Transcript Our local neighbourhood – The Solar System (PPT file, 6.12 MB)

Our local
neighbourhood - The
Solar System
Dr Nicola Loaring
SALT/SAAO
[email protected]
Concept: The Scale
of our Solar System
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If the Sun were a grapefruit (10cm)
Earth, grain of sand
1mm,
15 m away
Jupiter, marble
1.5cm, 80 m away
Pluto, tiny grain of sand 0.2mm, 700 m away
And the NEXT CLOSEST sun (or star) would be in ... Nairobi !
DEMO
Concept: Two types
of Planet

Terrestrial planets:


Rocky with molten cores
Jovian planets:

Mainly gas and liquid with rocky
cores
Rocky Planets
The rocky worlds are
the 4 inner planets
plus our Moon
They have a solid rock
surface with an iron core
and a weak or no
Gas Giants
There are 4 gas giant
planets in our solar
system.
These planets
have NO solid
surfaces – just gas
and clouds that get
denser as you
move to their
centre.
Relative distribution of the two types
of Planets
Gas giant worlds are far
from the Sun
Wikipedia
Rocky
worlds
are close
to the Sun
Relative sizes
Gas giant worlds
are much larger
than rocky worlds
Jupiter – largest gas giant world
Earth – largest rocky world
NASA/JPL
Activity opportunity:
Powers of 10
Body
Radius
Surface
Area
Earth
1
1
Jupiter
Sun
10x
[101]
100x
100x
[102]
10,000x
Volume
1
1000x
[103]
1,000,000
x
Relative numbers of rings and moons
www.hubblesite.org
Gas Giant worlds have rings
and many moons.
(From left to right: Enceladus and shadow, Dione and
shadow. Titan and Mimas are off the limb to the right).
Rocky worlds have no
rings and no, or few,
moons.
Why are there two types of
planet?
Solar System Formation


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


All orbits are in the same direction
and in the same plane.
Suggests a common origin.
Solar system formed when a cloud
of gas and dust in space was
disturbed. Gas and dust drawn
together, forming a solar nebula.
The cloud began to spin as it
collapsed and therefore flattened.
As the disk got thinner particles
formed clumps, planetisimals
eventually forming planets or
moons.
As the cloud continued to fall in, the
centre eventually got so hot that it
became a star, the Sun. Solar wind
then blew away excess material.
Why are there 2 types of
planet?
Inside the frost line: Too hot for
hydrogen compounds to form
ices.
Outside the frost line: Cold
enough for ices to form.
Inner parts of disk are hotter than outer parts. Only materials that solidify at high temperatures can
condense to form solid particles. Rock can be solid at much higher temperatures than ice.
DEMO Density

and Composition
Earth 5.5 g/cm3 composition- iron, rock
Saturn 0.7 g/cm3 composition- some rock,
volatiles and lots H & He

Callisto 1.9 g/cm3, Titan 2 g/cm3 composition -rock
and ice

Asteroids and Comets
Leftovers from the accretion process
Rocky asteroids inside frost line
Icy comets outside frost line



The inner rocky PlanetsMercury
Has the largest temperature
extreme in the solar system from 183C to 430C.
Second densest planet after the
Earth, so must have a large iron
core.
Has a very thin atmosphere
consisting of atoms blasted off its
surface from the solar wind.
Atmosphere is constantly being
replenished.


