Transcript Ch. 4 review

Ch. 4 – Formation of the Solar System
• 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.
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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 (which also create the
heavier elements, including radioactive elements)
Solar Prominence – photo by SOHO spacecraft
The solar
wind expels
some heavy
elements
into space.
from the
Astronomy
Picture of
the Day site
Helium Shell Burning
on the Horizontal Branch
prior to the formation of
a planetary nebula.
Planetary Nebulae form when the core can’t reach
600 million K, the minimum needed for carbon burning.
Another dramatic result of stellar evolution:
a supernova remnant which expels heavy elements into space.
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 from interstellar material?
Young Stars
in Orion
This photo
shows the
nebula in
visible light.
Young Stars in
Orion
An 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 a
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 during 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.
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 is the protoplanetary
disk, also called a “proplyd.”
This process explains the
fact that all the objects
tend to rotate in the same
way (or ‘sense’) in a system.
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)
Ch. 5 - Exoplanets
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Planets have been discovered orbiting other stars.
Evidence from several sources:
- Distortion of protoplanetary disks (proplyds).
- Doppler shift of the light of the star, indicating radial
velocity shifts.
• - Astrometry to measure stellar wobble.
• - Detection of dimming of the star, indicating a transit
by a planet. (Most of them are found this way.)
• Over 1800 exoplanets have been found.
Beta
Pictoris
has a
planet
Extra-solar Planets are
revealed by the Doppler
effect, seen when we
study the central star
Experimental methods have their own particular bias.
Doppler surveys find only the large planets.
Kepler transit studies have only found short period planets.
Kepler has found many planets smaller than Jupiter,
so it is adding to the list of smaller planets that Doppler
measurements have not seen.
Earth-size planets with temperatures suitable for life
have been found by the Kepler spacecraft.