Why is direct detection of exoplanets difficult in terms of relative brightness?

Exoplanets are extremely faint compared to their host stars, which are typically billions of times brighter.

What geometric factor makes direct imaging of exoplanets challenging from Earth?

The angular separation between an exoplanet and its host star is very small when viewed from Earth.

How does the host star's light affect attempts to directly observe an exoplanet?

Light from the host star overwhelms any light reflected or emitted by the planet, making the planet undetectable.

What observable quantity does the radial velocity method measure to detect exoplanets?

It measures periodic variations in the Doppler shift of light from the host star.

Why does a star wobble when it has an orbiting exoplanet?

The star and planet orbit their common centre of mass, causing the star to move towards and away from Earth.

In the radial velocity method, what happens to the star's spectral lines when the star moves towards Earth?

The spectral lines are blueshifted.

AQA A-Level Physics 7408

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Astrophysics

Detection of exoplanets

4 things to know
Paper 3, section B

Overview

The radial velocity and transit methods, and reading a light curve.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

Why is directly imaging an exoplanet hard, and what does the radial velocity method measure?

Process

How does the transit method detect a planet, what sets the depth of the brightness dip, and what orbital alignment does it require?

Numbers

What does a transit light curve look like, and how is the orbital period found from it?

Process

What happens to the observed brightness as the planet exits the stellar disc?

Questions from this subtopic

Each one with the model answer underneath.

1
Why is direct detection of exoplanets difficult in terms of relative brightness?
Model answer
Exoplanets are extremely faint compared to their host stars, which are typically billions of times brighter.
2
What geometric factor makes direct imaging of exoplanets challenging from Earth?
Model answer
The angular separation between an exoplanet and its host star is very small when viewed from Earth.
3
How does the host star's light affect attempts to directly observe an exoplanet?
Model answer
Light from the host star overwhelms any light reflected or emitted by the planet, making the planet undetectable.
4
What observable quantity does the radial velocity method measure to detect exoplanets?
Model answer
It measures periodic variations in the Doppler shift of light from the host star.
5
Why does a star wobble when it has an orbiting exoplanet?
Model answer
The star and planet orbit their common centre of mass, causing the star to move towards and away from Earth.
6
In the radial velocity method, what happens to the star's spectral lines when the star moves towards Earth?
Model answer
The spectral lines are blueshifted.

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