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The Terrestrial Planets

Lecture 1: Introduction

? The Terrestrial planets at correct relative size:

Mercury Venus Earth Mars

Provide a general introduction to the four terrestrial

(Earth-like) planets (Mercury, Venus, Earth and Mars).

By the end you should be able to identify their major

features and their common or unique properties.

Aim of this course:

Course Outline

Lecture 1 Introduction

Lecture 2 Earth – interior

Lecture 3 Earth – atmosphere

Lecture 4 Venus – Earth’s twin?

Lecture 5 Mars – dead or alive?

Lecture 6 Mercury – dense and hot

Lecture 7 The Moon – properties & origin

Lecture 8 Summary & Planet Formation

Listed textbook for this course:

“Discovering the Solar System” by Barrie W. Jones

Good for detail and if doing several planet courses

Any modern introductory astronomy text – e.g.

“Astronomy Today” by Chaisson & McMillan

On-line: brief summary handout (as given out today) and

(incomplete – images and tables) copies of each lecture, at

http://www.star.le.ac.uk/pto2/planets.html

You need to take notes of text material during lectures

Course books, handouts and the WWW

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MANY web pages – some recommended examples:

http://nineplanets.org

A multimedia tour of the Solar System.

http://www.solarviews.com/eng/

Another multimedia experience.

http://exoplanet.eu

An excellent site for information on extra-solar planets.

http://www.nasm.si.edu/apollo/

Site for information on the Apollo missions to The Moon.

Jupiter 71490 km

Saturn 60270 km

Uranus 25560 km

Earth 6378 km

Neptune 24765 km

Venus 6052 km

Mars 3397 km

Ganymede 2635 km (Moon of Jupiter)

Titan 2575 km (Moon of Saturn)

Mercury 2440 km

Quiz: name the 10 largest objects in

the Solar System (excluding the Sun)

Introducing the Solar System

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What is in the Solar System?

Sun, planets, moons, asteroids, comets, dust…

Sun = 99.85% of mass Comet West Eros Dust

Planets = 0.135% of mass!

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The Planets

• The planets orbit counterclockwise in the Ecliptic plane

• Orbits are ellipses, with Sun at one focus – most with small

eccentricity (e) (orbits obey Kepler’s Laws)

• Earth orbits Sun at mean distance of one “Astronomical Unit”

• Mercury’s orbit (and Pluto) has a significant eccentricity and

inclination (angle from Ecliptic plane)

Planet Orbital

semi-major

axis (AU)

Orbital

Period

(years)

Mass

(Earths)

Diameter

(Earths)

Average Density

(kg/m³)

Mercury 0.387 0.241 0.055 0.383 5430

Venus 0.723 0.615 0.815 0.949 5240

Earth 1.000 1.000 1.000 1.000 5520

Mars 1.524 1.881 0.107 0.533 3940

Jupiter 5.203 11.86 317.83 11.21 1330

Saturn 9.555 29.42 95.16 9.45 700

Uranus 19.22 83.75 14.50 4.01 1300

Neptune 30.11 163.7 17.20 3.88 1760

Pluto 39.54 248.0 0.0025 0.180 2100

Planetary data Asteroids – interplanetary debris

• Over 100,000 known - most between Mars and

Jupiter (>100m are asteroids; rest are meteroids)

• Total mass < 0.05 x Moon. Largest is Ceres (940 km)

• Earth-crossing asteroids are of great interest!

• Source of most meterorites/meteors

Iron & Nickel –

rare, similar to

type M asteroids

Chondrite –

similar to

terrestial

mantle/crust

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NASA Near Earth Asteroid Rendezvous MissionPrincipal target: asteroid Eros

Arrived late 1998; landed Feb. 12 2001

East and West hemispheres

Size 33 x 13 x 13 km

Landing image:

Distance 250 m

Image = size of

lecture room

Big craters, grooves, then smaller

craters – get evolutionary sequence

from surface features

NASA Stardust Mission

Target: Comet Wild 2

View from 500 km – looks like an asteroid surface

Left image: short exposure - see craters, boulders etc.

