1
Q
What is nucleosynthesis, and when does it occur?
A
- The process of creating elements
- Big Bang: all H in universe, most He, some Li
- Stellar nucleosynthesis (fusion): all elements up to Fe (most stable)
- Stellar death (supernovae): high energy, all naturally occuring elements after Fe
2
Q
How can the bulk composition of the Earth be estimated?
A
- Carbonaceous chondrites (same composition as the nebula which formed Earth), the Sun (99.86% mass of solar system)
3
Q
Describe the process of planetary formation
A
- Protoplanetary disc formed by material accreted by young star. Disc due to angular momentum conservation
- Disc has large radial temp gradient since star heats centre
- Ca/Al rich inclusions condense out of gas (solid), followed by chondrules (silicate melt)
- Substances condense in order of increasing volatility
- Accretion: globules come together by gravity to form a planet. Process is uncertain.
4
Q
Describe the process of planetary differentiation
A
- Rocky bodies become large enough that the internal temperature reaches melting point of some materials
- Allows denser materials to sink to centre and lighter ones to rise (lower GPE)
- Hence Fe cores formed, silicates rise. Within silicates, basalts form crust and peridotite forms mantle
- On Earth, process released H2O, CO2, N2 into atmosphere
5
Q
How are exoplanets detected?
A
- Transit method: detects temporary dimming as planet passes in front of star
- Dimming can also occur when it moves behind since we see the illuminated face of the planet beforehand
- Radial velocity can be found from Doppler shift in star wavelength since they orbit mutual CoM
- Direct imaging possible but difficult since star’s light is overwhelming
6
Q
Which exoplanet types raise questions about the planetary formation model?
A
- Hot Jupiters: gas giants in close orbit around stars
- Model suggests volatile-rich planets should form far from stars in cooler region
- Super Earths: terran planets much larger than Earth
- Raises questions of how large rocky planets can be while having similar tectonics/climate to Earth
7
Q
What is the general distribution of exoplanets?
A
- Most exoplanets are terrestrial
- Most are around smaller stars
- Large stars too hot, leading to atmospheric escape
8
Q
How can exoplanets be categorised?
A
- Radius can be calculated from dimming of star and orbital period, hence density can be estimated
- Atmospheric absorption spectra of starlight can be used to estimate composition
- Planets categorised into rocky planets/gas giants
- Planets of intermediate radius/mass hard to categorise, eg water decreasing avg density
9
Q
What conditions are necessary for habitability?
A
- Elements C, H, N, O, P, S
- C,H,N volatile so concentrate in atmosphere, P and S form alloys so concentrate in metallic core
