Download The Solar Nebula Theory

Odds and Ends – the Solar
Nebula Theory
Summing Up
SNT Explaining the Solar System
• The Solar System’s disk shape
– Inherited from the motion of materials in the solar
nebula.
– The planets and moons mostly rotate and revolve
in the same directions because they evolved from
the same gas cloud.
– The planet’s orbits lie in the same plane because
the solar nebula collapsed into a rotating disk
from which the planets were formed.
SNT Is Evolutionary
• The SNT is mostly evolutionary – it uses
continuing processes (processes we observe in
our own SS and other star systems) to
describe how planets were gradually built.
The SNT and Catastrophic Events
• The SNT does turn to catastrophism to explain
certain things such as the rotation of Uranus.
• It is hypothesized that Uranus rotates on its
side because of an “off-centered collision with
a massive planetesimal when the planet was
newly formed.”
Division between Jovian and Terrestrial
Worlds
• This can be understood by differences in the
condensation sequence.
– Terrestrial planets formed in the inner part of the
solar nebula with higher temperatures, which
meant that the materials were solid, high density,
particles like metals and silicates.
– Jovian planets formed in the outer nebula with
lower temperatures (beyond the frost line), which
allowed gases to form large amounts of ices.
The Missing Planet
• The SNT predicts a planet between Mars and
Jupiter.
– There is no planet there but there is an asteroid
belt.
– Mathematical models indicate that the reason
asteroids are there and not a planet is that
Jupiter’s massive size disturbed the planetesimals
and they did not accrete – instead they collided at
high speeds.
Comets and Other Objects
• Comets are among the last of the
planetesimals.
– Comets have different origins but many, like ISON,
are as old as the Solar System.
• The icy Kuiper belt objects also appear to be
ancient planetesimals that formed in the
outer solar system but were never
incorporated into a planet. They have not
changed much since the SS was young.
The Jovian Satellites
• The Jovian planets have extensive “satellite
systems.”
– Some of the moons may have formed in orbit
around forming planets in a miniature version of
the sola nebula.
– The smaller moons may have been captured
asteroids or other planetesimals.
The Heat of Jupiter and Saturn
• The heat of formation for Jupiter and Saturn
was tremendous (all of the in-falling materials
would have released lots of energy).
– Jupiter would have been hot enough to glow with
a “luminosity” of about 1% of that of the present
sun.
– Fusion reactions never got going but both Jupiter
and Saturn radiate more heat than they absorb
from the sun – they are evidently still cooling.
Common Age
• The SNT has no difficulty explaining the
common ages of the solar system’s bodies.
– According to the theory, the planets, the sun, and
all of the other inhabitants of our SS should be
roughly the same age, which evidence
corroborates.
The SNT and Angular Momentum
• If the planets formed from a contracting
nebula, then the sun should have been left
spinning very rapidly.
– That is, it should have most of the angular
momentum (moment of inertia * angular velocity)
in the solar system.
– Instead, it has very little.
Lastly, what of the angular
momentum problem?
We have used
the Spitzer
Space Telescope
to tackle this
question –
peering into the
Orion Nebula.
The SNT and Angular Momentum
• To study why the sun does not spin rapidly (its
rotation is quite slow), astronomers have used
the Spitzer Telescope to examine 500 young
stars in the Orion Nebula.
– They have found that the stars that rotate slowly
are 5X more likely to have a surrounding gas and
dust disk than the faster rotators.
The SNT and Angular Momentum
– Astronomers have observed that the young, slow
rotating, stars (like our sun would have been) have
strong magnetic fields that extend out into their
disks.
– This allows the transfer of angular momentum
from the young sun to the material in the disk.
– The question of angular momentum is no longer a
problem for the SNT.
Your New Understanding
• Hopefully, your new understanding of the
solar system has given you a new way of
thinking about our solar system – and all of its
inhabitants (the sun, the planets, asteroids,
comets, etc.)
– As well as humanity, which of course includes
you
– We are as much a product of our solar system’s
formation as the planets.
What Science Is . . .
• Science is, at its core, a new way of perceiving
of the universe around you and your place in it
based on the observation of natural
phenomena.
Understanding over time will change –
it will get deeper and more complete
(we have come a long way since
Galileo).
We are still at the beginning of our
understanding.