Transcript Earth has formed in our solar system

Earth has formed in our solar
system
 We need to understand planetary
formation
Constraints:
• Astronomical observations
• Study of meteorites
• Study of planets
• Theoretical modelling
Planetary orbits are nearly circular
Compositional classes
Inner or terrestrial planets
Small,dense, slow rotation, few moons
Giant or jovian planets
Large, low density, fast rotation, numerous satellites
Ancient planetary surfaces are covered with impact craters
Moon
Mars
Stellar nebula
Solar nebula hypothesis
• Proposed by Kant and Laplace
• Gravitational collapse of a gaseous cloud
(supernova?)
• During collapse, faster spin (conservation of
angular momentum) and temperature
increase
• Competing forces induce flattening
• Temperature depends on location in nebula
because of cooling
• Hence location is important for planetary
composition (planets closer to the sun
should be more refractory)
• Interaction of large body at final stages
could change composition considerably
All stars form from clouds of gas and dust which roam our
galaxy. Eventually, gravity causes the cloud to collapse; since the
cloud is spinning, material falls in along the "poles" faster than it
does near the "equator". This flattening results in a disk-like
object.
Material slowly makes its way into the center of this disk,
forming a new star. While the star continues to grow, lumps
form (solar nebula is heterogeneous) in the disk which will
ultimately become planets.
The disk eventually thins as more material falls onto the star and
the protoplanets. A hole in the disk near the star forms as
material is completely incorporated into the star and planets.
Now fully formed planets exist within the hole, even as new
planets are still under construction in the outer parts of the disk.
• This stage of planetary formation is very
violent: impacts of large objects shape the
final planets (e.g. formation of the moon)
• There are many collisions and core
formation provide enough heat to melt the
planet  magma ocean
John Chambers
Ultimately, the remaining dust clears completely, leaving a
fully formed solar system like our own.
Time frame for the formation of our solar system
Stevenson, Nature, 2008
Stevenson 2008
Problems with solar nebula model
• Too little angular momentum in the centre
(sun)
• Planets in the wrong place
• Deviations from ecliptic plane
Unknowns
• How dense was the solar nebula
• Time scales
• (fast  homogeneous  differentiation)
(slow  differentiated bodies)
• Temperature
• Planetary rearrangement after initial
formation
• Volatiles