the sun is a star 2
Post on 03-Apr-2018
216 Views
Preview:
TRANSCRIPT
-
7/28/2019 The sun is a star 2
1/23
19-Apr-13
IESO
The Sun is a Star
Part 1
-
7/28/2019 The sun is a star 2
2/23
Formation of theSolar System
-
7/28/2019 The sun is a star 2
3/23
3
Formation of the Solar System
The Formation of the Solar System
What properties must a planetary formation theory
explain?
1. It must explain the patterns of motion of the present solar system
(last week).
2. It must explain why planets form into 2 groups.
3. It must explain the huge existence of asteroids and comets.
4. It must allow for possible exceptions to the rules.
The theory may be able to be used on other solar systems in the Galaxy
-
7/28/2019 The sun is a star 2
4/23
4
Formation of the Solar System
The Formation of the Solar System
Evolutionary Theories
All evolutionary theories have their start with Descartesswhirlpool or vortex theory proposed in 1644.
Using Newtonian mechanics, Kant (in 1755) and thenLaplace (around 1795) modified Descartess vortex to arotating cloud of gas contracting under gravity into a disk.
The Solar Nebular Hypothesis is an example of anevolutionary theory.
-
7/28/2019 The sun is a star 2
5/23
5
Formation of the Solar System
The Formation of the Solar System
Catastrophic Theories Catastrophic theory is a theory of the formation of the solar
system that involves an unusual incident such as the collisionof the Sun with another star.
The first catastrophic theory - that a comet pulled material
from the Sun to form the planets - was proposed by Buffon in1745.
Otherclose encounter hypotheses have been proposed too.
Catastrophic origins for solar systems would be quite rare(relative to evolutionary origins) due to the unusual nature ofthe catastrophic incident.
-
7/28/2019 The sun is a star 2
6/23
6
Formation of the Solar System
Solar Nebula Hypothesis
Origin of the Solar Nebula
Galactic recycling
Most of the universe started as Hydrogen and Helium. All otherheavy elements (loosely called metals by astronomers) were
formed in stars When stars die they release much of the content into space
While this has been going on for 4.6 billion years, only 2% of all thehave been converted to metals
Evidence from other gas clouds
All new systems that we can observed formed within interstellar clouds,such as the Orion Nebula
-
7/28/2019 The sun is a star 2
7/23
7
Formation of the Solar System
Solar Nebula Hypothesis
Towards a Solar Nebula Hypothesis A supernovae shock wave likely triggered the events which led to the
birth of our solar system
The nebular cloud collapsed due the force of gravity on the cloud.But the cloud does not end up spherical (like the sun) because there
are other processes going on: HeatingThe cloud increases in temperature, converting gravitational
potential energy to kinetic energy. The sun would form in the center wheretemperatures and densities were the greatest
Spinningas the cloud shrunk in size, the rotation of the disk increases(from the conservation of angular momentum).
Flatteningas cloud starting to spin, collisions flattened the shape of thedisk in the plane perpendicular to the spin axis
-
7/28/2019 The sun is a star 2
8/23
8
Formation of the Solar System
Testing the Model
If the theory is correct, then we should see disks
around young stars
Dust disks, such as discovered around beta-
Pictoris or AU Microscopii, provide evidence that
conditions for planet formation exist around many
Sun-like stars.
-
7/28/2019 The sun is a star 2
9/23
9
Formation of the Solar System
Solar Nebula Hypothesis
The Formation of Planets As the solar nebula cooled and flattened into a disk some 200 AU in diameter,
materials began to freeze out in a process called condensation (changing froma gas to a solid or liquid).
The ingredients of the solar system consist of 4 categories (with % abundance): Hydrogen and Helium gas (98%)
Hydrogen compounds, such as water, ammonia, and methane (1.4%) Rock (0.4%)
Metals (0.2%)
Since it is too cool for H and He to condense, a vast majority of the solar nebuladid not condense
Hydrogen compounds could only condense into ices beyond the frost line, whichlay between the present-day orbits of Mars and Jupiter
-
7/28/2019 The sun is a star 2
10/23
10
Formation of the Solar System
Solar Nebula Hypothesis
Building the Terrestrial Planets In the 1940s, Weizscher showed that eddies would form in a rotating gas cloud
and that the eddies nearer the center would be smaller.
Eddies condense to form particles that grow over time in a process calledaccretion.Materials such and rock and metal (categories #3 and #4).
These accreted materials became planetesimals which in turn sweep up smaller
particles through collision and gravitational attraction. These planetesimals suffered gravitational encounters which altered their orbits
caused them to both coalesce and fragment. Only the largest planetesimals grewto be full-fledged planets.
Verification of this models is difficult and comes in the form of theoreticalevidence and computer simulations.
-
7/28/2019 The sun is a star 2
11/23
11
Formation of the Solar System
Solar Nebula Hypothesis
Building the Jovian Planets
Planetesimals should have also grown in the outer solarsystem, but would have been made of ice as well as metaland rock.