DEMO
Heavily cratered surface because
its atmosphere is so thin.
Mission
Launch Year
Mariner 10
1973
Messenger
2004 (to orbit 2011)
BepiColombo
2013 (to arrive 2019)
The inner rocky Planets Venus
Recent Missions
Launch Year
Galileo
1989 (flyby 1990)
Magellan
1989 (in orbit 1990-1994)
Cassini
1997 (flyby 1998, 1999)
Venus Express
2005 (arrive 2006)
Messenger
2004 (flyby 2006, 2007)
Planet C
2010
Venus is a similar size to the Earth.
It atmosphere is mainly Carbon dioxide and Nitrogen.
Its very hot there due to the ‘Green house effect’ a whopping 462C.
Our home the Earth
Earth is at a distance of 150 million
kilometres from the Sun. Sunlight takes 8
minutes to reach us.
Our atmosphere is composed of 78 percent
nitrogen, 21 percent oxygen and 1 percent
other constituents.
71% of the Earth’s surface is covered by
water!
Earth is the only planet in the solar system
known to harbour life.
Picture taken by Apollo 17 astronauts
Mission
The Moon
Launch Year
Apollo manned missions
1968 - 1972
Lunar Prospector
1998
SMART-1
2003
SELENE (JAXA)
2007
Chandrayaan-1
2008
LRO
LCROSS
Heavily cratered.
2009
Evidence for water.
2009
The inner rocky Planets Mars
Mars is 1/10th the mass of Earth
Average temp is –63C
Rock are made of silicates (like sand) and also
a dash of iron oxides to give it that reddish
colour (Mars is rusty!)
Surface is dry now, but scientists believe there
were once rivers, lake and maybe oceans of
water
Water exists in “permafrost” a few metres
below the surface (Mars Express / Mars
Odyssey). Maybe even liquid water down
there! (MGS).
No landers have detected water in soil, but
have found evidence of past water.
Recent Missions
Mars
Viking 1
Mars has the
Viking 2
highest (extinct)
Mars Global Surveyor
volcano in the
Mars Pathfinder
Solar System:
Mars Express
Olympus Mons at
Spirit / Opportunity
24 km high 2.7
Phoenix
times Everest!
Launch Year
1975 (landed 1976)

1975 (landed 1976)
1996 (arrived 1997)
1996 (arrived 1997)
2003 (still active)
2003 (still active)
2007 (till 2008)
ExoMars
2016?
Mars Sample Return Mission
2020?
The gas giants -Jupiter
Mission
Largest planet in the solar system
– its diameter
is 11x the Earth’s diameter.
Jupiter takes about 12 years to orbit the sun and
rotates in about 10 hours.Pioneer 11
Jupiter is a ball of dense hydrogen, helium,
water, nitrogen and other gases over a rocky
core. ~90% H, ~10% He.
Voyager 1
Launch
1974 (arrived 1979)
1977 (arrived 1980)
Above core is the main bulk of the planet which
is liquid metallic hydrogen. (Huge pressure).
Ionized protons and electrons in liquid form.
Voyager 2
Powerful winds, jet streams, lightning and huge
hurricane-like storms like the Great Red Spot.
This storm has been raging for over 300 years
Galileo
and is twice the size of Earth!
1977 (arrived 1981)
1989 (arrived 1990, still operational)
Cassini and Saturn
Mission
Pioneer 11
Voyager 1
Launch Date
95 times the Earth’s mass.
Saturn, famous for its rings. These
are made up of trillions of icy
1973 (flyby 1979)
particles.
1015 tons of material in the rings,
enough for a small moon!
1977 (encounter 1980)
No more than 50 million years old
(MUCH younger than the planet) continually replenished
2 outer portion of the C ring 1977
This image shows, from leftVoyager
to right, the
and (encounter 1981)
inner portion of the B ring. The B ring begins a little more than halfway
across the image. The general pattern is from "dirty" particles indicated by
red to cleaner ice particles shown in turquoise in the outer parts of the
rings.
1997 (orbiting 2004, Titan descent
Cassini-Huygens
2005 - orbiter still operational)
Titan
Titan's surface in
2004-2005!
Liquid ethane/methane on surface
Lots of hydrocarbons
Uranus
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Primarily composed of rock
and ices with only 15% H
(much less than Jupiter and
Saturn).
Mission
No rocky core like Jupiter and
Saturn, but material is more
evenly distributed.
Voyager 2
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No liquid metallic hydrogen
envelope.
Atmosphere of 83% H, 15%
He, 2% methane.
Launch Date
1977 (encounter 1985-1986)
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Composed of ices and rock with
about 15% H and a little He
Neptune
Atmosphere mainly H and He with
a little methane which gives it its
blue colour as methane absorbs
Mission
red light
Small solid core, the size of the
Earth
Voyager 2
No distinct layers like Uranus
(unlike Saturn and Jupiter)
Neptune has the fastest winds in
the solar system reaching 2000
Launch Date
1977 (flyby 1989)
What Counts as a Planet?
The IAU definition of a planet (2006):

is in orbit
around
the
Sun,
Mission

has sufficient mass so that it is nearly round

Launch
has "cleared the neighborhood" around its orbit.
New Horizons
2006 (to arrive 2015)
Dwarf Planets
The IAU currently recognises five dwarf planets—Ceres, Pluto, Haumea, Makemake,
and Eris.
Ceres is in the asteroid belt others in the Kuiper belt.
Many Kuiper Belt objects, exist in what is believed to be a vast shell of icy and rocky
objects that live at the very edge of our solar system.