Topic 8 Exploring The Solar System Flashcards
What is a protoplanetary disc/solar nebula?
A turbulent rotating disc of dust and gas that is flattened. The initial composition of the solar nebula was that of a dense cloud containing hydrogen, helium and a wide range of molecules as well as silicate and carbon rich dust grains coated with water and other ices.
How do the planetary embryos form?
Dust and gas accrete together to initially form planetesimals. Planetesimals then further collide and accrete material, growing in size until they form planetary embryos.
What dictates the composition of each planet during formation?
The central part the protoplanetary disc was heated to high temperatures by the release of gravitational energy vaporising the original ices and dust. In the region is closest to the centre elements with high melting points will condensate first such as silicates which will then go on to produce the terrestrial planets.
As you get further from the centre, there is a point referred to as the snow line where water ice will be able to condensate beyond this point a small amount of silicate rock material will accumulate and capture the remaining hydrogen and helium from the solar nebula. These will go onto form the gas giants.
How do protoplanets form?
Planetary embryos Clyde to form protoplanets that then sweep up the remaining planet decimals and nebula gas and dust to form the planet scene today.
How did Jupiter help form the astroid belt?
Jupiter is so large that it’s gravity disrupted the orbits of nearby planetesimals, leading to fragmentation through collision rather than accretion. Current astroid belt is the remnant of the original planetesimals and planetary embryos that were prevented from creating to form a planet.
A few larger planetesimals remained such as Ceres and Vesta.
How did the Kuiper belt form?
Icy planetesimals that approached Jupiter but were not accreted were scattered into new orbits. One population of icy planetesimals remaining in the ecliptic plane formed the Kuiper belt.
How did the Oort Cloud form?
Some icy planetesimals that were near Jupiter but not accreted were ejected on highly eccentric orbits to form the Oort cloud.
What is the Nice model?
The model proposes that after their formation the gas giants had orbits much closer together than they do now. The Kuiper belt was more dense and closer to the Sun. The orbits of the planets evolved because of their mutual gravitational influences and those of the remaining planetesimals. The net effects were that Jupiter moved slightly inward while the other planets moved outwards. Neptune originally closer to the sun Uranus moved outside the orbit of Uranus and disrupted the original Kuiper Belt.
What are the three classes of Kuiper belt objects (KBO)?
Plutinos - these are objects with an orbital resonance with Neptune. They typically have a semi major axis of approximately 40 AU. Pluto has an orbital resonance with Neptune of 3:2.
Classical objects - these are objects that have a semimajor axis of approximately 45 AU and a low eccentricity.
Scattered disc objects - these objects typically have a semimajor axis above 45 AU and high eccentricity’s.
Why does the spectrum of KBO appear reddened?
This is because the surface of the KBO’s has been modified by impacts and radiation.
What ices have been found on Pluto’s surface?
Carbon, methane and water ice have all been identified on Pluto surface.
What is the estimated mass of the astroid belt and the Kuiper belt?
The estimated mass of the asteroids belt is 0.001 earth masses.
The estimated mass of the Kuiper about is 0.1 earth masses.
What are comets?
Comets are small bodies of dust and ice, typically a few kilometres across. Their icy compositions indicate that they are formed in the outer parts of the solar system, outside the snow line.
They are relatively unaltered since their formation in the solar nebula.
What pathway do comets take through the solar system?
Comments can have extremely elongated elliptical orbits, inclined to any angle to the plane of the solar system.
Why do comets have two tails?
As the comet approaches the Sun, it becomes more active. Ice sublimes, releasing gas and dust, which form a coma around the nucleus. Comets grow two tails, one of dust, the other of ionised particles.
What are the main constituents of a comet nucleus?
A comet nucleus is typically made up of dust ice and gas. They are thought to be a relatively low density approximately 500 kg per meter cubed which is half as dense as water ice.
This means that the comet nucleus is very porous.
Why does a comet nucleus have active and less active regions?
As ice at the surface sublimes a dusty layer is left behind building a dark un reflective layer. This layer shields the icy layers beneath from sunlight, and so a cometary nucleus does not release gas from its entire surface at all times. Active regions on the surface are where the ice is exposed.
Cracks and fissures in the surface may also give rise to jets of gas and dust.
What are the two main types of comet classification?
Long period comets - these are comets that had come from the Oort cloud, so have semi major axis of hundreds or even thousands of AU. These comets can enter the inner solar system from any direction, and so their orbital inclination can take any value. These comets have very long orbital periods.
Short period comets - these comments have a semi major axis less than that of Neptune. These are thought to come from the Kuiper belt. Some body’s in the Kuiper belt our thought to migrate inwards under Jupiter’s gravitational influence.
