Transcript Day 9 - Ch. 4 -

Ch. 4 – Formation of the Solar System
and other Planetary Systems
• Stars produce the heavier elements.
• Formation of the Solar System (stardust,
gravity, rotation, heat, and collisions).
• Comparative Planetology (characteristics of
the planets of the solar system).
• Debris and remnants in the solar system.
• Extrasolar planets (outside the solar system).
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The heavy elements in the solar system were
formed in an earlier generation of stars
The early Universe contained only hydrogen, helium,
and traces of lithium.
All heavier elements were created in the core of stars
as they “burned” the hydrogen and helium into carbon,
oxygen, neon, calcium, magnesium, silicon, and iron
These were then expelled into space by
- stellar winds (happening with our sun now)
- planetary nebulae (not planets, but similar appearance
to early astronomers) - see slides
- nova and supernova explosions
Solar Prominence – photo by SOHO spacecraft
from the
Astronomy
Picture of
the Day site
link
Helium Shell Burning
on the Horizontal Branch
A G-Type Star is similar
to our Sun.
The evolution is shown
during an imaginary
trek through space.
At the end of the
red giant stage,
the core is small,
the envelope huge,
and the outcome
depends on the
total mass of the star.
Planetary Nebulae form when the core can’t reach
600 million K, the minimum needed for carbon burning.
A Planetary Nebula shaped like a sphere, about
1.5 pc across. The white dwarf is in the center.
A Planetary Nebula with the shape of a ring,
0.5 pc across, called the “Ring Nebula”.
Cat’s Eye Nebula, 0.1 pc across, may be from
a pair of binary stars that both shed envelopes.
M2-9 has twin lobes leaving the central star
at 300 km/sec, reaching 0.5 pc end-to-end.
A Nova is an
explosion on a white
dwarf, but only a
small amount of
material on the
surface of the
white dwarf explodes.
Nova Herculis 1934
a) in March 1935
b) in May 1935,
after brightening
by a factor of
60,000
Nova Persei - matter ejection seen 50 years after
the 1901 flash (it brightened by a factor of 40,000)
Another dramatic result of stellar evolution:
a supernova remnant which expels heavy elements into space.
The Solar System
Dark Dust
Clouds:
not just
an absence
of stars!
A Dark Cloud: dust and gas, dense enough to block starlight.
Radio Emission reveals the dark dust cloud.
Horsehead
Nebula
(The neck
is about
0.25 pc
across)
A nice
example
of a
dark dust
cloud
Formation
of the
Solar
System
There are several kinds of objects in our Solar System
Terrestrial planets: Mercury, Venus, Earth, and Mars
Jovians: the “gas giants” Jupiter, Saturn, Uranus, and Neptune
“debris” – asteroids, comets and meteoroids, and some objects
still being classified: Kuiper Belt, Oort cloud
How did these form?
Young Stars are
forming in Orion
top: visible photo
shows the nebula
bottom: IR photo
shows the stars
more clearly,
note the four central
stars (the Trapezium)
see next slides
Young Stars
in Orion
visible photo
shows the
nebula
Young Stars in
Orion
IR photo shows
the stars clearly,
note the four
central stars
(the Trapezium)
Orion Nebula,
A closer look
reveals “knots”
or “evaporating
gaseous globules”
EGGs, some
of which may
contain protostars.
These globules
may contain
evolving planets
as well as the
central protostar.
Several disks
that may be
protoplanetary
disks are found
after blowing up
the Hubble photo.
Major facts that any theory of solar-system formation must explain
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Each planet is relatively isolated in space.
The orbits of the planets are nearly circular.
The orbits of the planets all lie in nearly the same plane.
Direction of planet’s movement in orbit is same as sun’s rotation.
Direction of planet’s rotation is same as sun’s rotation. (*usually*)
Direction of the various moon’s revolution is same as planet’s
rotation.
The planetary system is highly differentiated.
Asteroids are very old, and not similar to terrestrial planets or
Jovian planets.
The Kuiper belt is a group of asteroid-sized icy bodies orbiting
outside the orbit of Neptune. (KBO – Kuiper Belt Objects)
The Oort Cloud is composed of icy cometary objects that do not
orbit in the same plane as the planets (the ecliptic).
Angular Momentum influences the formation of
planetary disks in the collapse of a cloud of gas
Beta Pictoris is one
example of a
protoplanetary disk
top: false color image with the
central star blocked out
to show the disk
bottom: artist’s rendition
of what the disk might look
like if a planet is forming
Beta Pictoris
has a
protoplanetary
disk
and
a planet !
Image from ESO
Conservation of Angular Momentum
Conservation of Angular Momentum in a figure skater.
(demo)
A Theory of
Solar System Formation:
a spinning gas cloud
condenses to a much smaller
size, and begins to rotate
much faster due to
conservation of angular
momentum.
This was the protoplanetary
disk, also called a “proplyd.”
This process explains the
fact that all the objects
tend to rotate (CCW) in
the same way (or ‘sense’).
Jovian Condensation: due to whirlpools? Or accretion?
Differentiation may be due to
the temperatures in the
Early Solar Nebula
The inner solar system is
closer to the early Sun, and so
it is hotter. Volatile gases are
not condensed on the planets
and end up condensing in the
Jovian planets further out.
This is similar to a process in
chemical plants called
distillation or fractionation.
Sun and Planets (approximate scale of diameters)
The Inner Solar System (sizes NOT to scale) link
The Scale of the Solar System
To appreciate the scale of the solar system, it is
useful to make a scale model.
There is a spreadsheet-like form to make your
own scale model of the solar system at
http://www.exploratorium.edu/ronh/solar_system/index.html
Extrasolar planets
• Planets have been discovered orbiting other stars.
• See the PowerPoint file “day09exo.ppt” for the slides
on this topic.