the terrestrial planets aim of this course - le
TRANSCRIPT
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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