AST101: The Sun and its Neighbours
Class 2: A Pictorial View of our Solar System
Professor Jeremy Webb
A Pictorial Tour of our
Solar System
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Learning Goals
• How can we describe the shape and motion of
objects in the solar system?
• How are the patterns of motion in the solar
system related to how it is formed?
• What is the difference between a terrestrial
and a Jovian planet?
• What are some facts about our solar system
planets?
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A solar system consists of a star orbited
by planets, moons, and lots of debris
(comets, asteroids, dust)*
* “Solar System” or “The Solar System” means our solar system; “solar system”
or “star system” can be any such system.
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Our Solar System is HUGE and
the vast majority of it is
empty.*
*It’s not quite empty—tiny, tiny quantities of gas and dust
fill the space
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Our Solar System
(image credit: NASA)
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The Inner Solar System:
Mercury, Venus, Earth, and Mars
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The Outer Solar System:
Jupiter, Saturn, Uranus, Neptune, many
dwarf planets & comets
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What do you think?
• In addition to their orbit, inner and outer
planets also differ by their:
– A) Composition
– B) Size
– C) Atmospheres
– D) All of the above
– E) What is an atmosphere?
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Terrestrial =
Earth-like
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Terrestrial planets –
small, rocky, thin or no
atmosphere, few moons,
made of heavy elements
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Mercury
Earth
NASA / © Calvin J. Hamilton
Venus
Mars
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Jovian =
Jupiter-like
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Jovian planets –
large, liquid + gas, small
rocky core, many moons,
made of light elements
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“gas giants”
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Saturn
Uranus
NASA / © Damien Peach
Jupiter
Neptune
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What do you think?
• How many planet Earth’s could fit inside
Jupiter?
– A) 10
– B) 100
– C) 1000
– D) 10,000
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Inner Planets
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Mercury
• No atmosphere, highly cratered surface
• Rocky exterior with a huge iron core
• Temperature fluctuates between -170 C
and 425 C (lead melts at 327 C)
• No moons
• Only two probes have ever been sent to Mercury:
– Mariner 10 (1974-1975)
– MESSENGER (2011-2015)
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NASA
Images of Mercury from MESSENGER
(both images are in false colour).
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Credit: MESSENGER
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Credit: MESSENGER
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Venus
• Thick CO2 atmosphere,
lots of possibly active volcanoes
• About the same size as Earth
• Runaway greenhouse effect makes it even hotter
than Mercury: 460 C everywhere all the time (lead
melts at 327 C)
• Rains acid
• No moons
• Rotates very slowly and backwards!
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Magellan (1991) radar map sees through the clouds
NASA
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Earth
• Wet planet covered in creepy-crawlies
• Unusually big moon
• Only planet we have to live on. Probably
shouldn’t wreck the place, huh?
+ way too much CO2
à
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Mars
• Very thin CO2 atmosphere
• Many huge, extinct volcanoes
• Was probably Earth-like in the distant past
(i.e. wet & warmish)
• Many surface features appear to have been carved by
water
• Lots of sub-surface water
• No life known to date
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Credit: NASA/JPL
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Olympus Mons
Credits: NASA; © 2004 Wolfgang Weiser ; Wikipedia user Resident Mario ;
ESA / DLR / FU Berlin (G. Neukum)
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Valles Marineris
Credit: NASA / R. Kline; ESA / DLR / FU Berlin (G. Neukum)
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NASA: Spirit and Opportunity (2004- )
• Spirit stopped
working in 2011
• Opportunity was
still going (43 km
and counting …)
until we lost contact
with it in 2018 L
Credit: NASA/JPL-Caltech/Cornell/MAAS Digital LLC
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Lots of Evidence That Mars Was Once Wet
Credit: © 2014 Pearson Education, Inc.
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NASA: Perseverance Rover
• Looking for signs
of ancient life
• Collecting rock
and soil samples
– Potentially for
return flight
home!
• Brought a
helicopter with it!
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NASA: Ingenuity Helicopter
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Asteroid Belt
• In between orbits of Mars and Jupiter
• Many thousands or millions of
“rubble piles”
• Material left over from the formation of the
solar system, prevented from turning into a
planet by tides from Jupiter
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False colour image of asteroid
Gaspra captured by the Galileo
spacecraft (NASA).
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Asteroid 433 Eros, as seen by the
NEAR spacecraft in 2000
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NEAR actually landed
on Eros
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Outer Planets
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Jupiter
• Largest planet in the solar system
• Thick gaseous atmosphere surrounds a giant ball of
liquid hydrogen
• > Earth-sized rock somewhere deep inside?
• Has very faint rings
• Many moons: more than 60 known to date
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True colour image of Jupiter
from the Cassini spacecraft
(NASA)
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Juno was launched by
NASA in 2011, and
arrived at Jupiter on July
5, 2016
Image credit: NASA/JPL
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Io is the most volcanically active body in the solar system,
thanks to tides from Jupiter.
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Eruption of the Tvashtar volcano on Io as seen by
the New Horizons spacecraft on its way to Pluto.
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Saturn
• A real gas giant – it’s mostly gas
• Spectacular rings
• Also more than 60 known moons
• Cassini spacecraft is there now, taking
gorgeous pictures
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Image Credit: NASA/JPL-Caltech/Space Science Institute
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Image Credit: NASA/JPL-Caltech/Space Science Institute
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The rings of Saturn are made of tiny
particles of mainly ice (artist’s
conception)
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Uranus and Neptune
• Like gas giants, but these two are principally a
slushy ice mixture à “ice giants” ?
• Both about the same size
• Both bluey/green
• Both have many moons
• Both have faint rings
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Uranus, as seen by
Voyager 2
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direction
to Sun
Uranus is tipped over!
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Neptune, as seen by
Voyager 2
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Beyond Neptune
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Trans-Neptunian Objects
• Beyond Neptune, there are many dwarf planets
• These are small, icy bodies
• Pluto is the largest one known
• They take a long time to orbit the Sun
• New Horizons has recently given us our first-ever close
up view of a trans-Neptunian object
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The best picture we had of Pluto until 2017, using lots of
computer enhancement.
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New Horizons was
launched on 19 January
2006, swung by Jupiter
and took 6 months of
‘flyby’ footage of Pluto
and its moons in 2015.
Credit: NASA
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Credit: NASA
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The Kuiper Belt is a
ring of comets
orbiting just beyond
Neptune.
This is debris left
over from the
formation of the
solar system.
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The Oort cloud is a spherical cloud of perhaps a
trillion comets surrounding the solar system.
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Rosetta, the mission to comet
https://petapixel.com/2019/09/09/this-video-was-made-from400000-actual-photos-of-a-comet-in-space/
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‘Oumuamua is an interstellar asteroid that flew
through the solar system at an accelerated rate
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Learning Goals
• How can we describe the shape and motion of objects
in the solar system?
– Except comets, most things have near circular orbits and
are often rotating
• How are the patterns of motion in the solar system
related to how it is formed?
– Most things orbit and rotate in the same direction
• What is the difference between a terrestrial and a
Jovian planet?
– Distance from Sun, chemical composition, size, mass,…..
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