Chapter 8 Origin Of The Solar System Flashcards
What is a circumstellar disc?
This is a swirl of material their forms around a young star. Typically as the gas cloud the star forms from collapses into a disc.
What is the Jeans mass?
This is the critical mass that a gas cloud requires for the gravitational contraction to overcome the outward pressure caused by the random movement of particles allowing it to collapse into a star.
What is cloud fragmentation?
This is a process by which a collapsing cloud fragments, with each fragment collapsing to form its own star. This is how open clusters are believed to be formed.
How does a protostar form?
As a fragmented gas cloud collapses, the gravitational energy is transferred through the mutual collisions of molecules to thermal kinetic energy and the temperature rises.
After a few thousand years of contraction the edge of the cloud could be as hot as 2000 - 3000 k.
What is bipolar outflow?
This is when gas flows out of a protostar in opposite directions, typically at high velocities (50 km/s)
What is a T tauri star?
Similar to a proto-star this is an object that looses mass through stellar winds.
What happens when a protostar turns into a proper star?
As the protostar collapses, the core heats up. Eventually the critical point is met where the core is hot enough to start nuclear fusion reactions. The energy released is enough to halt contraction and a proper star is formed.
What are the 4 key stages recognised regarding the formation of the solar system ?
1 dense dead collapse (0.1 - 0.5 MA).
2 disc dissipation, where material falling into the accretion disc is transported inwards onto the protosun (interval of 0.05 MA).
3 terminal accumulation of the sun, during which time the protosun becomes a T tauri star and planetary accretion begins (between 1-2 MA).
4 gas dissipation where planetary accretion in the inner solar system ends and residual nebula gas is largely removed by T Tauri winds (interval of 3-30 MA).
Why does the gas cloud form a disc?
As the cloud rotates the gravitational force causes the closed to contract. Centrifugal force and gas pressure causes an outward pressure along the plane of rotation. There is no force pushing pole ward so it collapses in.
The conservation of angular momentum inhibits collapse along the equatorial plane.a
What processes caused the sun to loose angular momentum?
Viscous drag led to the outward transfer of angular momentum and the inward transfer of mass.
The T Tauri wind that occurred later would have caused the sur to lose mass and therefore angular momentum.
What 3 processes slow the accretion of dust farther from the protosun?
1 the column mass decreases outwards so grains would be expected to condense more slowly.
2 the lower density means less frequent collisions and a therefore slower **coagulation **.
3 the solar nebula was probably fatter in the after reaches, meaning particles had further to travel to reach the mid-plane taking longer to complete their journeys.
Why are most moons in a prograde orbit with the planet?
It is believed that most moons formed from a proto-planetary disc of gas and dust around the protoplanets.
What is the likely cause of a moon with a retrograde orbit?
Moons with retrograde orbits are likely comets or asteroids that have been captured by the planet.
What is the current favoured theory for the origin of the solar system?
The nebula hypothesis is the current best theory.
A protosun surrounded by a disc of gos and dust rotates and flattens, then separates to form the planets.
In what order did material condense in the solar nebula?
Much of the dust would have initially been vapourized due to extreme heat.
As the nebula cooled refractory substance would have condensed first with more volatile substance condensing later.
No ice would he able to form within 5 au of the protosun however water may have been present as hydrated minerals.
Past 5 au ice was able to condense.
What is coagulation and when did it occur?
When grains of dust condensed, they would move towards the central pane of the disc and gently bump into each other and stick together (coagulated). This occurred as the cloud collapsed to a disc.
Coagulation may have been encouraged by fluffy surface textures, magnetism and electric charges.
What are planetesimals and when did they form?
As the dust coagulated, it formed planetesimals 0.1 - 10 km in size.
This could of happened because of continued coagulation, gravitationally driven turbulence or pebble accretion.
This occurred within a few hundred thousand years of the creation of the solar nebula.
What comes after the formation of planetesimals?
At a size of 10 km, planetesimals gravitational field would be strong enough to encourage collisions. Eventually, the growth of one body would outpace the others forming a planetary embryo.
These probably took an order of 10^4 or 10^5 to form in the inner solar, and then a magnitude of 10 mode for each planet in the outer solar system.
What do planetary embryos form?
Each terrestrial planet forms from the collision of planetary embryos over a period of 10^8 years.
Runaway growth took longer in the outer solar system, but the planetary embryos that grew there became sufficiently large to become kernels around which large masses of gas were captured from the solar nebula.
What was the effect of the sun entering its T Tauri phase?
Solar winds swept remaining gas from the solar nebula out into space before Saturn, Uranus and Neptune could capture as much as Jupiter.
This process also swept away the primitive atmospheres of the terrestrial planets.
What is the grand tack theory?
This states that remaining nebula material in the first 0.1 Ga of the solar system caused Jupiter and Saturn to first migrate inwards, then outwards after.
What is the nice model?
This says that 3.8 - 4 Ga ago Jupiter and Saturn passed through a 2:1 orbital resonance, which destabolised the solar system and accounts for the late heavy bombardment.
Why are the asteroids in the asteroid belt of sub-planetary size?
This can be attributed to the gravitational perturbation of the orbits of planetesimals in this region by Jupiter, therefore any collisions between planetesimals would have been too energetic to lead to runaway growth.
Long period comets and large icy bodies may have been flung out after passing close to Jupiter or another giant planet to form the Oort cloud.
What do the orbits of the moons of Jupiter, Saturn and Uranus suggest?
It suggest these bodies grew out of a protosatellite disc around each planet, rather like a miniature solar nebula.
