TMA 2 Revision

Question 1

Why would a planet with an atmosphere containing Ar, CH4 and N2O have a higher surface temperature than effective temperature?

Answer 1

• CH4 and N2O are both known green house gasses.
• they are polyatomic heteronuclear molecules which excite in their vibrational modes, therefore strongly absorb UV IR radiation.
• The IR radiation passed on by collisions and chemical reactions causing atmospheric heating.

Question 2

How can spectroscopy detect molecules?

Answer 2

• Molecules in the atmosphere absorb IR radiation.
• This excites vibrational modes in wavelengths characteristic of each species.
• These appear as absorption features in the planets continuous spectrum.
• A limit of this method is it can only detect molecules with an electric dipole ( not homonuclear molecules as they have no vibrational spectra).

Question 3

Describe how light curve variations can reveal the shape, spin rate and history of an asteroid?

Answer 3

• Cross sectional observed area changes during rotation giving variation in the amount of light reflected.
• Amplitude of lightcurve indicates degree of elongation.
• Period of light curve reveals spin rate.
• Double peaked curve indicates irregular shape (only alternate peaks matching).
• Regional/hemispheric albedo differences.
• Spherical asteroids were likely to have once been molten.
• Albedo variations suggest complex history.
• Angular asteroids may have suffered many impacts.

Question 4

How was mass lost from the disc of gas and dust surrounding a protosun?

Answer 4

• Mass was lost from the system at the edges of the disc due to viscous drag.
• These action of stellar winds blowing outwards from the poles (bipolar flow).
• Mass was lost from the disc by continued accretion onto the protosun.
• Mass may have been lost during the stars T Tauri phase where strong stellar winds went in all directions.

Question 5

What mass reducing process has a large effect on angular momentum?

Answer 5

The edge outflow of mass and the T Tauri phase could significantly effect the angular momentum on the system.

The bipolar flow would not affect angular momentum much.

Question 6

What events led to planet formation and how does a temperature gradient affect this process?

Answer 6

• The radial temperature gradient went from hot in the centre to cold at the edges of the disc.
• As temp fell in the inner region, solid materials began to condense as dust.
• These eventually coagulated into grains mm in size, which subsequently collected into bodies 0.1-10 km in size known as planetesimals.
• Planetesimals accreted into planetary embryos and eventually planets.
  -In the inner solar system where temperatures remained high, planetesimals would have been primarily composed of rocky materials.
• Further out, planetesimals would have been a mixture of rock and ice, becoming dominated by ice towards the outer edge of the disc.