many pictures: http://www.spacepage.be/artikelen/het-zonnestelsel/dwergplaneten-en-plutoiden

• A site on dwarf planets from Mike Brown: http://www.mikebrownsplanets.com/

• The mission to Pluto: http://www.nasa.gov/mission_pages/newhorizons

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4 http://www.slideshare.net/redcedarmedia/the-sun-the-earth-the-moon

5 http://csep10.phys.utk.edu/astr161/lect/solarsys/revolution.html

6 http://csep10.phys.utk.edu/astr161/lect/solarsys/revolution.html

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Sideview of the planetary orbits, see: http://csep10.phys.utk.edu/astr161/lect/solarsys/revolution.html

Dwarf planets Resolution B5 of the IAU* • A planet is a celestial body that

1. is in orbit around the Sun,

2. has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape,

3. has cleared the neighborhood around its orbit.

• A "dwarf planet" is a celestial body that – has the properties 1. and 2. of planets, but

– has not cleared the neighborhood around its orbit, and

– is not a satellite (‘moon’)

• All other objects, except satellites, orbiting the Sun shall be referred to collectively as "Small Solar System Bodies"

8 * IAU = International Astronomical Union

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5 dwarf planets have been recognised so far by the IAU, http://app.plutosafari.com/articles/guide/definition.html

Asteroid Belt

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Between Mars and Jupiter there exists a belt of asteroids (from 2.1 to 3.3 AU*). In the stable Lagrange points of the Jupiter-Sun system there are ‘trapped’ asteroids: The Trojans and the Greeks. 750.000 larger than 1 km, 200 bigger than 100 km diameter. From: Wikipedia

* 1 AU is the distance between the Sun and the Earth = 150 million km

Near-earth asteroids

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Some asteroids can come close to the Earth and even hit it. http://astronomy.swin.edu.au/cosmos/N/Near+Earth+Asteroids

Tsjeljabinsk fireball

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On 15 Feb 2013 a fireball appeared, brighter than the Sun. Detonation energy exceeded the Hiroshima bomb (15 kiloton) energy by a factor 30 all windows were shattered. Happily such explosions occur at heights of ~ 8 km.

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Asteroids and comets visited by spacecraft, March 2015 (via: https://www.reddit.com/user/Tanchistu ). Vesta and Ceres are too large for this picture)

Ceres

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Ceres, the only asteroid promoted to dwarf planet status, seen by Dawn on 19 Feb 2015. Sebastiaan de Vet will tell much more about it, and about Vesta, also visited by Dawn.

15 http://www.wisegeek.org/what-is-the-difference-between-a-comet-and-a-meteor.htm#

A comet 1 to 50 km nucleus

67P/Churyumov-Gerasimenko

16 http://sci.esa.int/rosetta/14615-comet-67p/

On 12 Nov 2014 Philae (launched from the ESA satellite Rosetta) landed on comet 67P. The surface is very hard. That caused Philae to rebound and hop around. 67P seems to exist out of two loosely connected parts

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The dashed path is the orbit the comet would follow if it had no Jupiter encounter. The solid line show the new, smaller elliptical comet orbit after a close gravitational encounter with Jupiter. These comets are assumed to originate in the Kuiper Belt, periods < 200 years. http://www.astronomy.ohio-state.edu/~pogge/Ast161/Unit4/dance.html

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https://lcogt.net/education/article/background-asteroids-comets-and-neos/

Most newly discovered comets are long period comets. These originate from a region called the Oort Cloud which extends to about 50,000 AU from the Sun. The comets from this cloud have very elongated orbits, and therefore spend most of their time far from the Sun.

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https://lcogt.net/education/article/background-asteroids-comets-and-neos/

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The Kuiper Belt (also: Kuiper-Edgeworth Belt) is a disk-shaped region past the orbit of Neptune. It extends from the orbit of Neptune (30 AU) out to around 50 AU from the Sun and contains hundreds of millions of small icy bodies. http://theplanets.org/kuiper-belt/ . Michael Müller tells more.

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The ‘Astronomy Picture of the Day’, 14 September 2015: a digital composite picture of Pluto, made by the NASA satellite New Horizons. http://apod.nasa.gov/apod/ap150914.html

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23 http://www.ieap.uni-kiel.de/et/en/ag-heber/forschung/sun-helio.php

Bow shock lies at 110 to 160 AU. Oort cloud lies much farther out.

The Heliosphere