Formation of the Formation of the Solar SystemSolar System

Formation of the Solar System

From interstellar cloud to planetary system

Formation of the Solar Nebula

Self gravity begins to _________ the cloud

As the cloud gets smaller, it begins to rotate faster, due to ______________ ________________.

Centripetal force prevents gas from collapsing in the plane of rotation

Gas falling from the top collides with gas falling from the bottom and sticks together in the ecliptic plane

In a large, slowly rotating cloud of cold gas

conservation of

collapse

angular momentum

Formation of the Solar Nebula

The densest region of the disk (the center) becomes the _____. Eventually, fusion in the Sun occurs.

Atoms orbiting in the disk bump together and form molecules, such as water. Droplets of these molecules stick together to form ______________.

Over time, the planetesimals grow as more molecules ________ out of the nebula

In the flat ____________ solar nebula

Sun

planetesimals

condense

Formation of the Solar Nebula

Differential rotation (due to Kepler’s laws) will cause particles in similar orbits to eventually meet up. One will _______ the other, forming a bigger body.

The bigger the body, the greater its gravitational force, and the more attraction it has for other bodies. Further accretion will occur. ___________ form.

Planetesimals grow …

accrete

Protoplanets

Formation of the Solar Nebula

While protoplanets are forming, the Sun’s luminosity is growing, first due to gravitational contraction, then due to _____________.

Regions of the nebula close to the Sun will get hot; the outer regions will stay cool. In the hot regions, light elements will __________; only heavy elements will condense out of the nebula

Material begins to evaporate

nuclear ignition

evaporate

Radiation Pressure and the Solar WindTwo other processes are also important for driving light gases from the inner part of the solar system.

_______________: Photons act like particles and push whatever particles and dust they run into.

_________: The Sun constantly ejects (a little) hydrogen and helium into space. This solar wind pushes whatever gas and dust it runs into.

Radiation pressure

Solar wind

The Pre-Main Sequence Sun

As the Sun formed, it generated a lot of energy via _____________________. During this time, it was brighter than it is today. The radiation pressure in the inner solar system was greater.

In addition, due to conservation of angular momentum, the young Sun was also spinning faster than it is today. This caused the solar wind to be stronger.

gravitational contraction

Accretion Once the major bodies of the solar system were formed, most of the remaining debris was either ejected out of the solar system or accreted onto other bodies by gravitational encounters.

Differentiation

Early in the history of the solar system, planets would be molten due to

Continuous accretion of left over material from the solar system formation.

Energy from the fission of radioactive isotopes.

Observations of Protostellar Disks

The solar nebula theory states that young stars should be surrounded by a disk consisting of molecular gas and dust. These are now being observed.

The Age of the Solar System

We can estimate the age of the Solar System by looking at _________________. These are unstable forms of elements that produce energy by splitting apart.

The radioactivity of an isotope is characterized by its ____ ___ – the time it takes for half of the ______ to decay into its ________ element. By measuring the ratio of the parent to daughter, one can estimate how long the material has been around.

radioactive isotopes

parentdaughter

half-life

Radioactive Elements

Isotope#

protons#

neutrons

Daughter Half-life (years)

Rubidium-87 37 50 Strontium-8747,000,000,000

Uranium-238 92 146 Lead-206 4,510,000,000

Uranium-235 92 143 Lead-207 710,000,000

Potassium-40 19 21 Argon-40 1,280,000,000

Aluminum-26 13 13Magnesium-26

730,000

Carbon-14 6 8 Nitrogen-14 5,730

Each of these isotopes spontaneously decays into its daughter. In each case, the daughter weighs less than the parent – energy is produced.

Age of the Solar System

When rocks are molten, heavier elements (such as uranium) will separate out from other elements. (In liquids, dense things sink, light things rise.) Once the rocks solidify, radioactive decay will then take over.

• On earth, the oldest rocks have ages of __ billion years

• The oldest asteroids have ages of ____ billion years• Rocks from the “plains” on the Moon have ages of

about 3 billion years. The oldest Moon rocks have ages of 4.5 billion years.

The solar system is therefore 4.5 billion years old.

3

4.5

http://www.astro.psu.edu/users/rbc/a1/340,1,Slide 1