But Jovian planets are made mostly of H and He gas
The gas presumably was captured by these ice/rock/metalplanetesimals and grew into the Jovian planets of today.
-
7/28/2019 The sun is a star 2
12/23
12
Formation of the Solar System
Solar Nebula Hypothesis
A Stellar wind is the flow of nuclear particles from astar.
Some young stars exhibit strong stellar winds. If theearly Sun went through such a period, the resultingintense solar wind would have swept the inner solar
system clear of volatile (low density) elements,molecules and compounds.
The giant planets of the outer solar system would thenhave collected these outflowing gases.
-
7/28/2019 The sun is a star 2
13/23
13
Formation of the Solar System
Solar Nebula Hypothesis
An object shrinking under the force of gravity heats up.High temperatures near the newly formed Sun (protosun)
will prevent the condensation of more volatile (low
density) elements. Planets forming there will thus be made
of nonvolatile, dense material.
Farther out, the eddies are larger and the temperatures
cooler so large planets can form that are composed of
volatile elements (light gases).
-
7/28/2019 The sun is a star 2
14/23
14
Formation of the Solar System
Solar Nebula Hypothesis
Problem: The total angular momentum of the planets isknown to be greater than that of the Sun, which shouldnot occur according to conservation laws (i.e. the presentSun is spinning too slowly).
Solution: As the young Sun heated up, it ionized the gas
of the inner solar system. The Suns magnetic field then swept through the ions in the
inner solar system, causing ions to speed up.
As per Newtons third law, this transfer of energy to the ionscaused the Sun to slow its rate of rotation.
-
7/28/2019 The sun is a star 2
15/23
15
Formation of the Solar System
Solar Nebula Hypothesis
Explaining Other Clues
Over millions of years the remaining planetesimals fellonto the moons and planets causing the cratering we seetoday. This was the period ofheavy bombardment.
Comets are thought to be material that coalesced in theouter solar system from the remnants of small eddies.
The Asteroid belt formed from debris that could notcoalesce into a planet due to the gravitational influenceof Jupiter
-
7/28/2019 The sun is a star 2
16/23
16
Formation of the Solar System
Solar Nebula Hypothesis
The formation of Jovian planets and its moonsmust have resembled the formation of the solar
system. Jupiter specifically:
Moons close to Jupiter are denser and contain fewerlight elements;
Moons farther out decrease in density and increase in
heavier elements.
-
7/28/2019 The sun is a star 2
17/23
17
Formation of the Solar System
The Exceptions to the Rule
Captured Moonssatellites which go the opposite waywere likely captured. Most of these moons are small are
lie far away from the planet.
Giant impactsmay have helped form the Moon and
explain the high density of Mercury and the Pluto-Charon
system. Furthermore, the unusual tilts of Uranus and
Venus can also be explained by giant impacts.
-
7/28/2019 The sun is a star 2
18/23
18
Formation of the Solar System
Solar System Destiny
The nebular hypothesis accounts for all major features in the solarsystem
It does not account foreverything, however
It probably took about a few tens of million of years, about 1% ofthe current age of the solar system
The solar system was probably not completely predestined from thecollapse of the solar nebula, though the initial were orderly andinevitable
The final stage of accretion and giant impacts were fairly random innature and made our solar system unique
-
7/28/2019 The sun is a star 2
19/23
19
Formation of the Solar System
Radioactivity
Radioactivity Certain isotopes (elements which contain differing number of
neutrons) are not stable and will decay into two or more lighter
elements
The time it takes for half of a given isotope to decay is calledthe half-life
By noting what percentage a rock (or human body) has left of a
radioactive element can enable us to estimate the age of that
object. This process is called radioactive dating. SeeMathematical Insight 8.1
-
7/28/2019 The sun is a star 2
20/23
20
Formation of the Solar System
Radioactivity
Radioactivity - examples Potassium-40 decays into Argon-40 with a half-life of 1.25 billion years
Since Argon-40 is an inert gas, it is very unlikely to have formed inside a rock
as the solar nebula condensed, so it must have formed via decay
Uranium-238, after a series ofdecays, turns into Lead-206 with half-life of
4.5 billion years Lead and Uranium have very different chemical behaviors
Some minerals have nearly no lead to begin with, so when uranium is mixed
with lead, we can assume that the lead formed via decay
-
7/28/2019 The sun is a star 2
21/23
21
Formation of the Solar System
Radioactivity
RadioactivityThe general formula for the age of a radioactive material is
(see Mathematical Insight 8.1):
10
10
log
1log
2
half
current amount
original amount
t t
-
7/28/2019 The sun is a star 2
22/23
22
Formation of the Solar System
Radioactivity
Earth rocks, Moon rocks, and meteorites The oldest Earth rocks date back to 4 billion years and some
small grains go back to 4.4 billion years. Moon rock brought
back from the Apollo mission date as far back as 4.4 billion
years. These tell us when the rock solidified, not when the planet formed
The oldest meteorites, which likely come form asteroids, are
dated at 4.55 billion years, marking the time of the accretion of
the solar system
-
7/28/2019 The sun is a star 2
23/23
The End
top related