Right image: long exposure - see dust jets

The Kuiper Belt and Pluto (&TNOs)

Kuiper belt: ~1010 icy objects beyond Neptune (30–1000 AU)

Pluto is a large example.

Quaoar discovered in 2002 – half the size of Pluto. Other

large objects found since (e.g. Sedna; 2003 UB313 (Eris)).

Pluto

See changes in colour over time and in mass of atmosphere.

May be due to melting/warming of nitrogen ice.

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Is Pluto a planet?

Question: Should other large objects at similar distances to

Pluto (including Pluto) also be called planets?

All are in inclined, eccentric orbits

with periods of 300-600 years.

Several have moons.Where is Eris?

Eris and DysnomiaEris is the Greek goddess of strife and discord. Her

child, Dysnomia, is the goddess of Lawlessness.

Dysnomia’s orbit allows for an accurate mass estimate: M(Eris) = 1.27 x M(Pluto)

Eris density (~2.5 kg m-3) similar to Pluto (~1.8 kg m-3) (low compared to Earth)

IAU resolutions 2006

(or, how to lose friends and influence nobody)

5A. 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".

6A. The IAU further resolves:

Pluto is a "dwarf planet" by the above definition and is recognized as the prototype of a new

category of trans-Neptunian objects.

IAU resolutions 2006

(or, how to lose friends and influence nobody)

5A. 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".

6A. The IAU further resolves:

Pluto is a "dwarf planet" by the above definition and is recognized as the prototype of a new

category of trans-Neptunian objects.

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Extends to 100,000 AU with total mass = 30 x Earth

The Oort cloud

4th October 1957 Sputnik 1 launched27th August 1962 Mariner 2 - the first

interplanetary craft flies to Venus

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20th July 1969 Apollo 11 lands on Moon 29th March 1974 Mariner 10 reaches Mercury

Messenger flyby 1,2,3:

Feb. 14 & Oct. 6 2008, Sept. 29 2009

July 1976 Viking landers touch down on Mars

No Martians seen…

20th August 1977 Voyager 2 launched

5th September 1977 Voyager 1 launched

Followed Pioneer missions (launched 1972/73) to Jupiter

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Voyager mission used “Gravitational slingshot” July 1979 Voyagers discover Volcanism on Io and

3 new moons of Jupiter

1981 Voyager 2 image of Saturn. Voyager finds 3

new moons and complex structure in the ringsJanuary 1986 Voyager 2 reaches Uranus.

Finds 10 moons and measures a magnetic field

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August 1989 Voyager 2 passes Neptune, finding 6

moons and geysers on Triton

1990-1994 Magellan maps Venus

Feb 14 1990 Voyager 1 portrait of the Solar SystemSeptember 1992 First Kuiper Belt Object discovered

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1995 First extra-solar planet discovered by

Michel Mayor and Didier Queloz

December 7th 1995 Galileo drops probe into JupiterProbe entered atmosphere at 106,000 mph (x100 rifle bullet)

15th October 1997 Cassini-Huygens mission to

Saturn launched – arrived July 2004

Saturn and Titan from 285 million km

January 2004

ESA Mars Express image of Gusev crater +

image from NASA Spirit rover

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Cassini (Saturn)

& Huygens probe (2005, Titan)

Surface image

View from 8km up

Huygens probe release into Titan

Deep Impact – Comet Tempel 1: 2005 July 4

First extra-solar planet imaged: 2008

Planet roughly x3 mass of Jupiter but orbits at a

distance of 115 AU (about x20 distance of Jupiter )

Kepler planets February 2011

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Selected MissionsMessenger (2004; arrived 2011)

Bepi-Colombo (2016; arrives

2024)

Rosetta (2004)

Venus Express (2005)

NASA mission to Mercury

ESA+Japan mission to Mercury

ESA mission to visit comets

ESA mission to Venus

Corot (France/ESA) (2006)

Kepler (NASA) (2009)

Search for extra-solar planets

New Horizons Mission (2006) NASA mission to visit Pluto

(2015) and the Kuiper belt

The End