What is direct detection of an exoplanet?
Observing light from the planet separately from the light of its host star.
AQA A-level Physics (7408) · 3.9.3.4
Revise AQA A-level Physics (7408) specification point 3.9.3.4, Detection of exoplanets (A-level only), with free active-recall flashcards. Flip through the set or review every question and answer below.
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What is direct detection of an exoplanet?
Observing light from the planet separately from the light of its host star.
Why can a host star’s brightness overwhelm an exoplanet’s signal?
The planet is much fainter: it emits far less light of its own and reflects only a small fraction of the star’s light.
Why are the images of an exoplanet and its host star difficult to resolve?
Exoplanetary systems are very distant, so the planet and star usually have a very small apparent angular separation.
Why does a star move periodically when a planet orbits it?
The planet’s gravity makes the star move around their common centre of mass.
What causes a star’s spectral lines to shift periodically as a planet orbits it?
The star’s changing motion along the observer’s line of sight produces periodic Doppler shifts.
How do a star’s spectral lines shift when it moves towards versus away from an observer?
Towards: blueshift. Away: redshift.
How can radial velocity measurements reveal an orbiting planet?
Repeated measurements can reveal a periodic change in the star’s radial velocity.
What does the period of a star’s radial velocity variation reveal?
The planet’s orbital period.
What two factors affect the size of a star’s observed radial velocity variation?
The planet’s gravitational effect and the orientation of its orbit.
What is an exoplanet transit?
An orbiting planet passes across the visible disc of its host star from the observer’s viewpoint.
Why does a star’s observed brightness decrease during a planetary transit?
The planet blocks a small fraction of the star’s light.
What does a star’s light curve typically look like during and between planetary transits?
Brightness dips during each transit and remains approximately constant between transits.
What do regularly recurring dips in a star’s brightness provide evidence of?
An orbiting planet.
How can an exoplanet’s orbital period be found from its transit light curve?
Measure the time between successive dips.
What does the fractional depth of a transit dip reveal about the planet?
Its size relative to the star, through the fraction of the stellar disc it blocks.
What orbital alignment is required for a planetary transit to be observable?
The orbit must be suitably aligned with the observer’s line of sight.