exoplanets Flashcards
Explain the nature and origin of a chthonian planet
A chthonian planet is a silicate planet orbiting close to its star that formed by the hydrodynamic escape of hydrogen and helium from a Hot Jupiter, leaving only its silicate core
Sketch the variations in brightness of a star associated with the transit or a planet across its face
Explain how this sketch enables you to estimate the diameter of the planet relative to that of the star.
The % magnitude of dimming is the % proportion of the face of the star that is obscured by the planet.
Produce a sketch demonstrating how the transit method can be used to determine the atmospheric chemistry of a planet
- Starlight passes through the atmosphere of an exoplanet during transit
- Use spectrograph to examine spectrum of starlight passing through the atmosphere
- Compare it with spectrum of starlight not passing through the atmosphere
Compare spectrum of light that passed through atmosphere with light directly from star. Additional absorption lines result from atmospheric gases
Differences in absorption lines indicate the atmospheric chemistry.
Stars vary in spectral type from small, faint M-type stars to large, hot O-type stars, as shown below.
Why are small, dim M-type stars a poor target for searches for habitable exoplanets and extraterrestrial life?
They tend to experience giant flares that can irradiate a planet’s surface; a planet within the habitable zone is likely to be tidally locked to the star, presenting the same face to it, with potential for unpleasant climatic effects, such as freezing of the ocean and even atmosphere on the night side.
Stars vary in spectral type from small, faint M-type stars to large, hot O-type stars, as shown below.
Why are large, hot O- and B-type stars poor targets for searches for habitable exoplanets and extraterrestrial life?
Large, hot stars emit a lot of ionising UV and X-ray radiation that reduces the habitability of a planetary surface; they also have short lives and hence less opportunity for life to evolve
Why might the detection of methane and ozone in the atmosphere of an exoplanet be interpreted as evidence of life?
Methane and oxygen are not stable together; one must be experiencing constant replenishment; on Earth, atmospheric methane is replenished by biology
Identify three other processes that could generate atmospheric methane
Interior outgassing (e.g. Titan); meteoritic and cometary infall; serpentinisation of ultramafic crust
Describe three methods by which the existence of a planet may be inferred from its gravitational influence.
The gravity of the planet causes the star to regularly change position as it and the planet orbit their barycentre. Pulsar timing method: if the star is a pulsar, then the planet can be inferred by detecting variations in the timing of the radiation pulses. In the radial velocity method, a planet can be inferred by detecting cycles of variations in the radial velocity of the star, as measured by the Doppler shifts of spectral lines in the star’s spectrum. Or, use astrometry to measure regular changes in the position of star relative to a background reference of distant stars.
